Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757949Ab0LBTpl (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 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 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2959 Lines: 102 Instead of sleeping in kvm_vcpu_on_spin, which can cause gigantic slowdowns of certain workloads, we instead use yield_to to hand the rest of our timeslice to another vcpu in the same KVM guest. Signed-off-by: Rik van Riel Signed-off-by: Marcelo Tosatti 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); -- All rights reversed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/