| Message ID | 20090707210849.21953.93817.stgit@dev.haskins.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Gregory Haskins wrote: > ioeventfd is a mechanism to register PIO/MMIO regions to trigger an eventfd > signal when written to by a guest. Host userspace can register any > arbitrary IO address with a corresponding eventfd and then pass the eventfd > to a specific end-point of interest for handling. > > Normal IO requires a blocking round-trip since the operation may cause > side-effects in the emulated model or may return data to the caller. > Therefore, an IO in KVM traps from the guest to the host, causes a VMX/SVM > "heavy-weight" exit back to userspace, and is ultimately serviced by qemu's > device model synchronously before returning control back to the vcpu. > > However, there is a subclass of IO which acts purely as a trigger for > other IO (such as to kick off an out-of-band DMA request, etc). For these > patterns, the synchronous call is particularly expensive since we really > only want to simply get our notification transmitted asychronously and > return as quickly as possible. All the sychronous infrastructure to ensure > proper data-dependencies are met in the normal IO case are just unecessary > overhead for signalling. This adds additional computational load on the > system, as well as latency to the signalling path. > > Therefore, we provide a mechanism for registration of an in-kernel trigger > point that allows the VCPU to only require a very brief, lightweight > exit just long enough to signal an eventfd. This also means that any > clients compatible with the eventfd interface (which includes userspace > and kernelspace equally well) can now register to be notified. The end > result should be a more flexible and higher performance notification API > for the backend KVM hypervisor and perhipheral components. > > To test this theory, we built a test-harness called "doorbell". This > module has a function called "doorbell_ring()" which simply increments a > counter for each time the doorbell is signaled. It supports signalling > from either an eventfd, or an ioctl(). > > We then wired up two paths to the doorbell: One via QEMU via a registered > io region and through the doorbell ioctl(). The other is direct via > ioeventfd. > > You can download this test harness here: > > ftp://ftp.novell.com/dev/ghaskins/doorbell.tar.bz2 > > The measured results are as follows: > > qemu-mmio: 110000 iops, 9.09us rtt > ioeventfd-mmio: 200100 iops, 5.00us rtt > ioeventfd-pio: 367300 iops, 2.72us rtt > > I didn't measure qemu-pio, because I have to figure out how to register a > PIO region with qemu's device model, and I got lazy. However, for now we > can extrapolate based on the data from the NULLIO runs of +2.56us for MMIO, > and -350ns for HC, we get: > > qemu-pio: 153139 iops, 6.53us rtt > ioeventfd-hc: 412585 iops, 2.37us rtt > > these are just for fun, for now, until I can gather more data. > > Here is a graph for your convenience: > > http://developer.novell.com/wiki/images/7/76/Iofd-chart.png > > The conclusion to draw is that we save about 4us by skipping the userspace > hop. > > -------------------- > > Signed-off-by: Gregory Haskins <ghaskins@novell.com> > --- > > arch/x86/kvm/x86.c | 1 > include/linux/kvm.h | 24 ++++ > include/linux/kvm_host.h | 10 +- > virt/kvm/eventfd.c | 252 ++++++++++++++++++++++++++++++++++++++++++++++ > virt/kvm/kvm_main.c | 11 ++ > 5 files changed, 294 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 95fa45c..59c2d93 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1212,6 +1212,7 @@ int kvm_dev_ioctl_check_extension(long ext) > case KVM_CAP_IRQ_INJECT_STATUS: > case KVM_CAP_ASSIGN_DEV_IRQ: > case KVM_CAP_IRQFD: > + case KVM_CAP_IOEVENTFD: > case KVM_CAP_PIT2: > r = 1; > break; > diff --git a/include/linux/kvm.h b/include/linux/kvm.h > index 76c6408..22d0eb7 100644 > --- a/include/linux/kvm.h > +++ b/include/linux/kvm.h > @@ -307,6 +307,28 @@ struct kvm_guest_debug { > struct kvm_guest_debug_arch arch; > }; > > +enum { > + kvm_ioeventfd_flag_nr_datamatch, > + kvm_ioeventfd_flag_nr_pio, > + kvm_ioeventfd_flag_nr_deassign, > + kvm_ioeventfd_flag_nr_max, > +}; > + > +#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch) > +#define KVM_IOEVENTFD_FLAG_PIO (1 << kvm_ioeventfd_flag_nr_pio) > +#define KVM_IOEVENTFD_FLAG_DEASSIGN (1 << kvm_ioeventfd_flag_nr_deassign) > + > +#define KVM_IOEVENTFD_VALID_FLAG_MASK ((1 << kvm_ioeventfd_flag_nr_max) - 1) > + > +struct kvm_ioeventfd { > + __u64 datamatch; > + __u64 addr; /* legal pio/mmio address */ > + __u32 len; /* 1, 2, 4, or 8 bytes */ > + __s32 fd; > + __u32 flags; > + __u8 pad[36]; > +}; > + > #define KVM_TRC_SHIFT 16 > /* > * kvm trace categories > @@ -409,6 +431,7 @@ struct kvm_guest_debug { > #define KVM_CAP_PIT2 33 > #endif > #define KVM_CAP_SET_BOOT_CPU_ID 34 > +#define KVM_CAP_IOEVENTFD 35 > > #ifdef KVM_CAP_IRQ_ROUTING > > @@ -517,6 +540,7 @@ struct kvm_irqfd { > #define KVM_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd) > #define KVM_CREATE_PIT2 _IOW(KVMIO, 0x77, struct kvm_pit_config) > #define KVM_SET_BOOT_CPU_ID _IO(KVMIO, 0x78) > +#define KVM_IOEVENTFD _IOW(KVMIO, 0x79, struct kvm_ioeventfd) > > /* > * ioctls for vcpu fds > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 306bc67..0347d59 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -154,6 +154,7 @@ struct kvm { > spinlock_t lock; > struct list_head items; > } irqfds; > + struct list_head ioeventfds; > #endif > struct kvm_vm_stat stat; > struct kvm_arch arch; > @@ -532,19 +533,24 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {} > > #ifdef CONFIG_HAVE_KVM_EVENTFD > > -void kvm_irqfd_init(struct kvm *kvm); > +void kvm_eventfd_init(struct kvm *kvm); > int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags); > void kvm_irqfd_release(struct kvm *kvm); > +int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args); > > #else > > -static inline void kvm_irqfd_init(struct kvm *kvm) {} > +static inline void kvm_eventfd_init(struct kvm *kvm) {} > static inline int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) > { > return -EINVAL; > } > > static inline void kvm_irqfd_release(struct kvm *kvm) {} > +static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + return -ENOSYS; > +} > > #endif /* CONFIG_HAVE_KVM_EVENTFD */ > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 4092b8d..eee8edb 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -21,6 +21,7 @@ > */ > > #include <linux/kvm_host.h> > +#include <linux/kvm.h> > #include <linux/workqueue.h> > #include <linux/syscalls.h> > #include <linux/wait.h> > @@ -28,6 +29,9 @@ > #include <linux/file.h> > #include <linux/list.h> > #include <linux/eventfd.h> > +#include <linux/kernel.h> > + > +#include "iodev.h" > > /* > * -------------------------------------------------------------------- > @@ -234,10 +238,11 @@ fail: > } > > void > -kvm_irqfd_init(struct kvm *kvm) > +kvm_eventfd_init(struct kvm *kvm) > { > spin_lock_init(&kvm->irqfds.lock); > INIT_LIST_HEAD(&kvm->irqfds.items); > + INIT_LIST_HEAD(&kvm->ioeventfds); > } > > /* > @@ -327,3 +332,248 @@ static void __exit irqfd_module_exit(void) > > module_init(irqfd_module_init); > module_exit(irqfd_module_exit); > + > +/* > + * -------------------------------------------------------------------- > + * ioeventfd: translate a PIO/MMIO memory write to an eventfd signal. > + * > + * userspace can register a PIO/MMIO address with an eventfd for receiving > + * notification when the memory has been touched. > + * -------------------------------------------------------------------- > + */ > + > +struct _ioeventfd { > + struct list_head list; > + u64 addr; > + int length; > + struct eventfd_ctx *eventfd; > + u64 datamatch; > + struct kvm_io_device dev; > + bool wildcard; > +}; > + > +static inline struct _ioeventfd * > +to_ioeventfd(struct kvm_io_device *dev) > +{ > + return container_of(dev, struct _ioeventfd, dev); > +} > + > +static void > +ioeventfd_release(struct _ioeventfd *p) > +{ > + eventfd_ctx_put(p->eventfd); > + list_del(&p->list); > + kfree(p); > +} > + > +static bool > +ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val) > +{ > + u64 _val; > + > + if (!(addr == p->addr && len == p->length)) > + /* address-range must be precise for a hit */ > + return false; > + > + if (p->wildcard) > + /* all else equal, wildcard is always a hit */ > + return true; > + > + /* otherwise, we have to actually compare the data */ > + > + BUG_ON(!IS_ALIGNED((unsigned long)val, len)); > + > + switch (len) { > + case 1: > + _val = *(u8 *)val; > + break; > + case 2: > + _val = *(u16 *)val; > + break; > + case 4: > + _val = *(u32 *)val; > + break; > + case 8: > + _val = *(u64 *)val; > + break; > + default: > + return false; > + } > + > + return _val == p->datamatch ? true : false; > +} > + > +/* MMIO/PIO writes trigger an event if the addr/val match */ > +static int > +ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len, > + const void *val) > +{ > + struct _ioeventfd *p = to_ioeventfd(this); > + > + if (!ioeventfd_in_range(p, addr, len, val)) > + return -EOPNOTSUPP; > + > + eventfd_signal(p->eventfd, 1); > + return 0; > +} > + > +/* > + * This function is called as KVM is completely shutting down. We do not > + * need to worry about locking just nuke anything we have as quickly as possible > + */ > +static void > +ioeventfd_destructor(struct kvm_io_device *this) > +{ > + struct _ioeventfd *p = to_ioeventfd(this); > + > + ioeventfd_release(p); > +} > + > +static const struct kvm_io_device_ops ioeventfd_ops = { > + .write = ioeventfd_write, > + .destructor = ioeventfd_destructor, > +}; > + > +/* assumes kvm->slots_lock held */ > +static bool > +ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p) > +{ > + struct _ioeventfd *_p; > + > + list_for_each_entry(_p, &kvm->ioeventfds, list) > + if (_p->addr == p->addr && _p->length == p->length && > + (_p->wildcard || p->wildcard || > + _p->datamatch == p->datamatch)) > + return true; > + > + return false; > +} > + > +static int > +kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; > + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; > + struct _ioeventfd *p; > + struct eventfd_ctx *eventfd; > + int ret; > + > + /* must be natural-word sized */ > + switch (args->len) { > + case 1: > + case 2: > + case 