Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761410AbZJIU3z (ORCPT ); Fri, 9 Oct 2009 16:29:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753443AbZJIU3y (ORCPT ); Fri, 9 Oct 2009 16:29:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58058 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752130AbZJIU3x (ORCPT ); Fri, 9 Oct 2009 16:29:53 -0400 Message-ID: <4ACF9C9B.2040006@redhat.com> Date: Fri, 09 Oct 2009 10:27:07 -1000 From: Zachary Amsden User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20090922 Fedora/3.0-2.7.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Jan Kiszka CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Avi Kivity , Marcelo Tosatti Subject: Re: [PATCH v4: kvm 2/4] Kill the confusing tsc_ref_khz and ref_freq variables. References: <4AC1C59F.6010703@redhat.com> <1254260317-3490-1-git-send-email-zamsden@redhat.com> <1254260317-3490-2-git-send-email-zamsden@redhat.com> <4ACE734D.10600@web.de> In-Reply-To: <4ACE734D.10600@web.de> 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: 2989 Lines: 82 On 10/08/2009 01:18 PM, Jan Kiszka wrote: > Zachary Amsden wrote: > >> They are globals, not clearly protected by any ordering or locking, and >> vulnerable to various startup races. >> >> Instead, for variable TSC machines, register the cpufreq notifier and get >> the TSC frequency directly from the cpufreq machinery. Not only is it >> always right, it is also perfectly accurate, as no error prone measurement >> is required. >> >> On such machines, when a new CPU online is brought online, it isn't clear what >> frequency it will start with, and it may not correspond to the reference, thus >> in hardware_enable we clear the cpu_tsc_khz variable to zero and make sure >> it is set before running on a VCPU. >> >> Signed-off-by: Zachary Amsden >> --- >> arch/x86/kvm/x86.c | 26 ++++++++++++++++---------- >> 1 files changed, 16 insertions(+), 10 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 15d2ace..de4ce8f 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1326,6 +1326,8 @@ out: >> void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >> { >> kvm_x86_ops->vcpu_load(vcpu, cpu); >> + if (unlikely(per_cpu(cpu_tsc_khz, cpu) == 0)) >> + per_cpu(cpu_tsc_khz, cpu) = cpufreq_quick_get(cpu); >> kvm_request_guest_time_update(vcpu); >> } >> >> @@ -3061,9 +3063,6 @@ static void bounce_off(void *info) >> /* nothing */ >> } >> >> -static unsigned int ref_freq; >> -static unsigned long tsc_khz_ref; >> - >> static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long val, >> void *data) >> { >> @@ -3072,14 +3071,11 @@ static int kvmclock_cpufreq_notifier(struct notifier_block *nb, unsigned long va >> struct kvm_vcpu *vcpu; >> int i, send_ipi = 0; >> >> - if (!ref_freq) >> - ref_freq = freq->old; >> - >> if (val == CPUFREQ_PRECHANGE&& freq->old> freq->new) >> return 0; >> if (val == CPUFREQ_POSTCHANGE&& freq->old< freq->new) >> return 0; >> - per_cpu(cpu_tsc_khz, freq->cpu) = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new); >> + per_cpu(cpu_tsc_khz, freq->cpu) = freq->new; >> >> spin_lock(&kvm_lock); >> list_for_each_entry(kvm,&vm_list, vm_list) { >> @@ -3120,12 +3116,14 @@ static void kvm_timer_init(void) >> { >> int cpu; >> >> - for_each_possible_cpu(cpu) >> - per_cpu(cpu_tsc_khz, cpu) = tsc_khz; >> if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) { >> - tsc_khz_ref = tsc_khz; >> cpufreq_register_notifier(&kvmclock_cpufreq_notifier_block, >> CPUFREQ_TRANSITION_NOTIFIER); >> + for_each_online_cpu(cpu) >> + per_cpu(cpu_tsc_khz, cpu) = cpufreq_get(cpu); >> > This doesn't build for !CONFIG_CPU_FREQ. > And did it before? -- 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/