From da4ad88cab5867ee240dfd0585e9d115a8cc47db Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Thu, 23 Apr 2020 22:48:37 -0700 Subject: 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 Cc: kvmarm@lists.cs.columbia.edu Cc: linux-mips@vger.kernel.org Reviewed-by: Marc Zyngier Signed-off-by: Davidlohr Bueso Message-Id: <20200424054837.5138-6-dave@stgolabs.net> [Avoid extra logic changes. - Paolo] Signed-off-by: Paolo Bonzini --- virt/kvm/async_pf.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'virt/kvm/async_pf.c') 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); -- cgit v1.2.3