From patchwork Wed Jul 18 13:38:00 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Raghavendra K T X-Patchwork-Id: 1211031 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-process-083081@patchwork2.kernel.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by patchwork2.kernel.org (Postfix) with ESMTP id E72FBDFFFD for ; Wed, 18 Jul 2012 13:40:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754489Ab2GRNkP (ORCPT ); Wed, 18 Jul 2012 09:40:15 -0400 Received: from e23smtp06.au.ibm.com ([202.81.31.148]:50200 "EHLO e23smtp06.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752008Ab2GRNkN (ORCPT ); Wed, 18 Jul 2012 09:40:13 -0400 Received: from /spool/local by e23smtp06.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 18 Jul 2012 13:33:19 +1000 Received: from d23relay04.au.ibm.com (202.81.31.246) by e23smtp06.au.ibm.com (202.81.31.212) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; Wed, 18 Jul 2012 13:33:17 +1000 Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q6IDW8VJ30081222; Wed, 18 Jul 2012 23:32:08 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q6IDe7ZH009619; Wed, 18 Jul 2012 23:40:08 +1000 Received: from codeblue.in.ibm.com (codeblue.in.ibm.com [9.124.158.92]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id q6IDe3u8009578; Wed, 18 Jul 2012 23:40:03 +1000 From: Raghavendra K T To: "H. Peter Anvin" , Thomas Gleixner , Avi Kivity , Ingo Molnar , Marcelo Tosatti , Rik van Riel Cc: Srikar , 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: Wed, 18 Jul 2012 19:08:00 +0530 Message-Id: <20120718133800.5321.51446.sendpatchset@codeblue.in.ibm.com> In-Reply-To: <20120718133717.5321.71347.sendpatchset@codeblue.in.ibm.com> References: <20120718133717.5321.71347.sendpatchset@codeblue.in.ibm.com> Subject: [PATCH RFC V5 3/3] kvm: Choose better candidate for directed yield x-cbid: 12071803-7014-0000-0000-000001936931 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@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 was: Reviewed-by: Rik van Riel include/linux/kvm_host.h | 5 +++++ virt/kvm/kvm_main.c | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 41 insertions(+), 0 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 34ce296..952427d 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -923,6 +923,11 @@ static inline void kvm_vcpu_set_dy_eligible(struct kvm_vcpu *vcpu, bool val) { } +static inline bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu) +{ + return true; +} + #endif /* CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT */ #endif diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 3d6ffc8..bf9fb97 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1571,6 +1571,39 @@ bool kvm_vcpu_yield_to(struct kvm_vcpu *target) } EXPORT_SYMBOL_GPL(kvm_vcpu_yield_to); +#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT +/* + * 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 @in_spin_loop. + * 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_eligible_for_directed_yield(struct kvm_vcpu *vcpu) +{ + bool eligible; + + eligible = !vcpu->spin_loop.in_spin_loop || + (vcpu->spin_loop.in_spin_loop && + vcpu->spin_loop.dy_eligible); + + if (vcpu->spin_loop.in_spin_loop) + vcpu->spin_loop.dy_eligible = !vcpu->spin_loop.dy_eligible; + + return eligible; +} +#endif void kvm_vcpu_on_spin(struct kvm_vcpu *me) { struct kvm *kvm = me->kvm; @@ -1599,6 +1632,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) continue; if (waitqueue_active(&vcpu->wq)) continue; + if (!kvm_vcpu_eligible_for_directed_yield(vcpu)) + continue; if (kvm_vcpu_yield_to(vcpu)) { kvm->last_boosted_vcpu = i; yielded = 1; @@ -1607,6 +1642,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me) } } kvm_vcpu_set_in_spin_loop(me, false); + kvm_vcpu_set_dy_eligible(me, false); } EXPORT_SYMBOL_GPL(kvm_vcpu_on_spin);