From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: [PATCH v4: kvm 2/4] Kill the confusing tsc_ref_khz and ref_freq variables. Date: Fri, 09 Oct 2009 10:36:47 -1000 Message-ID: <4ACF9EDF.5000808@redhat.com> 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> <4ACF9C9B.2040006@redhat.com> <4ACF9EC3.2050901@web.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Avi Kivity , Marcelo Tosatti To: Jan Kiszka Return-path: In-Reply-To: <4ACF9EC3.2050901@web.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 10/09/2009 10:36 AM, Jan Kiszka wrote: > Zachary Amsden wrote: > >> 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? >> > Yes, because cpufreq_get, which is undefined without CONFIG_CPU_FREQ, > did not exist so far. One may argue that this is a deficit of the > cpufreq API. However, it needs fixing. > I'll send a patch today. I'm going with API deficient and will fix that, but this means I will also require a fix for kvm-kmod :( Zach