4: > + case 8: > + break; > + default: > + return -EINVAL; > + } > + > + /* check for range overflow */ > + if (args->addr + args->len < args->addr) > + return -EINVAL; > + > + /* check for extra flags that we don't understand */ > + if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK) > + return -EINVAL; > + > + eventfd = eventfd_ctx_fdget(args->fd); > + if (IS_ERR(eventfd)) > + return PTR_ERR(eventfd); > + > + p = kzalloc(sizeof(*p), GFP_KERNEL); > + if (!p) { > + ret = -ENOMEM; > + goto fail; > + } > + > + INIT_LIST_HEAD(&p->list); > + p->addr = args->addr; > + p->length = args->len; > + p->eventfd = eventfd; > + > + /* The datamatch feature is optional, otherwise this is a wildcard */ > + if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH) > + p->datamatch = args->datamatch; > + else > + p->wildcard = true; > + > + down_write(&kvm->slots_lock); > + > + /* Verify that there isnt a match already */ > + if (ioeventfd_check_collision(kvm, p)) { > + ret = -EEXIST; > + goto unlock_fail; > + } > + > + kvm_iodevice_init(&p->dev, &ioeventfd_ops); > + > + ret = __kvm_io_bus_register_dev(bus, &p->dev); > + if (ret < 0) > + goto unlock_fail; > + > + list_add_tail(&p->list, &kvm->ioeventfds); > + > + up_write(&kvm->slots_lock); > + > + return 0; > + > +unlock_fail: > + up_write(&kvm->slots_lock); > + > +fail: > + kfree(p); > + eventfd_ctx_put(eventfd); > + > + return ret; > +} > + > +static int > +kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; > + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; > + struct _ioeventfd *p, *tmp; > + struct eventfd_ctx *eventfd; > + int ret = -ENOENT; > + > + eventfd = eventfd_ctx_fdget(args->fd); > + if (IS_ERR(eventfd)) > + return PTR_ERR(eventfd); > + > + down_write(&kvm->slots_lock); > + > + list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) { > + bool wildcard = args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH ? > + true : false; > Doh! Inverted logic. "wildcard" should be "false" if DATAMATCH is defined in the flags. Avi, please reverse true/false here before accepting (assuming a v11 respin isn't needed). Of course, if you would prefer me to just submit a new patch, that is fine too. -Greg > + > + if (p->eventfd != eventfd || > + p->addr != args->addr || > + p->length != args->len || > + p->wildcard != wildcard) > + continue; > + > + if (!p->wildcard && p->datamatch != args->datamatch) > + continue; > + > + __kvm_io_bus_unregister_dev(bus, &p->dev); > + ioeventfd_release(p); > + ret = 0; > + break; > + } > + > + up_write(&kvm->slots_lock); > + > + eventfd_ctx_put(eventfd); > + > + return ret; > +} > + > +int > +kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN) > + return kvm_deassign_ioeventfd(kvm, args); > + > + return kvm_assign_ioeventfd(kvm, args); > +} > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index dd92b44..14e1f32 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -979,7 +979,7 @@ static struct kvm *kvm_create_vm(void) > spin_lock_init(&kvm->mmu_lock); > spin_lock_init(&kvm->requests_lock); > kvm_io_bus_init(&kvm->pio_bus); > - kvm_irqfd_init(kvm); > + kvm_eventfd_init(kvm); > mutex_init(&kvm->lock); > mutex_init(&kvm->irq_lock); > kvm_io_bus_init(&kvm->mmio_bus); > @@ -2271,6 +2271,15 @@ static long kvm_vm_ioctl(struct file *filp, > r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags); > break; > } > + case KVM_IOEVENTFD: { > + struct kvm_ioeventfd data; > + > + r = -EFAULT; > + if (copy_from_user(&data, argp, sizeof data)) > + goto out; > + r = kvm_ioeventfd(kvm, &data); > + break; > + } > #ifdef CONFIG_KVM_APIC_ARCHITECTURE > case KVM_SET_BOOT_CPU_ID: > r = 0; > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
Not worth respinning for, but if you do generate v11 On Tue, Jul 07, 2009 at 05:08:49PM -0400, Gregory Haskins wrote: > ioeventfd is a mechanism to register PIO/MMIO regions to trigger an eventfd > signal when written to by a guest. Host userspace can register any > arbitrary IO address with a corresponding eventfd and then pass the eventfd > to a specific end-point of interest for handling. > > Normal IO requires a blocking round-trip since the operation may cause > side-effects in the emulated model or may return data to the caller. > Therefore, an IO in KVM traps from the guest to the host, causes a VMX/SVM > "heavy-weight" exit back to userspace, and is ultimately serviced by qemu's > device model synchronously before returning control back to the vcpu. > > However, there is a subclass of IO which acts purely as a trigger for > other IO (such as to kick off an out-of-band DMA request, etc). For these > patterns, the synchronous call is particularly expensive since we really > only want to simply get our notification transmitted asychronously and > return as quickly as possible. All the sychronous infrastructure to ensure > proper data-dependencies are met in the normal IO case are just unecessary > overhead for signalling. This adds additional computational load on the > system, as well as latency to the signalling path. > > Therefore, we provide a mechanism for registration of an in-kernel trigger > point that allows the VCPU to only require a very