Zachary Amsden wrote:
> 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<zamsden@xxxxxxxxxx>
>>>>> ---
>>>>> 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 :(
That won't be tricky, I will queue up a fix.
BTW, is the KVM prepared for cpufreq_get returning 0?
Jan
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