From mboxrd@z Thu Jan 1 00:00:00 1970 From: Glauber Costa Subject: Re: [patch 18/18] KVM: x86: update pvclock area conditionally, on cpu migration Date: Tue, 20 Nov 2012 13:01:12 +0400 Message-ID: <50AB46D8.5010400@parallels.com> References: <20121119215758.686768790@redhat.com> <20121119215959.499058001@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: , , , To: Marcelo Tosatti Return-path: Received: from mx2.parallels.com ([64.131.90.16]:60940 "EHLO mx2.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171Ab2KTJBY (ORCPT ); Tue, 20 Nov 2012 04:01:24 -0500 In-Reply-To: <20121119215959.499058001@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 11/20/2012 01:58 AM, Marcelo Tosatti wrote: > As requested by Glauber, do not update kvmclock area on vcpu->pcpu > migration, in case the host has stable TSC. > > This is to reduce cacheline bouncing. > > Signed-off-by: Marcelo Tosatti > > Index: vsyscall/arch/x86/kvm/x86.c > =================================================================== > --- vsyscall.orig/arch/x86/kvm/x86.c > +++ vsyscall/arch/x86/kvm/x86.c > @@ -2615,7 +2615,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu > kvm_x86_ops->write_tsc_offset(vcpu, offset); > vcpu->arch.tsc_catchup = 1; > } > - kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); > + /* > + * On a host with synchronized TSC, there is no need to update > + * kvmclock on vcpu->cpu migration > + */ > + if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) > + kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); > if (vcpu->cpu != cpu) > kvm_migrate_timers(vcpu); > vcpu->cpu = cpu; Ok. Since you are only touching the one in kvm_arch_vcpu_load() and leaving the others untouched, it looks correct. Acked-by: Glauber Costa