From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751720Ab2KIIn1 (ORCPT ); Fri, 9 Nov 2012 03:43:27 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:56765 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751629Ab2KIInX (ORCPT ); Fri, 9 Nov 2012 03:43:23 -0500 Date: Fri, 9 Nov 2012 14:08:37 +0530 From: Raghavendra K T To: Avi Kivity Cc: Peter Zijlstra , "H. Peter Anvin" , Marcelo Tosatti , Ingo Molnar , Rik van Riel , Srikar , "Nikunj A. Dadhania" , KVM , Jiannan Ouyang , Chegu Vinod , "Andrew M. Theurer" , LKML , Srivatsa Vaddagiri , Gleb Natapov , Andrew Jones Subject: Re: [PATCH V2 RESEND RFC 2/3] kvm: Handle yield_to failure return code for potential undercommit case Message-ID: <20121109083837.GA1398@linux.vnet.ibm.com> Reply-To: Raghavendra K T References: <20121029140621.15448.92083.sendpatchset@codeblue> <20121029140702.15448.56932.sendpatchset@codeblue> <50911BC3.6080305@redhat.com> <50911C7D.5080307@linux.vnet.ibm.com> <50912463.3040201@linux.vnet.ibm.com> <50912A72.6050307@redhat.com> <50915A91.1040001@linux.vnet.ibm.com> <20121107102545.GA18644@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20121107102545.GA18644@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12110908-4834-0000-0000-00000044B72F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Handle yield_to failure return code for potential undercommit case From: Raghavendra K T yield_to returns -ESRCH when When source and target of yield_to run queue length is one. When we see two successive failures of yield_to we assume we are in potential undercommit case and abort from PLE handler. The assumption is backed by low probability of wrong decision for even worst case scenarios such as average runqueue length between 1 and 2. note that we do not update last boosted vcpu in failure cases. Thank Avi for raising question on aborting after first fail from yield_to. Reviewed-by: Srikar Dronamraju Signed-off-by: Raghavendra K T --- virt/kvm/kvm_main.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index be70035..9f390e7 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1639,6 +1639,7 @@ bool kvm_vcpu_yield_to(struct kvm_vcpu *target) { struct pid *pid; struct task_struct *task = NULL; + bool ret = false; rcu_read_lock(); pid = rcu_dereference(target->pid); @@ -1646,17 +1647,15 @@ bool kvm_vcpu_yield_to(struct kvm_vcpu *target) task = get_pid_task(target->pid, PIDTYPE_PID); rcu_read_unlock(); if (!task) - return false; + return ret; if (task->flags & PF_VCPU) { put_task_struct(task); - return false; - } - if (yield_to(task, 1)) { - put_task_struct(task); - return true; + return ret; } + ret = yield_to(task, 1); put_task_struct(task); - return false; + + return ret; } EXPORT_SYMBOL_GPL(kvm_vcpu_yield_to); @@ -1697,12 +1696,14 @@ bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu) return eligible; } #endif + void kvm_vcpu_on_spin(struct kvm_vcpu *me) { struct kvm *kvm = me->kvm; struct kvm_vcpu *vcpu; int last_boosted_vcpu = me->kvm->last_boosted_vcpu; int yielded = 0; + int try = 2; int pass; int i; @@ -1714,7 +1715,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) * 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++) { + for (pass = 0; pass < 2 && !yielded && try; pass++) { kvm_for_each_vcpu(i, vcpu, kvm) { if (!pass && i <= last_boosted_vcpu) { i = last_boosted_vcpu; @@ -1727,10 +1728,15 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) continue; - if (kvm_vcpu_yield_to(vcpu)) { + + yielded = kvm_vcpu_yield_to(vcpu); + if (yielded > 0) { kvm->last_boosted_vcpu = i; - yielded = 1; break; + } else if (yielded < 0) { + try--; + if (!try) + break; } } }