| Message ID | 1508805867-14583-1-git-send-email-eduval@amazon.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, Oct 23, 2017 at 05:44:27PM -0700, Eduardo Valentin wrote: > @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) > return false; > > + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) > + return false; > /* > * On hypervisors without PARAVIRT_SPINLOCKS support we fall > * back to a Test-and-Set spinlock, because fair locks have This does not apply. Much has been changed here recently.
2017-10-23 17:44-0700, Eduardo Valentin: > Currently, the existing qspinlock implementation will fallback to > test-and-set if the hypervisor has not set the PV_UNHALT flag. Where have you detected the main source of overhead with pinned VCPUs? Makes me wonder if we couldn't improve general PV_UNHALT, thanks. > This patch gives the opportunity to guest kernels to select > between test-and-set and the regular queueu fair lock implementation > based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED > flag is not set, the code will still fall back to test-and-set, > but when the PV_DEDICATED flag is set, the code will use > the regular queue spinlock implementation. Some flag makes sense and we do want to make sure that userspaces don't enable it in pass-through-cpuid mode.
Hello Peter, On Tue, Oct 24, 2017 at 10:13:45AM +0200, Peter Zijlstra wrote: > On Mon, Oct 23, 2017 at 05:44:27PM -0700, Eduardo Valentin wrote: > > @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > > if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) > > return false; > > > > + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) > > + return false; > > /* > > * On hypervisors without PARAVIRT_SPINLOCKS support we fall > > * back to a Test-and-Set spinlock, because fair locks have > > This does not apply. Much has been changed here recently. > I checked against Linus master branch before sending. Which tree/branch are you referring to / should I based this?
On 10/24/2017 11:37 AM, Eduardo Valentin wrote: > Hello Peter, > On Tue, Oct 24, 2017 at 10:13:45AM +0200, Peter Zijlstra wrote: >> On Mon, Oct 23, 2017 at 05:44:27PM -0700, Eduardo Valentin wrote: >>> @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) >>> if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) >>> return false; >>> >>> + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) >>> + return false; >>> /* >>> * On hypervisors without PARAVIRT_SPINLOCKS support we fall >>> * back to a Test-and-Set spinlock, because fair locks have >> This does not apply. Much has been changed here recently. >> > I checked against Linus master branch before sending. Which tree/branch are you referring to / should I based this? > Please check the tip tree (https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git) which has the latest changes in locking code. Cheers, Longman
Hey Waiman, On Tue, Oct 24, 2017 at 12:07:04PM -0400, Waiman Long wrote: > On 10/24/2017 11:37 AM, Eduardo Valentin wrote: > > Hello Peter, > > On Tue, Oct 24, 2017 at 10:13:45AM +0200, Peter Zijlstra wrote: > >> On Mon, Oct 23, 2017 at 05:44:27PM -0700, Eduardo Valentin wrote: > >>> @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > >>> if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) > >>> return false; > >>> > >>> + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) > >>> + return false; > >>> /* > >>> * On hypervisors without PARAVIRT_SPINLOCKS support we fall > >>> * back to a Test-and-Set spinlock, because fair locks have > >> This does not apply. Much has been changed here recently. > >> > > I checked against Linus master branch before sending. Which tree/branch are you referring to / should I based this? > > > Please check the tip tree > (https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git) which has > the latest changes in locking code. I will rebase the patch on top of the tip tree. Thanks. > > Cheers, > Longman >
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 3c65feb..117066a 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -54,6 +54,12 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit || || before enabling paravirtualized || || spinlock support. ------------------------------------------------------------------------------ +KVM_FEATURE_PV_DEDICATED || 8 || guest checks this feature bit + || || to determine if they run on + || || dedicated vCPUs, allowing opti- + || || mizations such as usage of + || || qspinlocks. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index eaba080..f89b469 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -1,6 +1,8 @@ #ifndef _ASM_X86_QSPINLOCK_H #define _ASM_X86_QSPINLOCK_H +#include <linux/kvm_para.h> + #include <asm/cpufeature.h> #include <asm-generic/qspinlock_types.h> #include <asm/paravirt.h> @@ -46,6 +48,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) return false; + if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) + return false; /* * On hypervisors without PARAVIRT_SPINLOCKS support we fall * back to a Test-and-Set spinlock, because fair locks have diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h index 94dc8ca..ad2e8fe 100644 --- a/arch/x86/include/uapi/asm/kvm_para.h +++ b/arch/x86/include/uapi/asm/kvm_para.h @@ -24,6 +24,7 @@ #define KVM_FEATURE_STEAL_TIME 5 #define KVM_FEATURE_PV_EOI 6 #define KVM_FEATURE_PV_UNHALT 7 +#define KVM_FEATURE_PV_DEDICATED 8 /* The last 8 bits are used to indicate how to interpret the flags field * in pvclock structure. If no bits are set, all flags are ignored.
Currently, the existing qspinlock implementation will fallback to test-and-set if the hypervisor has not set the PV_UNHALT flag. This patch gives the opportunity to guest kernels to select between test-and-set and the regular queueu fair lock implementation based on the PV_DEDICATED KVM feature flag. When the PV_DEDICATED flag is not set, the code will still fall back to test-and-set, but when the PV_DEDICATED flag is set, the code will use the regular queue spinlock implementation. Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: "Radim Krčmář" <rkrcmar@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: x86@kernel.org Cc: Peter Zijlstra <peterz@infradead.org> Cc: Waiman Long <longman@redhat.com> Cc: kvm@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: Jan H. Schoenherr <jschoenh@amazon.de> Cc: Anthony Liguori <aliguori@amazon.com> Suggested-by: Matt Wilson <msw@amazon.com> Signed-off-by: Eduardo Valentin <eduval@amazon.com> --- Documentation/virtual/kvm/cpuid.txt | 6 ++++++ arch/x86/include/asm/qspinlock.h | 4 ++++ arch/x86/include/uapi/asm/kvm_para.h | 1 + 3 files changed, 11 insertions(+)