diff options
| author | Michael S. Tsirkin <mst@redhat.com> | 2013-11-04 22:36:25 +0200 |
|---|---|---|
| committer | Gleb Natapov <gleb@redhat.com> | 2013-11-06 09:32:31 +0200 |
| commit | 01b71917b55d28c09ade9fb8c683cf0d2aad1858 (patch) | |
| tree | 5ec0842876cd80c754c486dac1a810850d98ecd6 /arch/x86/kvm | |
| parent | ce332f662deb545c8a4f3f58debcca26bb2e44b0 (diff) | |
| download | linux-01b71917b55d28c09ade9fb8c683cf0d2aad1858.tar.bz2 | |
kvm: optimize out smp_mb after srcu_read_unlock
I noticed that srcu_read_lock/unlock both have a memory barrier,
so just by moving srcu_read_unlock earlier we can get rid of
one call to smp_mb() using smp_mb__after_srcu_read_unlock instead.
Unsurprisingly, the gain is small but measureable using the unit test
microbenchmark:
before
vmcall in the ballpark of 1410 cycles
after
vmcall in the ballpark of 1360 cycles
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
| -rw-r--r-- | arch/x86/kvm/x86.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 07c127fc2064..21ef1ba184ae 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5966,10 +5966,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) vcpu->mode = IN_GUEST_MODE; + srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); + /* We should set ->mode before check ->requests, * see the comment in make_all_cpus_request. */ - smp_mb(); + smp_mb__after_srcu_read_unlock(); local_irq_disable(); @@ -5979,12 +5981,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) smp_wmb(); local_irq_enable(); preempt_enable(); + vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu); r = 1; goto cancel_injection; } - srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx); - if (req_immediate_exit) smp_send_reschedule(vcpu->cpu); |