brief, lightweight > exit just long enough to signal an eventfd. This also means that any > clients compatible with the eventfd interface (which includes userspace > and kernelspace equally well) can now register to be notified. The end > result should be a more flexible and higher performance notification API > for the backend KVM hypervisor and perhipheral components. > > To test this theory, we built a test-harness called "doorbell". This > module has a function called "doorbell_ring()" which simply increments a > counter for each time the doorbell is signaled. It supports signalling > from either an eventfd, or an ioctl(). > > We then wired up two paths to the doorbell: One via QEMU via a registered > io region and through the doorbell ioctl(). The other is direct via > ioeventfd. > > You can download this test harness here: > > ftp://ftp.novell.com/dev/ghaskins/doorbell.tar.bz2 > > The measured results are as follows: > > qemu-mmio: 110000 iops, 9.09us rtt > ioeventfd-mmio: 200100 iops, 5.00us rtt > ioeventfd-pio: 367300 iops, 2.72us rtt > > I didn't measure qemu-pio, because I have to figure out how to register a > PIO region with qemu's device model, and I got lazy. However, for now we > can extrapolate based on the data from the NULLIO runs of +2.56us for MMIO, > and -350ns for HC, we get: > > qemu-pio: 153139 iops, 6.53us rtt > ioeventfd-hc: 412585 iops, 2.37us rtt > > these are just for fun, for now, until I can gather more data. > > Here is a graph for your convenience: > > http://developer.novell.com/wiki/images/7/76/Iofd-chart.png > > The conclusion to draw is that we save about 4us by skipping the userspace > hop. > > -------------------- > > Signed-off-by: Gregory Haskins <ghaskins@novell.com> > --- > > arch/x86/kvm/x86.c | 1 > include/linux/kvm.h | 24 ++++ > include/linux/kvm_host.h | 10 +- > virt/kvm/eventfd.c | 252 ++++++++++++++++++++++++++++++++++++++++++++++ > virt/kvm/kvm_main.c | 11 ++ > 5 files changed, 294 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 95fa45c..59c2d93 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1212,6 +1212,7 @@ int kvm_dev_ioctl_check_extension(long ext) > case KVM_CAP_IRQ_INJECT_STATUS: > case KVM_CAP_ASSIGN_DEV_IRQ: > case KVM_CAP_IRQFD: > + case KVM_CAP_IOEVENTFD: > case KVM_CAP_PIT2: > r = 1; > break; > diff --git a/include/linux/kvm.h b/include/linux/kvm.h > index 76c6408..22d0eb7 100644 > --- a/include/linux/kvm.h > +++ b/include/linux/kvm.h > @@ -307,6 +307,28 @@ struct kvm_guest_debug { > struct kvm_guest_debug_arch arch; > }; > > +enum { > + kvm_ioeventfd_flag_nr_datamatch, > + kvm_ioeventfd_flag_nr_pio, > + kvm_ioeventfd_flag_nr_deassign, > + kvm_ioeventfd_flag_nr_max, > +}; > + > +#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch) > +#define KVM_IOEVENTFD_FLAG_PIO (1 << kvm_ioeventfd_flag_nr_pio) > +#define KVM_IOEVENTFD_FLAG_DEASSIGN (1 << kvm_ioeventfd_flag_nr_deassign) > + > +#define KVM_IOEVENTFD_VALID_FLAG_MASK ((1 << kvm_ioeventfd_flag_nr_max) - 1) > + > +struct kvm_ioeventfd { > + __u64 datamatch; > + __u64 addr; /* legal pio/mmio address */ > + __u32 len; /* 1, 2, 4, or 8 bytes */ > + __s32 fd; > + __u32 flags; > + __u8 pad[36]; > +}; > + > #define KVM_TRC_SHIFT 16 > /* > * kvm trace categories > @@ -409,6 +431,7 @@ struct kvm_guest_debug { > #define KVM_CAP_PIT2 33 > #endif > #define KVM_CAP_SET_BOOT_CPU_ID 34 > +#define KVM_CAP_IOEVENTFD 35 > > #ifdef KVM_CAP_IRQ_ROUTING > > @@ -517,6 +540,7 @@ struct kvm_irqfd { > #define KVM_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd) > #define KVM_CREATE_PIT2 _IOW(KVMIO, 0x77, struct kvm_pit_config) > #define KVM_SET_BOOT_CPU_ID _IO(KVMIO, 0x78) > +#define KVM_IOEVENTFD _IOW(KVMIO, 0x79, struct kvm_ioeventfd) > > /* > * ioctls for vcpu fds > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index 306bc67..0347d59 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -154,6 +154,7 @@ struct kvm { > spinlock_t lock; > struct list_head items; > } irqfds; > + struct list_head ioeventfds; > #endif > struct kvm_vm_stat stat; > struct kvm_arch arch; > @@ -532,19 +533,24 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {} > > #ifdef CONFIG_HAVE_KVM_EVENTFD > > -void kvm_irqfd_init(struct kvm *kvm); > +void kvm_eventfd_init(struct kvm *kvm); > int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags); > void kvm_irqfd_release(struct kvm *kvm); > +int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args); > > #else > > -static inline void kvm_irqfd_init(struct kvm *kvm) {} > +static inline void kvm_eventfd_init(struct kvm *kvm) {} > static inline int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) > { > return -EINVAL; > } > > static inline void kvm_irqfd_release(struct kvm *kvm) {} > +static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + return -ENOSYS; > +} > > #endif /* CONFIG_HAVE_KVM_EVENTFD */ > > diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c > index 4092b8d..eee8edb 100644 > --- a/virt/kvm/eventfd.c > +++ b/virt/kvm/eventfd.c > @@ -21,6 +21,7 @@ > */ > > #include <linux/kvm_host.h> > +#include <linux/kvm.h> > #include <linux/workqueue.h> > #include <linux/syscalls.h> > #include <linux/wait.h> > @@ -28,6 +29,9 @@ > #include <linux/file.h> > #include <linux/list.h> > #include <linux/eventfd.h> > +#include <linux/kernel.h> > + > +#include "iodev.h" > > /* > * -------------------------------------------------------------------- > @@ -234,10 +238,11 @@ fail: > } > > void > -kvm_irqfd_init(struct kvm *kvm) > +kvm_eventfd_init(struct kvm *kvm) > { > spin_lock_init(&kvm->irqfds.lock); > INIT_LIST_HEAD(&kvm->irqfds.items); > + INIT_LIST_HEAD(&kvm->ioeventfds); > } > > /* > @@ -327,3 +332,248 @@ static void __exit irqfd_module_exit(void) > > module_init(irqfd_module_init); > module_exit(irqfd_module_exit); > + > +/* > + * -------------------------------------------------------------------- > + * ioeventfd: translate a PIO/MMIO memory write to an eventfd signal. > + * > + * userspace can register a PIO/MMIO address with an eventfd for receiving > + * notification when the memory has been touched. > + * -------------------------------------------------------------------- > + */ > + > +struct _ioeventfd { > + struct list_head list; > + u64 addr; > + int length; > + struct eventfd_ctx *eventfd; > + u64 datamatch; > + struct kvm_io_device dev; > + bool wildcard; > +}; > + > +static inline struct _ioeventfd * > +to_ioeventfd(struct kvm_io_device *dev) > +{ > + return container_of(dev, struct _ioeventfd, dev); > +} > + > +static void > +ioeventfd_release(struct _ioeventfd *p) > +{ > + eventfd_ctx_put(p->eventfd); > + list_del(&p->list); > + kfree(p); > +} > + > +static bool > +ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val) > +{ > + u64 _val; > + > + if (!(addr == p->addr && len == p->length)) > + /* address-range must be precise for a hit */ > + return false; > + > + if (p->wildcard) > + /* all else equal, wildcard is always a hit */ > + return true; > + > + /* otherwise, we have to actually compare the data */ > + > + BUG_ON(!IS_ALIGNED((unsigned long)val, len)); > + > + switch (len) { > + case 1: > + _val = *(u8 *)val; > + break; > + case 2: > + _val = *(u16 *)val; > + break; > + case 4: > + _val = *(u32 *)val; > + break; > + case 8: > + _val = *(u64 *)val; > + break; > + default: > + return false; > + } > + > + return _val == p->datamatch ? true : false; Just return _val == p->datamatch is clearer. > +} > + > +/* MMIO/PIO writes trigger an event if the addr/val match */ > +static int > +ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len, > + const void *val) > +{ > + struct _ioeventfd *p = to_ioeventfd(this); > + > + if (!ioeventfd_in_range(p, addr, len, val)) > + return -EOPNOTSUPP; > + > + eventfd_signal(p->eventfd, 1); > + return 0; > +} > + > +/* > + * This function is called as KVM is completely shutting down. We do not > + * need to worry about locking just nuke anything we have as quickly as possible > + */ > +static void > +ioeventfd_destructor(struct kvm_io_device *this) > +{ > + struct _ioeventfd *p = to_ioeventfd(this); > + > + ioeventfd_release(p); > +} > + > +static const struct kvm_io_device_ops ioeventfd_ops = { > + .write = ioeventfd_write, > + .destructor = ioeventfd_destructor, > +}; > + > +/* assumes kvm->slots_lock held */ > +static bool > +ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p) > +{ > + struct _ioeventfd *_p; > + > + list_for_each_entry(_p, &kvm->ioeventfds, list) > + if (_p->addr == p->addr && _p->length == p->length && > + (_p->wildcard || p->wildcard || > + _p->datamatch == p->datamatch)) > + return true; > + > + return false; > +} > + > +static int > +kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; > + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; > + struct _ioeventfd *p; > + struct eventfd_ctx *eventfd; > + int ret; > + > + /* must be natural-word sized */ > + switch (args->len) { > + case 1: > + case 2: > + case 4: > + case 8: > + break; > + default: > + return -EINVAL; > + } > + > + /* check for range overflow */ > + if (args->addr + args->len < args->addr) > + return -EINVAL; > + > + /* check for extra flags that we don't understand */ > + if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK) > + return -EINVAL; > + > + eventfd = eventfd_ctx_fdget(args->fd); > + if (IS_ERR(eventfd)) > + return PTR_ERR(eventfd); > + > + p = kzalloc(sizeof(*p), GFP_KERNEL); > + if (!p) { > + ret = -ENOMEM; > + goto fail; > + } > + > + INIT_LIST_HEAD(&p->list); > + p->addr = args->addr; > + p->length = args->len; > + p->eventfd = eventfd; > + > + /* The datamatch feature is optional, otherwise this is a wildcard */ > + if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH) > + p->datamatch = args->datamatch; > + else > + p->wildcard = true; > + > + down_write(&kvm->slots_lock); > + > + /* Verify that there isnt a match already */ > + if (ioeventfd_check_collision(kvm, p)) { > + ret = -EEXIST; > + goto unlock_fail; > + } > + > + kvm_iodevice_init(&p->dev, &ioeventfd_ops); > + > + ret = __kvm_io_bus_register_dev(bus, &p->dev); > + if (ret < 0) > + goto unlock_fail; > + > + list_add_tail(&p->list, &kvm->ioeventfds); > + > + up_write(&kvm->slots_lock); > + > + return 0; > + > +unlock_fail: > + up_write(&kvm->slots_lock); > + > +fail: > + kfree(p); > + eventfd_ctx_put(eventfd); > + > + return ret; > +} > + > +static int > +kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; > + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; > + struct _ioeventfd *p, *tmp; > + struct eventfd_ctx *eventfd; > + int ret = -ENOENT; > + > + eventfd = eventfd_ctx_fdget(args->fd); > + if (IS_ERR(eventfd)) > + return PTR_ERR(eventfd); > + > + down_write(&kvm->slots_lock); > + > + list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) { > + bool wildcard = args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH ? > + true : false; Just !