From patchwork Wed Jan 26 22:25:02 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Rik van Riel X-Patchwork-Id: 509841 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 p0QMh6Ko007433 for ; Wed, 26 Jan 2011 22:43:19 GMT Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754244Ab1AZWZo (ORCPT ); Wed, 26 Jan 2011 17:25:44 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33805 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754223Ab1AZWZl (ORCPT ); Wed, 26 Jan 2011 17:25:41 -0500 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id p0QMPXuh001342 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Wed, 26 Jan 2011 17:25:33 -0500 Received: from annuminas.surriel.com (ovpn-113-70.phx2.redhat.com [10.3.113.70]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id p0QMPDlr007297; Wed, 26 Jan 2011 17:25:32 -0500 Date: Wed, 26 Jan 2011 17:25:02 -0500 From: Rik van Riel To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Avi Kiviti , Srivatsa Vaddagiri , Peter Zijlstra , Mike Galbraith , Chris Wright , ttracy@redhat.com, "Nakajima, Jun" Subject: [RFC -v7 PATCH 7/7] kvm: use yield_to instead of sleep in kvm_vcpu_on_spin Message-ID: <20110126172502.63462b77@annuminas.surriel.com> In-Reply-To: <20110126165657.2ddd2ac9@annuminas.surriel.com> References: <20110126165657.2ddd2ac9@annuminas.surriel.com> Organization: Red Hat, Inc. Mime-Version: 1.0 X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 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-4.2.6 (demeter1.kernel.org [140.211.167.41]); Wed, 26 Jan 2011 22:43:19 +0000 (UTC) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 9d56ed5..fab2250 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -187,6 +187,7 @@ 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 86c4905..8b761ba 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1292,18 +1292,55 @@ 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);