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author | Rik van Riel <riel@redhat.com> | 2011-02-01 09:53:28 -0500 |
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committer | Marcelo Tosatti <mtosatti@redhat.com> | 2011-03-17 13:08:29 -0300 |
commit | 217ece6129f2d3b4fdd18d9e79be9e43d8d14a42 (patch) | |
tree | b2bbd81042f48e862e0c0b8743edc932102640bb /virt/kvm/kvm_main.c | |
parent | 34bb10b79de7df118de832f6832efb630e646577 (diff) | |
download | linux-stable-217ece6129f2d3b4fdd18d9e79be9e43d8d14a42.tar.gz linux-stable-217ece6129f2d3b4fdd18d9e79be9e43d8d14a42.tar.bz2 linux-stable-217ece6129f2d3b4fdd18d9e79be9e43d8d14a42.zip |
KVM: use yield_to instead of sleep in kvm_vcpu_on_spin
Instead of sleeping in kvm_vcpu_on_spin, which can cause gigantic
slowdowns of certain workloads, we instead use yield_to to get
another VCPU in the same KVM guest to run sooner.
This seems to give a 10-15% speedup in certain workloads.
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'virt/kvm/kvm_main.c')
-rw-r--r-- | virt/kvm/kvm_main.c | 57 |
1 files changed, 47 insertions, 10 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index bc8bfd15ab71..2dc53a6dc285 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1484,18 +1484,55 @@ void kvm_resched(struct kvm_vcpu *vcpu) } EXPORT_SYMBOL_GPL(kvm_resched); -void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu) +void kvm_vcpu_on_spin(struct kvm_vcpu *me) { - ktime_t expires; - DEFINE_WAIT(wait); - - prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); - - /* Sleep for 100 us, and hope lock-holder got scheduled */ - expires = ktime_add_ns(ktime_get(), 100000UL); - schedule_hrtimeout(&expires, HRTIMER_MODE_ABS); + struct kvm *kvm = me->kvm; + struct kvm_vcpu *vcpu; + int last_boosted_vcpu = me->kvm->last_boosted_vcpu; + int yielded = 0; + int pass; + int i; - finish_wait(&vcpu->wq, &wait); + /* + * We boost the priority of a VCPU that is runnable but not + * currently running, because it got preempted by something + * else and called schedule in __vcpu_run. Hopefully that + * VCPU is holding the lock that we need and will release it. + * We approximate round-robin by starting at the last boosted VCPU. + */ + for (pass = 0; pass < 2 && !yielded; pass++) { + kvm_for_each_vcpu(i, vcpu, kvm) { + struct task_struct *task = NULL; + struct pid *pid; + if (!pass && i < last_boosted_vcpu) { + i = last_boosted_vcpu; + continue; + } else if (pass && i > last_boosted_vcpu) + break; + if (vcpu == me) + continue; + if (waitqueue_active(&vcpu->wq)) + continue; + rcu_read_lock(); + pid = rcu_dereference(vcpu->pid); + if (pid) + task = get_pid_task(vcpu->pid, PIDTYPE_PID); + rcu_read_unlock(); + if (!task) + continue; + if (task->flags & PF_VCPU) { + put_task_struct(task); + continue; + } + if (yield_to(task, 1)) { + put_task_struct(task); + kvm->last_boosted_vcpu = i; + yielded = 1; + break; + } + put_task_struct(task); + } + } } EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin); |