Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755053Ab2KZMNP (ORCPT ); Mon, 26 Nov 2012 07:13:15 -0500 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:55787 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754924Ab2KZMNL (ORCPT ); Mon, 26 Nov 2012 07:13:11 -0500 From: Raghavendra K T To: Peter Zijlstra , "H. Peter Anvin" , Avi Kivity , Gleb Natapov , Ingo Molnar , Marcelo Tosatti , Rik van Riel Cc: Srikar , "Nikunj A. Dadhania" , KVM , Raghavendra K T , Jiannan Ouyang , Chegu Vinod , "Andrew M. Theurer" , LKML , Srivatsa Vaddagiri , Andrew Jones Date: Mon, 26 Nov 2012 17:38:04 +0530 Message-Id: <20121126120804.2595.20280.sendpatchset@codeblue> In-Reply-To: <20121126120740.2595.33651.sendpatchset@codeblue> References: <20121126120740.2595.33651.sendpatchset@codeblue> Subject: [PATCH V3 RFC 2/2] kvm: Handle yield_to failure return code for potential undercommit case x-cbid: 12112612-0260-0000-0000-000002369D3D Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3006 Lines: 102 From: Raghavendra K T yield_to returns -ESRCH, When source and target of yield_to run queue length is one. When we see three 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..053f494 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 = 3; 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; } } } -- 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/