On Thu, Nov 02, 2017 at 06:56:46PM +0100, Paolo Bonzini wrote: > On 02/11/2017 18:45, Eduardo Valentin wrote: > > 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. > > Have you seen Waiman's series that lets you specify this on the guest > command line instead? Would this be acceptable for your use case? > No, can you please share a link to it? is it already merged to tip/master? > (In other words, is there a difference for you between making the host > vs. guest administrator toggle the feature? "@amazon.com" means you are > the host admin, how would you use it?) > The way I think of this is this is a flag set by host side so the guest adapts accordingly. If the admin in guest side wants to ignore what the host is flagging, that is a different story. > Thanks, > > Paolo > > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx> > > Cc: Jonathan Corbet <corbet@xxxxxxx> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > > Cc: x86@xxxxxxxxxx > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > > Cc: Waiman Long <longman@xxxxxxxxxx> > > Cc: kvm@xxxxxxxxxxxxxxx > > Cc: linux-doc@xxxxxxxxxxxxxxx > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > Cc: Jan H. Schoenherr <jschoenh@xxxxxxxxx> > > Cc: Anthony Liguori <aliguori@xxxxxxxxxx> > > Suggested-by: Matt Wilson <msw@xxxxxxxxxx> > > Signed-off-by: Eduardo Valentin <eduval@xxxxxxxxxx> > > --- > > V2: > > - rebase on top of tip/master > > > > 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(+) > > > > 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 308dfd0..3751898 100644 > > --- a/arch/x86/include/asm/qspinlock.h > > +++ b/arch/x86/include/asm/qspinlock.h > > @@ -2,6 +2,8 @@ > > #define _ASM_X86_QSPINLOCK_H > > > > #include <linux/jump_label.h> > > +#include <linux/kvm_para.h> > > + > > #include <asm/cpufeature.h> > > #include <asm-generic/qspinlock_types.h> > > #include <asm/paravirt.h> > > @@ -57,6 +59,8 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > > if (!static_branch_likely(&virt_spin_lock_key)) > > 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 a965e5b0..d151300 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. > > > > -- All the best, Eduardo Valentin
