On 2017/7/31 21:22, Christoffer Dall wrote: > On Sat, Jul 29, 2017 at 02:22:57PM +0800, Longpeng(Mike) wrote: >> We had disscuss the idea here: >> https://www.spinics.net/lists/kvm/msg140593.html > > This is not a very nice way to start a commit description. > > Please provide the necessary background to understand your change > directly in the commit message. > >> >> I think it's also suitable for other architectures. >> > > I think this sentence can go in the end of the commit message together > with your explanation of only doing this for x86. > OK :) > By the way, the ARM solution should be pretty simple: > > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c > index a39a1e1..b9f68e4 100644 > --- a/virt/kvm/arm/arm.c > +++ b/virt/kvm/arm/arm.c > @@ -416,6 +416,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v) > && !v->arch.power_off && !v->arch.pause); > } > > +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu) > +{ > + return vcpu_mode_priv(vcpu); > +} > + > /* Just ensure a guest exit from a particular CPU */ > static void exit_vm_noop(void *info) > { > > > I am also curious in the workload you use to measure this and how I can > evaluate the benefit on ARM? > We had tested this using the SpecVirt testsuite, no improvement (no decrease at least) because of the spinlock isn't the major factor of this testsuite. Currently I haven't any performance numbers to prove the patch is make sense, but I'll do some tests later. > Thanks, > -Christoffer > >> If the vcpu(me) exit due to request a usermode spinlock, then >> the spinlock-holder may be preempted in usermode or kernmode. >> But if the vcpu(me) is in kernmode, then the holder must be >> preempted in kernmode, so we should choose a vcpu in kernmode >> as the most eligible candidate. >> >> PS: I only implement X86 arch currently for I'm not familiar >> with other architecture. >> >> Signed-off-by: Longpeng(Mike) <longpeng2@xxxxxxxxxx> >> --- >> arch/mips/kvm/mips.c | 5 +++++ >> arch/powerpc/kvm/powerpc.c | 5 +++++ >> arch/s390/kvm/kvm-s390.c | 5 +++++ >> arch/x86/kvm/x86.c | 5 +++++ >> include/linux/kvm_host.h | 4 ++++ >> virt/kvm/arm/arm.c | 5 +++++ >> virt/kvm/kvm_main.c | 9 ++++++++- >> 7 files changed, 37 insertions(+), 1 deletion(-) >> >> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c >> index d4b2ad1..2e2701d 100644 >> --- a/arch/mips/kvm/mips.c >> +++ b/arch/mips/kvm/mips.c >> @@ -98,6 +98,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) >> return !!(vcpu->arch.pending_exceptions); >> } >> >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu) >> +{ >> + return false; >> +} >> + >> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu) >> { >> return 1; >> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c >> index 1a75c0b..2489f64 100644 >> --- a/arch/powerpc/kvm/powerpc.c >> +++ b/arch/powerpc/kvm/powerpc.c >> @@ -58,6 +58,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v) >> return !!(v->arch.pending_exceptions) || kvm_request_pending(v); >> } >> >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu) >> +{ >> + return false; >> +} >> + >> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu) >> { >> return 1; >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 3f2884e..9d7c42e 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -2443,6 +2443,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) >> return kvm_s390_vcpu_has_irq(vcpu, 0); >> } >> >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu) >> +{ >> + return false; >> +} >> + >> void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu) >> { >> atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20); >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 82a63c5..b5a2e53 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -8435,6 +8435,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu) >> return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu); >> } >> >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu) >> +{ >> + return kvm_x86_ops->get_cpl(vcpu) == 0; >> +} >> + >> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu) >> { >> return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE; >> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >> index 648b34c..f8f0d74 100644 >> --- a/include/linux/kvm_host.h >> +++ b/include/linux/kvm_host.h >> @@ -272,6 +272,9 @@ struct kvm_vcpu { >> } spin_loop; >> #endif >> bool preempted; >> + /* If vcpu is in kernel-mode when preempted */ >> + bool in_kernmode; >> + >> struct kvm_vcpu_arch arch; >> struct dentry *debugfs_dentry; >> }; >> @@ -797,6 +800,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu, >> void kvm_arch_hardware_unsetup(void); >> void kvm_arch_check_processor_compat(void *rtn); >> int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu); >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu); >> int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu); >> >> #ifndef __KVM_HAVE_ARCH_VM_ALLOC >> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c >> index a39a1e1..ca6a394 100644 >> --- a/virt/kvm/arm/arm.c >> +++ b/virt/kvm/arm/arm.c >> @@ -416,6 +416,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v) >> && !v->arch.power_off && !v->arch.pause); >> } >> >> +bool kvm_arch_vcpu_spin_kernmode(struct kvm_vcpu *vcpu) >> +{ >> + return false; >> +} >> + >> /* Just ensure a guest exit from a particular CPU */ >> static void exit_vm_noop(void *info) >> { >> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >> index 82987d4..8d83caa 100644 >> --- a/virt/kvm/kvm_main.c >> +++ b/virt/kvm/kvm_main.c >> @@ -290,6 +290,7 @@ int kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id) >> kvm_vcpu_set_in_spin_loop(vcpu, false); >> kvm_vcpu_set_dy_eligible(vcpu, false); >> vcpu->preempted = false; >> + vcpu->in_kernmode = false; >> >> r = kvm_arch_vcpu_init(vcpu); >> if (r < 0) >> @@ -2330,6 +2331,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) >> int pass; >> int i; >> >> + me->in_kernmode = kvm_arch_vcpu_spin_kernmode(me); >> kvm_vcpu_set_in_spin_loop(me, true); >> /* >> * We boost the priority of a VCPU that is runnable but not >> @@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) >> continue; >> if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu)) >> continue; >> + if (me->in_kernmode && !vcpu->in_kernmode) >> + continue; >> if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) >> continue; >> >> @@ -4009,8 +4013,11 @@ static void kvm_sched_out(struct preempt_notifier *pn, >> { >> struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); >> >> - if (current->state == TASK_RUNNING) >> + if (current->state == TASK_RUNNING) { >> vcpu->preempted = true; >> + vcpu->in_kernmode = kvm_arch_vcpu_spin_kernmode(vcpu); >> + } >> + >> kvm_arch_vcpu_put(vcpu); >> } >> >> -- >> 1.8.3.1 >> >> > > . > -- Regards, Longpeng(Mike)
