| Message ID | 20210317221940.2146688-4-jason@jlekstrand.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | dma-buf: Add an API for exporting sync files (v8) | expand |
Adding mesa-dev and wayland-devel for broader circulation. On Wed, Mar 17, 2021 at 5:19 PM Jason Ekstrand <jason@jlekstrand.net> wrote: > > Modern userspace APIs like Vulkan are built on an explicit > synchronization model. This doesn't always play nicely with the > implicit synchronization used in the kernel and assumed by X11 and > Wayland. The client -> compositor half of the synchronization isn't too > bad, at least on intel, because we can control whether or not i915 > synchronizes on the buffer and whether or not it's considered written. > > The harder part is the compositor -> client synchronization when we get > the buffer back from the compositor. We're required to be able to > provide the client with a VkSemaphore and VkFence representing the point > in time where the window system (compositor and/or display) finished > using the buffer. With current APIs, it's very hard to do this in such > a way that we don't get confused by the Vulkan driver's access of the > buffer. In particular, once we tell the kernel that we're rendering to > the buffer again, any CPU waits on the buffer or GPU dependencies will > wait on some of the client rendering and not just the compositor. > > This new IOCTL solves this problem by allowing us to get a snapshot of > the implicit synchronization state of a given dma-buf in the form of a > sync file. It's effectively the same as a poll() or I915_GEM_WAIT only, > instead of CPU waiting directly, it encapsulates the wait operation, at > the current moment in time, in a sync_file so we can check/wait on it > later. As long as the Vulkan driver does the sync_file export from the > dma-buf before we re-introduce it for rendering, it will only contain > fences from the compositor or display. This allows to accurately turn > it into a VkFence or VkSemaphore without any over- synchronization. > > v2 (Jason Ekstrand): > - Use a wrapper dma_fence_array of all fences including the new one > when importing an exclusive fence. > > v3 (Jason Ekstrand): > - Lock around setting shared fences as well as exclusive > - Mark SIGNAL_SYNC_FILE as a read-write ioctl. > - Initialize ret to 0 in dma_buf_wait_sync_file > > v4 (Jason Ekstrand): > - Use the new dma_resv_get_singleton helper > > v5 (Jason Ekstrand): > - Rename the IOCTLs to import/export rather than wait/signal > - Drop the WRITE flag and always get/set the exclusive fence > > v6 (Jason Ekstrand): > - Drop the sync_file import as it was all-around sketchy and not nearly > as useful as import. > - Re-introduce READ/WRITE flag support for export > - Rework the commit message > > v7 (Jason Ekstrand): > - Require at least one sync flag > - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference > - Use _rcu helpers since we're accessing the dma_resv read-only > > v8 (Jason Ekstrand): > - Return -ENOMEM if the sync_file_create fails > - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE) > > Signed-off-by: Jason Ekstrand <jason@jlekstrand.net> > --- > drivers/dma-buf/dma-buf.c | 62 ++++++++++++++++++++++++++++++++++++ > include/uapi/linux/dma-buf.h | 6 ++++ > 2 files changed, 68 insertions(+) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index f264b70c383eb..a5e4b0b6a049c 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -20,6 +20,7 @@ > #include <linux/debugfs.h> > #include <linux/module.h> > #include <linux/seq_file.h> > +#include <linux/sync_file.h> > #include <linux/poll.h> > #include <linux/dma-resv.h> > #include <linux/mm.h> > @@ -362,6 +363,62 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) > return ret; > } > > +#if IS_ENABLED(CONFIG_SYNC_FILE) > +static long dma_buf_export_sync_file(struct dma_buf *dmabuf, > + void __user *user_data) > +{ > + struct dma_buf_sync_file arg; > + struct dma_fence *fence = NULL; > + struct sync_file *sync_file; > + int fd, ret; > + > + if (copy_from_user(&arg, user_data, sizeof(arg))) > + return -EFAULT; > + > + if (arg.flags & ~DMA_BUF_SYNC_RW) > + return -EINVAL; > + > + if ((arg.flags & DMA_BUF_SYNC_RW) == 