From patchwork Thu Dec 2 19:45:16 2010 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rik van Riel X-Patchwork-Id: 375721 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by demeter1.kernel.org (8.14.4/8.14.3) with ESMTP id oB2Jkkeg028644 for ; Thu, 2 Dec 2010 19:46:46 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757909Ab0LBTpl (ORCPT ); Thu, 2 Dec 2010 14:45:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:43641 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757877Ab0LBTpk (ORCPT ); Thu, 2 Dec 2010 14:45:40 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id oB2JjVhd001188 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Thu, 2 Dec 2010 14:45:32 -0500 Received: from annuminas.surriel.com (ovpn-113-70.phx2.redhat.com [10.3.113.70]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id oB2JjN7w027291; Thu, 2 Dec 2010 14:45:29 -0500 Date: Thu, 2 Dec 2010 14:45:16 -0500 From: Rik van Riel To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Avi Kiviti , Srivatsa Vaddagiri , Peter Zijlstra , Ingo Molnar , Anthony Liguori Subject: [RFC PATCH 3/3] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin Message-ID: <20101202144516.45a0385d@annuminas.surriel.com> In-Reply-To: <20101202144129.4357fe00@annuminas.surriel.com> References: <20101202144129.4357fe00@annuminas.surriel.com> Organization: Red Hat, Inc. Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.3 (demeter1.kernel.org [140.211.167.41]); Thu, 02 Dec 2010 19:46:46 +0000 (UTC) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index c011ba3..7637dd3 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -90,6 +90,7 @@ struct kvm_vcpu { int fpu_active; int guest_fpu_loaded; wait_queue_head_t wq; + int spinning; int sigset_active; sigset_t sigset; struct kvm_vcpu_stat stat; @@ -185,6 +186,7 @@ struct kvm { #endif struct kvm_vcpu *vcpus[KVM_MAX_VCPUS]; atomic_t online_vcpus; + int last_boosted_vcpu; struct list_head vm_list; struct mutex lock; struct kvm_io_bus *buses[KVM_NR_BUSES]; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 80f17db..a6eeafc 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1880,18 +1880,53 @@ 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); + struct kvm *kvm = me->kvm; + struct kvm_vcpu *vcpu; + int last_boosted_vcpu = me->kvm->last_boosted_vcpu; + int first_round = 1; + int i; - prepare_to_wait(&vcpu->wq, &wait, TASK_INTERRUPTIBLE); + me->spinning = 1; + + /* + * 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. + */ + again: + kvm_for_each_vcpu(i, vcpu, kvm) { + struct task_struct *task = vcpu->task; + if (first_round && i < last_boosted_vcpu) { + i = last_boosted_vcpu; + continue; + } else if (!first_round && i > last_boosted_vcpu) + break; + if (vcpu == me) + continue; + if (vcpu->spinning) + continue; + if (!task) + continue; + if (waitqueue_active(&vcpu->wq)) + continue; + if (task->flags & PF_VCPU) + continue; + kvm->last_boosted_vcpu = i; + yield_to(task); + break; + } - /* Sleep for 100 us, and hope lock-holder got scheduled */ - expires = ktime_add_ns(ktime_get(), 100000UL); - schedule_hrtimeout(&expires, HRTIMER_MODE_ABS); + if (first_round && last_boosted_vcpu == kvm->last_boosted_vcpu) { + /* We have not found anyone yet. */ + first_round = 0; + goto again; + } - finish_wait(&vcpu->wq, &wait); + me->spinning = 0; } EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin);