On Mon, May 03, 2010 at 05:19:08PM +0300, Avi Kivity wrote: > KVM_REQ_KICK poisons vcpu->requests by having a bit set during normal > operation. This causes the fast path check for a clear vcpu->requests > to fail all the time, triggering tons of atomic operations.
Avi, Do you have numbers? > Fix by replacing KVM_REQ_KICK with a vcpu->guest_mode atomic. > > Signed-off-by: Avi Kivity <[email protected]> > --- > arch/x86/kvm/x86.c | 17 ++++++++++------- > include/linux/kvm_host.h | 1 + > 2 files changed, 11 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 6b2ce1d..307094a 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4499,13 +4499,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > if (vcpu->fpu_active) > kvm_load_guest_fpu(vcpu); > > - local_irq_disable(); > + atomic_set(&vcpu->guest_mode, 1); > + smp_wmb(); IPI can trigger here? > - clear_bit(KVM_REQ_KICK, &vcpu->requests); > - smp_mb__after_clear_bit(); > + local_irq_disable(); > > - if (vcpu->requests || need_resched() || signal_pending(current)) { > - set_bit(KVM_REQ_KICK, &vcpu->requests); > + if (!atomic_read(&vcpu->guest_mode) || vcpu->requests > + || need_resched() || signal_pending(current)) { > + atomic_set(&vcpu->guest_mode, 0); > + smp_wmb(); > local_irq_enable(); > preempt_enable(); > r = 1; > @@ -4550,7 +4552,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > if (hw_breakpoint_active()) > hw_breakpoint_restore(); > > - set_bit(KVM_REQ_KICK, &vcpu->requests); > + atomic_set(&vcpu->guest_mode, 0); > + smp_wmb(); > local_irq_enable(); > > ++vcpu->stat.exits; > @@ -5470,7 +5473,7 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu) > > me = get_cpu(); > if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) > - if (!test_and_set_bit(KVM_REQ_KICK, &vcpu->requests)) > + if (atomic_xchg(&vcpu->guest_mode, 0)) > smp_send_reschedule(cpu); > put_cpu(); > } > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index ce027d5..a020fa2 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -81,6 +81,7 @@ struct kvm_vcpu { > int vcpu_id; > struct mutex mutex; > int cpu; > + atomic_t guest_mode; > struct kvm_run *run; > unsigned long requests; > unsigned long guest_debug; > -- > 1.7.0.4 > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