0) > + return -EINVAL; > + > + fd = get_unused_fd_flags(O_CLOEXEC); > + if (fd < 0) > + return fd; > + > + if (arg.flags & DMA_BUF_SYNC_WRITE) { > + ret = dma_resv_get_singleton_rcu(dmabuf->resv, &fence); > + if (ret) > + goto err_put_fd; > + } else if (arg.flags & DMA_BUF_SYNC_READ) { > + fence = dma_resv_get_excl_rcu(dmabuf->resv); > + } > + > + if (!fence) > + fence = dma_fence_get_stub(); > + > + sync_file = sync_file_create(fence); > + > + dma_fence_put(fence); > + > + if (!sync_file) { > + ret = -ENOMEM; > + goto err_put_fd; > + } > + > + fd_install(fd, sync_file->file); > + > + arg.fd = fd; > + if (copy_to_user(user_data, &arg, sizeof(arg))) > + return -EFAULT; > + > + return 0; > + > +err_put_fd: > + put_unused_fd(fd); > + return ret; > +} > +#endif > + > static long dma_buf_ioctl(struct file *file, > unsigned int cmd, unsigned long arg) > { > @@ -405,6 +462,11 @@ static long dma_buf_ioctl(struct file *file, > case DMA_BUF_SET_NAME_B: > return dma_buf_set_name(dmabuf, (const char __user *)arg); > > +#if IS_ENABLED(CONFIG_SYNC_FILE) > + case DMA_BUF_IOCTL_EXPORT_SYNC_FILE: > + return dma_buf_export_sync_file(dmabuf, (void __user *)arg); > +#endif > + > default: > return -ENOTTY; > } > diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h > index 7f30393b92c3b..9bce1e8bd31d3 100644 > --- a/include/uapi/linux/dma-buf.h > +++ b/include/uapi/linux/dma-buf.h > @@ -37,6 +37,11 @@ struct dma_buf_sync { > > #define DMA_BUF_NAME_LEN 32 > > +struct dma_buf_sync_file { > + __u32 flags; > + __s32 fd; > +}; > + > #define DMA_BUF_BASE 'b' > #define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) > > @@ -46,5 +51,6 @@ struct dma_buf_sync { > #define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *) > #define DMA_BUF_SET_NAME_A _IOW(DMA_BUF_BASE, 1, u32) > #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, u64) > +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_sync_file) > > #endif > -- > 2.29.2 >
From a user-space point-of-view, this looks super useful! The uAPI sounds
good to me.
Acked-by: Simon Ser <contact@emersion.fr>
Would be nice to have some short docs as well. Here's an example of a
patch adding some docs for an ioctl [1], if you aren't familiar with
that. I think just some basic stuff (description, which parameters are
in/out, what the flags are) would be great.
[1]: https://patchwork.freedesktop.org/patch/401951/
On Tue, Mar 23, 2021 at 2:06 PM Simon Ser <contact@emersion.fr> wrote: > > From a user-space point-of-view, this looks super useful! The uAPI sounds > good to me. > > Acked-by: Simon Ser <contact@emersion.fr> > > Would be nice to have some short docs as well. Here's an example of a > patch adding some docs for an ioctl [1], if you aren't familiar with > that. I think just some basic stuff (description, which parameters are > in/out, what the flags are) would be great. Good call. v9 will have docs. --Jason
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index f264b70c383eb..a5e4b0b6a049c 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -20,6 +20,7 @@ #include <linux/debugfs.h> #include <linux/module.h> #include <linux/seq_file.h> +#include <linux/sync_file.h> #include <linux/poll.h> #include <linux/dma-resv.h> #include <linux/mm.h> @@ -362,6 +363,62 @@ static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf) return ret; } +#if IS_ENABLED(CONFIG_SYNC_FILE) +static long dma_buf_export_sync_file(struct dma_buf *dmabuf, + void __user *user_data) +{ + struct dma_buf_sync_file arg; + struct dma_fence *fence = NULL; + struct sync_file *sync_file; + int fd, ret; + + if (copy_from_user(&arg, user_data, sizeof(arg))) + return -EFAULT; + + if (arg.flags & ~DMA_BUF_SYNC_RW) + return -EINVAL; + + if ((arg.flags & DMA_BUF_SYNC_RW) == 0) + return -EINVAL; + + fd = get_unused_fd_flags(O_CLOEXEC); + if (fd < 0) + return fd; + + if (arg.flags & DMA_BUF_SYNC_WRITE) { + ret = dma_resv_get_singleton_rcu(dmabuf->resv, &fence); + if (ret) + goto err_put_fd; + } else if (arg.flags & DMA_BUF_SYNC_READ) { + fence = dma_resv_get_excl_rcu(dmabuf->resv); + } + + if (!fence) + fence = dma_fence_get_stub(); + + sync_file = sync_file_create(fence); + + dma_fence_put(fence); + + if (!sync_file) { + ret = -ENOMEM; + goto err_put_fd; + } + + fd_install(fd, sync_file->file); + + arg.fd = fd; + if (copy_to_user(user_data, &arg, sizeof(arg))) + return -EFAULT; + + return 0; + +err_put_fd: + put_unused_fd(fd); + return ret; +} +#endif + static long dma_buf_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { @@ -405,6 +462,11 @@ static long dma_buf_ioctl(struct file *file, case DMA_BUF_SET_NAME_B: return dma_buf_set_name(dmabuf, (const char __user *)arg); +#if IS_ENABLED(CONFIG_SYNC_FILE) + case DMA_BUF_IOCTL_EXPORT_SYNC_FILE: + return dma_buf_export_sync_file(dmabuf, (void __user *)arg); +#endif + default: return -ENOTTY; } diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma-buf.h index 7f30393b92c3b..9bce1e8bd31d3 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -37,6 +37,11 @@ struct dma_buf_sync { #define DMA_BUF_NAME_LEN 32 +struct dma_buf_sync_file { + __u32 flags; + __s32 fd; +}; + #define DMA_BUF_BASE 'b' #define DMA_BUF_IOCTL_SYNC _IOW(DMA_BUF_BASE, 0, struct dma_buf_sync) @@ -46,5 +51,6 @@ struct dma_buf_sync { #define DMA_BUF_SET_NAME _IOW(DMA_BUF_BASE, 1, const char *) #define DMA_BUF_SET_NAME_A _IOW(DMA_BUF_BASE, 1, u32) #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, u64) +#define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_sync_file) #endif
Modern userspace APIs like Vulkan are built on an explicit synchronization model. This doesn't always play nicely with the implicit synchronization used in the kernel and assumed by X11 and Wayland. The client -> compositor half of the synchronization isn't too bad, at least on intel, because we can control whether or not i915 synchronizes on the buffer and whether or not it's considered written. The harder part is the compositor -> client synchronization when we get the buffer back from the compositor. We're required to be able to provide the client with a VkSemaphore and VkFence representing the point in time where the window system (compositor and/or display) finished using the buffer. With current APIs, it's very hard to do this in such a way that we don't get confused by the Vulkan driver's access of the buffer. In particular, once we tell the kernel that we're rendering to the buffer again, any CPU waits on the buffer or GPU dependencies will wait on some of the client rendering and not just the compositor. This new IOCTL solves this problem by allowing us to get a snapshot of the implicit synchronization state of a given dma-buf in the form of a sync file. It's effectively the same as a poll() or I915_GEM_WAIT only, instead of CPU waiting directly, it encapsulates the wait operation, at the current moment in time, in a sync_file so we can check/wait on it later. As long as the Vulkan driver does the sync_file export from the dma-buf before we re-introduce it for rendering, it will only contain fences from the compositor or display. This allows to accurately turn it into a VkFence or VkSemaphore without any over- synchronization. v2 (Jason Ekstrand): - Use a wrapper dma_fence_array of all fences including the new one when importing an exclusive fence. v3 (Jason Ekstrand): - Lock around setting shared fences as well as exclusive - Mark SIGNAL_SYNC_FILE as a read-write ioctl. - Initialize ret to 0 in dma_buf_wait_sync_file v4 (Jason Ekstrand): - Use the new dma_resv_get_singleton helper v5 (Jason Ekstrand): - Rename the IOCTLs to import/export rather than wait/signal - Drop the WRITE flag and always get/set the exclusive fence v6 (Jason Ekstrand): - Drop the sync_file import as it was all-around sketchy and not nearly as useful as import. - Re-introduce READ/WRITE flag support for export - Rework the commit message v7 (Jason Ekstrand): - Require at least one sync flag - Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference - Use _rcu helpers since we're accessing the dma_resv read-only v8 (Jason Ekstrand): - Return -ENOMEM if the sync_file_create fails - Predicate support on IS_ENABLED(CONFIG_SYNC_FILE) Signed-off-by: Jason Ekstrand <jason@jlekstrand.net> --- drivers/dma-buf/dma-buf.c | 62 ++++++++++++++++++++++++++++++++++++ include/uapi/linux/dma-buf.h | 6 ++++ 2 files changed, 68 insertions(+)