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KVM: Get rid of KVM_REQ_KICK

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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.

Fix by replacing KVM_REQ_KICK with a vcpu->guest_mode atomic.

Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Avi Kivity 2010-05-03 16:54:48 +03:00
commit d94e1dc9af
2 changed files with 11 additions and 7 deletions
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17
arch/x86/kvm/x86.c
View file

@ -4604,13 +4604,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (vcpu->fpu_active) if (vcpu->fpu_active)
kvm_load_guest_fpu(vcpu); kvm_load_guest_fpu(vcpu);
atomic_set(&vcpu->guest_mode, 1);
smp_wmb();
local_irq_disable(); local_irq_disable();
clear_bit(KVM_REQ_KICK, &vcpu->requests); if (!atomic_read(&vcpu->guest_mode) || vcpu->requests
smp_mb__after_clear_bit(); || need_resched() || signal_pending(current)) {
atomic_set(&vcpu->guest_mode, 0);
if (vcpu->requests || need_resched() || signal_pending(current)) { smp_wmb();
set_bit(KVM_REQ_KICK, &vcpu->requests);
local_irq_enable(); local_irq_enable();
preempt_enable(); preempt_enable();
r = 1; r = 1;
@ -4655,7 +4657,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (hw_breakpoint_active()) if (hw_breakpoint_active())
hw_breakpoint_restore(); hw_breakpoint_restore();
set_bit(KVM_REQ_KICK, &vcpu->requests); atomic_set(&vcpu->guest_mode, 0);
smp_wmb();
local_irq_enable(); local_irq_enable();
++vcpu->stat.exits; ++vcpu->stat.exits;
@ -5580,7 +5583,7 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
me = get_cpu(); me = get_cpu();
if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(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); smp_send_reschedule(cpu);
put_cpu(); put_cpu();
} }

1
include/linux/kvm_host.h
View file

@ -81,6 +81,7 @@ struct kvm_vcpu {
int vcpu_id; int vcpu_id;
struct mutex mutex; struct mutex mutex;
int cpu; int cpu;
atomic_t guest_mode;
struct kvm_run *run; struct kvm_run *run;
unsigned long requests; unsigned long requests;
unsigned long guest_debug; unsigned long guest_debug;