(args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH) is clearer. > + > + if (p->eventfd != eventfd || > + p->addr != args->addr || > + p->length != args->len || > + p->wildcard != wildcard) > + continue; > + > + if (!p->wildcard && p->datamatch != args->datamatch) > + continue; > + > + __kvm_io_bus_unregister_dev(bus, &p->dev); > + ioeventfd_release(p); > + ret = 0; > + break; > + } > + > + up_write(&kvm->slots_lock); > + > + eventfd_ctx_put(eventfd); > + > + return ret; > +} > + > +int > +kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) > +{ > + if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN) > + return kvm_deassign_ioeventfd(kvm, args); > + > + return kvm_assign_ioeventfd(kvm, args); > +} > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index dd92b44..14e1f32 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -979,7 +979,7 @@ static struct kvm *kvm_create_vm(void) > spin_lock_init(&kvm->mmu_lock); > spin_lock_init(&kvm->requests_lock); > kvm_io_bus_init(&kvm->pio_bus); > - kvm_irqfd_init(kvm); > + kvm_eventfd_init(kvm); > mutex_init(&kvm->lock); > mutex_init(&kvm->irq_lock); > kvm_io_bus_init(&kvm->mmio_bus); > @@ -2271,6 +2271,15 @@ static long kvm_vm_ioctl(struct file *filp, > r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags); > break; > } > + case KVM_IOEVENTFD: { > + struct kvm_ioeventfd data; > + > + r = -EFAULT; > + if (copy_from_user(&data, argp, sizeof data)) > + goto out; > + r = kvm_ioeventfd(kvm, &data); > + break; > + } > #ifdef CONFIG_KVM_APIC_ARCHITECTURE > case KVM_SET_BOOT_CPU_ID: > r = 0; -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/09/2009 06:00 PM, Gregory Haskins wrote: > >> + bool wildcard = args->flags& KVM_IOEVENTFD_FLAG_DATAMATCH ? >> + true : false; >> >> > Doh! Inverted logic. "wildcard" should be "false" if DATAMATCH is > defined in the flags. > > Avi, please reverse true/false here before accepting (assuming a v11 > respin isn't needed). Of course, if you would prefer me to just submit > a new patch, that is fine too. > > I changed it to !(...). I find the predicate ? true : false idiom confusing.
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 95fa45c..59c2d93 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1212,6 +1212,7 @@ int kvm_dev_ioctl_check_extension(long ext) case KVM_CAP_IRQ_INJECT_STATUS: case KVM_CAP_ASSIGN_DEV_IRQ: case KVM_CAP_IRQFD: + case KVM_CAP_IOEVENTFD: case KVM_CAP_PIT2: r = 1; break; diff --git a/include/linux/kvm.h b/include/linux/kvm.h index 76c6408..22d0eb7 100644 --- a/include/linux/kvm.h +++ b/include/linux/kvm.h @@ -307,6 +307,28 @@ struct kvm_guest_debug { struct kvm_guest_debug_arch arch; }; +enum { + kvm_ioeventfd_flag_nr_datamatch, + kvm_ioeventfd_flag_nr_pio, + kvm_ioeventfd_flag_nr_deassign, + kvm_ioeventfd_flag_nr_max, +}; + +#define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch) +#define KVM_IOEVENTFD_FLAG_PIO (1 << kvm_ioeventfd_flag_nr_pio) +#define KVM_IOEVENTFD_FLAG_DEASSIGN (1 << kvm_ioeventfd_flag_nr_deassign) + +#define KVM_IOEVENTFD_VALID_FLAG_MASK ((1 << kvm_ioeventfd_flag_nr_max) - 1) + +struct kvm_ioeventfd { + __u64 datamatch; + __u64 addr; /* legal pio/mmio address */ + __u32 len; /* 1, 2, 4, or 8 bytes */ + __s32 fd; + __u32 flags; + __u8 pad[36]; +}; + #define KVM_TRC_SHIFT 16 /* * kvm trace categories @@ -409,6 +431,7 @@ struct kvm_guest_debug { #define KVM_CAP_PIT2 33 #endif #define KVM_CAP_SET_BOOT_CPU_ID 34 +#define KVM_CAP_IOEVENTFD 35 #ifdef KVM_CAP_IRQ_ROUTING @@ -517,6 +540,7 @@ struct kvm_irqfd { #define KVM_IRQFD _IOW(KVMIO, 0x76, struct kvm_irqfd) #define KVM_CREATE_PIT2 _IOW(KVMIO, 0x77, struct kvm_pit_config) #define KVM_SET_BOOT_CPU_ID _IO(KVMIO, 0x78) +#define KVM_IOEVENTFD _IOW(KVMIO, 0x79, struct kvm_ioeventfd) /* * ioctls for vcpu fds diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 306bc67..0347d59 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -154,6 +154,7 @@ struct kvm { spinlock_t lock; struct list_head items; } irqfds; + struct list_head ioeventfds; #endif struct kvm_vm_stat stat; struct kvm_arch arch; @@ -532,19 +533,24 @@ static inline void kvm_free_irq_routing(struct kvm *kvm) {} #ifdef CONFIG_HAVE_KVM_EVENTFD -void kvm_irqfd_init(struct kvm *kvm); +void kvm_eventfd_init(struct kvm *kvm); int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags); void kvm_irqfd_release(struct kvm *kvm); +int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args); #else -static inline void kvm_irqfd_init(struct kvm *kvm) {} +static inline void kvm_eventfd_init(struct kvm *kvm) {} static inline int kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags) { return -EINVAL; } static