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authorDavidlohr Bueso <dave@stgolabs.net>2020-04-23 22:48:37 -0700
committerPaolo Bonzini <pbonzini@redhat.com>2020-05-13 12:14:56 -0400
commitda4ad88cab5867ee240dfd0585e9d115a8cc47db (patch)
treeb145ec0dedb065d2633ba62466cc5c7232a894af /virt/kvm/async_pf.c
parent191a43be61d6791fd4a9098a35c1a09e73f55228 (diff)
kvm: Replace vcpu->swait with rcuwait
The use of any sort of waitqueue (simple or regular) for wait/waking vcpus has always been an overkill and semantically wrong. Because this is per-vcpu (which is blocked) there is only ever a single waiting vcpu, thus no need for any sort of queue. As such, make use of the rcuwait primitive, with the following considerations: - rcuwait already provides the proper barriers that serialize concurrent waiter and waker. - Task wakeup is done in rcu read critical region, with a stable task pointer. - Because there is no concurrency among waiters, we need not worry about rcuwait_wait_event() calls corrupting the wait->task. As a consequence, this saves the locking done in swait when modifying the queue. This also applies to per-vcore wait for powerpc kvm-hv. The x86 tscdeadline_latency test mentioned in 8577370fb0cb ("KVM: Use simple waitqueue for vcpu->wq") shows that, on avg, latency is reduced by around 15-20% with this change. Cc: Paul Mackerras <paulus@ozlabs.org> Cc: kvmarm@lists.cs.columbia.edu Cc: linux-mips@vger.kernel.org Reviewed-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Message-Id: <20200424054837.5138-6-dave@stgolabs.net> [Avoid extra logic changes. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'virt/kvm/async_pf.c')
-rw-r--r--virt/kvm/async_pf.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 15e5b037f92d..10b533f641a6 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -80,8 +80,7 @@ static void async_pf_execute(struct work_struct *work)
trace_kvm_async_pf_completed(addr, cr2_or_gpa);
- if (swq_has_sleeper(&vcpu->wq))
- swake_up_one(&vcpu->wq);
+ rcuwait_wake_up(&vcpu->wait);
mmput(mm);
kvm_put_kvm(vcpu->kvm);