From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758027Ab2GLTUq (ORCPT ); Thu, 12 Jul 2012 15:20:46 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:51477 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757888Ab2GLTUn (ORCPT ); Thu, 12 Jul 2012 15:20:43 -0400 From: Raghavendra K T To: "H. Peter Anvin" , Thomas Gleixner , Avi Kivity , Ingo Molnar , Marcelo Tosatti , Rik van Riel Cc: S390 , Carsten Otte , Christian Borntraeger , KVM , Raghavendra K T , chegu vinod , "Andrew M. Theurer" , LKML , X86 , Gleb Natapov , linux390@de.ibm.com, Srivatsa Vaddagiri , Joerg Roedel Date: Fri, 13 Jul 2012 00:48:24 +0530 Message-Id: <20120712191822.30440.56318.sendpatchset@codeblue> In-Reply-To: <20120712191712.30440.68944.sendpatchset@codeblue> References: <20120712191712.30440.68944.sendpatchset@codeblue> Subject: [PATCH RFC V3 3/3] kvm: Choose better candidate for directed yield x-cbid: 12071209-7014-0000-0000-0000018CD8E8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Raghavendra K T Currently, on a large vcpu guests, there is a high probability of yielding to the same vcpu who had recently done a pause-loop exit or cpu relax intercepted. Such a yield can lead to the vcpu spinning again and hence degrade the performance. The patchset keeps track of the pause loop exit/cpu relax interception and gives chance to a vcpu which: (a) Has not done pause loop exit or cpu relax intercepted at all (probably he is preempted lock-holder) (b) Was skipped in last iteration because it did pause loop exit or cpu relax intercepted, and probably has become eligible now (next eligible lock holder) Signed-off-by: Raghavendra K T --- v2 patches were: Reviewed-by: Rik van Riel virt/kvm/kvm_main.c | 34 ++++++++++++++++++++++++++++++++++ 1 files changed, 34 insertions(+), 0 deletions(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4ec0120..50f6e60 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1570,6 +1570,38 @@ bool kvm_vcpu_yield_to(struct kvm_vcpu *target) } EXPORT_SYMBOL_GPL(kvm_vcpu_yield_to); +/* + * Helper that checks whether a VCPU is eligible for directed yield. + * Most eligible candidate to yield is decided by following heuristics: + * + * (a) VCPU which has not done pl-exit or cpu relax intercepted recently + * (preempted lock holder), indicated by @cpu_relax_intercepted. + * Set at the beiginning and cleared at the end of interception/PLE handler. + * + * (b) VCPU which has done pl-exit/ cpu relax intercepted but did not get + * chance last time (mostly it has become eligible now since we have probably + * yielded to lockholder in last iteration. This is done by toggling + * @dy_eligible each time a VCPU checked for eligibility.) + * + * Yielding to a recently pl-exited/cpu relax intercepted VCPU before yielding + * to preempted lock-holder could result in wrong VCPU selection and CPU + * burning. Giving priority for a potential lock-holder increases lock + * progress. + */ +bool kvm_vcpu_check_and_update_eligible(struct kvm_vcpu *vcpu) +{ + bool eligible; + + eligible = !vcpu->ple.cpu_relax_intercepted || + (vcpu->ple.cpu_relax_intercepted && + vcpu->ple.dy_eligible); + + if (vcpu->ple.cpu_relax_intercepted) + vcpu->ple.dy_eligible = !vcpu->ple.dy_eligible; + + return eligible; +} + void kvm_vcpu_on_spin(struct kvm_vcpu *me) { struct kvm *kvm = me->kvm; @@ -1598,6 +1630,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (waitqueue_active(&vcpu->wq)) continue; + if (!kvm_vcpu_check_and_update_eligible(vcpu)) + continue; if (kvm_vcpu_yield_to(vcpu)) { kvm->last_boosted_vcpu = i; yielded = 1;