Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754488Ab0DNJUh (ORCPT ); Wed, 14 Apr 2010 05:20:37 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36829 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752542Ab0DNJUf (ORCPT ); Wed, 14 Apr 2010 05:20:35 -0400 Message-ID: <4BC588CF.5010507@redhat.com> Date: Wed, 14 Apr 2010 12:20:15 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: "Zhang, Yanmin" CC: Ingo Molnar , Peter Zijlstra , Sheng Yang , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti , oerg Roedel , Jes Sorensen , Gleb Natapov , Zachary Amsden , zhiteng.huang@intel.com, tim.c.chen@intel.com, Arnaldo Carvalho de Melo Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side References: <1902387910.2078.435.camel@ymzhang.sh.intel.com> In-Reply-To: <1902387910.2078.435.camel@ymzhang.sh.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2229 Lines: 68 On 04/14/2030 12:05 PM, Zhang, Yanmin wrote: > Here is the new patch of V3 against tip/master of April 13th > if anyone wants to try it. > > Thanks for persisting despite the flames. Can you please separate arch/x86/kvm part of the patch? That will make for easier reviewing, and will need to go through separate trees. Sheng, did you make any progress with the NMI injection issue? > + > diff -Nraup linux-2.6_tip0413/arch/x86/kvm/x86.c linux-2.6_tip0413_perfkvm/arch/x86/kvm/x86.c > --- linux-2.6_tip0413/arch/x86/kvm/x86.c 2010-04-14 11:11:04.341042024 +0800 > +++ linux-2.6_tip0413_perfkvm/arch/x86/kvm/x86.c 2010-04-14 11:32:45.841278890 +0800 > @@ -3765,6 +3765,35 @@ static void kvm_timer_init(void) > } > } > > +static DEFINE_PER_CPU(struct kvm_vcpu *, current_vcpu); > + > +static int kvm_is_in_guest(void) > +{ > + return percpu_read(current_vcpu) != NULL; > An even more accurate way to determine this is to check whether the interrupt frame points back at the 'int $2' instruction. However we plan to switch to a self-IPI method to inject the NMI, and I'm not sure wether APIC NMIs are accepted on an instruction boundary or whether there's some latency involved. > +static unsigned long kvm_get_guest_ip(void) > +{ > + unsigned long ip = 0; > + if (percpu_read(current_vcpu)) > + ip = kvm_rip_read(percpu_read(current_vcpu)); > + return ip; > +} > This may be racy. kvm_rip_read() accesses a cache in memory; if we're in the process of updating the cache, then we may read a stale value. See below. > > trace_kvm_entry(vcpu->vcpu_id); > + > + percpu_write(current_vcpu, vcpu); > kvm_x86_ops->run(vcpu); > + percpu_write(current_vcpu, NULL); > If you move this around the 'int $2' instructions you will close the race, as a stray NMI won't catch us updating the rip cache. But that depends on whether self-IPI is accepted on the next instruction or not. -- error compiling committee.c: too many arguments to function -- 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/