inline void kvm_irqfd_release(struct kvm *kvm) {} +static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) +{ + return -ENOSYS; +} #endif /* CONFIG_HAVE_KVM_EVENTFD */ diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c index 4092b8d..eee8edb 100644 --- a/virt/kvm/eventfd.c +++ b/virt/kvm/eventfd.c @@ -21,6 +21,7 @@ */ #include <linux/kvm_host.h> +#include <linux/kvm.h> #include <linux/workqueue.h> #include <linux/syscalls.h> #include <linux/wait.h> @@ -28,6 +29,9 @@ #include <linux/file.h> #include <linux/list.h> #include <linux/eventfd.h> +#include <linux/kernel.h> + +#include "iodev.h" /* * -------------------------------------------------------------------- @@ -234,10 +238,11 @@ fail: } void -kvm_irqfd_init(struct kvm *kvm) +kvm_eventfd_init(struct kvm *kvm) { spin_lock_init(&kvm->irqfds.lock); INIT_LIST_HEAD(&kvm->irqfds.items); + INIT_LIST_HEAD(&kvm->ioeventfds); } /* @@ -327,3 +332,248 @@ static void __exit irqfd_module_exit(void) module_init(irqfd_module_init); module_exit(irqfd_module_exit); + +/* + * -------------------------------------------------------------------- + * ioeventfd: translate a PIO/MMIO memory write to an eventfd signal. + * + * userspace can register a PIO/MMIO address with an eventfd for receiving + * notification when the memory has been touched. + * -------------------------------------------------------------------- + */ + +struct _ioeventfd { + struct list_head list; + u64 addr; + int length; + struct eventfd_ctx *eventfd; + u64 datamatch; + struct kvm_io_device dev; + bool wildcard; +}; + +static inline struct _ioeventfd * +to_ioeventfd(struct kvm_io_device *dev) +{ + return container_of(dev, struct _ioeventfd, dev); +} + +static void +ioeventfd_release(struct _ioeventfd *p) +{ + eventfd_ctx_put(p->eventfd); + list_del(&p->list); + kfree(p); +} + +static bool +ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val) +{ + u64 _val; + + if (!(addr == p->addr && len == p->length)) + /* address-range must be precise for a hit */ + return false; + + if (p->wildcard) + /* all else equal, wildcard is always a hit */ + return true; + + /* otherwise, we have to actually compare the data */ + + BUG_ON(!IS_ALIGNED((unsigned long)val, len)); + + switch (len) { + case 1: + _val = *(u8 *)val; + break; + case 2: + _val = *(u16 *)val; + break; + case 4: + _val = *(u32 *)val; + break; + case 8: + _val = *(u64 *)val; + break; + default: + return false; + } + + return _val == p->datamatch ? true : false; +} + +/* MMIO/PIO writes trigger an event if the addr/val match */ +static int +ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len, + const void *val) +{ + struct _ioeventfd *p = to_ioeventfd(this); + + if (!ioeventfd_in_range(p, addr, len, val)) + return -EOPNOTSUPP; + + eventfd_signal(p->eventfd, 1); + return 0; +} + +/* + * This function is called as KVM is completely shutting down. We do not + * need to worry about locking just nuke anything we have as quickly as possible + */ +static void +ioeventfd_destructor(struct kvm_io_device *this) +{ + struct _ioeventfd *p = to_ioeventfd(this); + + ioeventfd_release(p); +} + +static const struct kvm_io_device_ops ioeventfd_ops = { + .write = ioeventfd_write, + .destructor = ioeventfd_destructor, +}; + +/* assumes kvm->slots_lock held */ +static bool +ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p) +{ + struct _ioeventfd *_p; + + list_for_each_entry(_p, &kvm->ioeventfds, list) + if (_p->addr == p->addr && _p->length == p->length && + (_p->wildcard || p->wildcard || + _p->datamatch == p->datamatch)) + return true; + + return false; +} + +static int +kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) +{ + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; + struct _ioeventfd *p; + struct eventfd_ctx *eventfd; + int ret; + + /* must be natural-word sized */ + switch (args->len) { + case 1: + case 2: + case 4: + case 8: + break; + default: + return -EINVAL; + } + + /* check for range overflow */ + if (args->addr + args->len < args->addr) + return -EINVAL; + + /* check for extra flags that we don't understand */ + if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK) + return -EINVAL; + + eventfd = eventfd_ctx_fdget(args->fd); + if (IS_ERR(eventfd)) + return PTR_ERR(eventfd); + + p = kzalloc(sizeof(*p), GFP_KERNEL); + if (!p) { + ret = -ENOMEM; + goto fail; + } + + INIT_LIST_HEAD(&p->list); + p->addr = args->addr; + p->length = args->len; + p->eventfd = eventfd; + + /* The datamatch feature is optional, otherwise this is a wildcard */ + if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH) + p->datamatch = args->datamatch; + else + p->wildcard = true; + + down_write(&kvm->slots_lock); + + /* Verify that there isnt a match already */ + if (ioeventfd_check_collision(kvm, p)) { + ret = -EEXIST; + goto unlock_fail; + } + + kvm_iodevice_init(&p->dev, &ioeventfd_ops); + + ret = __kvm_io_bus_register_dev(bus, &p->dev); + if (ret < 0) + goto unlock_fail; + + list_add_tail(&p->list, &kvm->ioeventfds); + + up_write(&kvm->slots_lock); + + return 0; + +unlock_fail: + up_write(&kvm->slots_lock); + +fail: + kfree(p); + eventfd_ctx_put(eventfd); + + return ret; +} + +static int +kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) +{ + int pio = args->flags & KVM_IOEVENTFD_FLAG_PIO; + struct kvm_io_bus *bus = pio ? &kvm->pio_bus : &kvm->mmio_bus; + struct _ioeventfd *p, *tmp; + struct eventfd_ctx *eventfd; + int ret = -ENOENT; + + eventfd = eventfd_ctx_fdget(args->fd); + if (IS_ERR(eventfd)) + return PTR_ERR(eventfd); + + down_write(&kvm->slots_lock); + + list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) { + bool wildcard = args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH ? + true : false; + + if (p->eventfd != eventfd || + p->addr != args->addr || + p->length != args->len || + p->wildcard != wildcard) + continue; + + if (!p->wildcard && p->datamatch != args->datamatch) + continue; + + __kvm_io_bus_unregister_dev(bus, &p->dev); + ioeventfd_release(p); + ret = 0; + break; + } + + up_write(&kvm->slots_lock); + + eventfd_ctx_put(eventfd); + + return ret; +} + +int +kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args) +{ + if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN) + return kvm_deassign_ioeventfd(kvm, args); + + return kvm_assign_ioeventfd(kvm, args); +} diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index dd92b44..14e1f32 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -979,7 +979,7 @@ static struct kvm *kvm_create_vm(void) spin_lock_init(&kvm->mmu_lock); spin_lock_init(&kvm->requests_lock); kvm_io_bus_init(&kvm->pio_bus); - kvm_irqfd_init(kvm); + kvm_eventfd_init(kvm); mutex_init(&kvm->lock); mutex_init(&kvm->irq_lock); kvm_io_bus_init(&kvm->mmio_bus); @@ -2271,6 +2271,15 @@ static long kvm_vm_ioctl(struct file *filp, r = kvm_irqfd(kvm, data.fd, data.gsi, data.flags); break; } + case KVM_IOEVENTFD: { + struct kvm_ioeventfd data; + + r = -EFAULT; + if (copy_from_user(&data, argp, sizeof data)) + goto out; + r = kvm_ioeventfd(kvm, &data); + break; + } #ifdef CONFIG_KVM_APIC_ARCHITECTURE case KVM_SET_BOOT_CPU_ID: r = 0;
ioeventfd is a mechanism to register PIO/MMIO regions to trigger an eventfd signal when written to by a guest. Host userspace can register any arbitrary IO address with a corresponding eventfd and then pass the eventfd to a specific end-point of interest for handling. Normal IO requires a blocking round-trip since the operation may cause side-effects in the emulated model or may return data to the caller. Therefore, an IO in KVM traps from the guest to the host, causes a VMX/SVM "heavy-weight" exit back to userspace, and is ultimately serviced by qemu's device model synchronously before returning control back to the vcpu. However, there is a subclass of IO which acts purely as a trigger for other IO (such as to kick off an out-of-band DMA request, etc). For these patterns, the synchronous call is particularly expensive since we really only want to simply get our notification transmitted asychronously and return as quickly as possible. All the sychronous infrastructure to ensure proper data-dependencies are met in the normal IO case are just unecessary overhead for signalling. This adds additional computational load on the system, as well as latency to the signalling path. Therefore, we provide a mechanism for registration of an in-kernel trigger point that allows the VCPU to only require a very brief, lightweight exit just long enough to signal an eventfd. This also means that any clients compatible with the eventfd interface (which includes userspace and kernelspace equally well) can now register to be notified. The end result should be a more flexible and higher performance notification API for the backend KVM hypervisor and perhipheral components. To test this theory, we built a test-harness called "doorbell". This module has a function called "doorbell_ring()" which simply increments a counter for each time the doorbell is signaled. It supports signalling from either an eventfd, or an ioctl(). We then wired up two paths to the doorbell: One via QEMU via a registered io region and through the doorbell ioctl(). The other is direct via ioeventfd. You can download this test harness here: ftp://ftp.novell.com/dev/ghaskins/doorbell.tar.bz2 The measured results are as follows: qemu-mmio: 110000 iops, 9.09us rtt ioeventfd-mmio: 200100 iops, 5.00us rtt ioeventfd-pio: 367300 iops, 2.72us rtt I didn't measure qemu-pio, because I have to figure out how to register a PIO region with qemu's device model, and I got lazy. However, for now we can extrapolate based on the data from the NULLIO runs of +2.56us for MMIO, and -350ns for HC, we get: qemu-pio: 153139 iops, 6.53us rtt ioeventfd-hc: 412585 iops, 2.37us rtt these are just for fun, for now, until I can gather more data. Here is a graph for your convenience: http://developer.novell.com/wiki/images/7/76/Iofd-chart.png The conclusion to draw is that we save about 4us by skipping the userspace hop. -------------------- Signed-off-by: Gregory Haskins <ghaskins@novell.com> --- arch/x86/kvm/x86.c | 1 include/linux/kvm.h | 24 ++++ include/linux/kvm_host.h | 10 +- virt/kvm/eventfd.c | 252 ++++++++++++++++++++++++++++++++++++++++++++++ virt/kvm/kvm_main.c | 11 ++ 5 files changed, 294 insertions(+), 4 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html