2016-06-07 18:47 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>
>
> On 07/06/2016 10:00, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> This patch adds guest steal-time support to full dynticks CPU
>> time accounting. After the following commit:
>>
>> ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")
>>
>> ... time sampling became jiffy based, even if it's still listened
>> to ring boundaries, so steal_account_process_tick() is reused
>> to account how many 'ticks' are stolen-time, after the last accumulation.
>
> I still have no idea how to parse this. What are "ring boundaries"?
> Rik, can you suggest a better commit message?
It is original from this slides.
http://ertl.jp/~shinpei/conf/ospert13/slides/FredericWeisbecker.pdf,
slide 28.
>
>> Suggested-and-Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
>
> Please split Suggested-by and Reviewed-by.
>
>> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
>> index 75f98c5..9ff036b 100644
>> --- a/kernel/sched/cputime.c
>> +++ b/kernel/sched/cputime.c
>> @@ -257,7 +257,7 @@ void account_idle_time(cputime_t cputime)
>> cpustat[CPUTIME_IDLE] += (__force u64) cputime;
>> }
>>
>> -static __always_inline bool steal_account_process_tick(void)
>> +static __always_inline unsigned long steal_account_process_tick(void)
>> {
>> #ifdef CONFIG_PARAVIRT
>> if (static_key_false(¶virt_steal_enabled)) {
>> @@ -279,7 +279,7 @@ static __always_inline bool steal_account_process_tick(void)
>> return steal_jiffies;
>> }
>> #endif
>> - return false;
>> + return 0;
>> }
>>
>> /*
>> @@ -691,9 +691,13 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
>>
>> static void __vtime_account_system(struct task_struct *tsk)
>> {
>> - cputime_t delta_cpu = get_vtime_delta(tsk);
>> + cputime_t delta_time = get_vtime_delta(tsk);
>> + cputime_t steal_time = jiffies_to_cputime(steal_account_process_tick());
>>
>> - account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
>> + if (steal_time < delta_time) {
>> + delta_time -= steal_time;
>> + account_system_time(tsk, irq_count(), delta_time, cputime_to_scaled(delta_time));
>> + }
>> }
>>
>> void vtime_account_system(struct task_struct *tsk)
>> @@ -718,13 +722,18 @@ void vtime_gen_account_irq_exit(struct task_struct *tsk)
>>
>> void vtime_account_user(struct task_struct *tsk)
>> {
>> - cputime_t delta_cpu;
>> + cputime_t delta_time, steal_time;
>>
>> write_seqcount_begin(&tsk->vtime_seqcount);
>> tsk->vtime_snap_whence = VTIME_SYS;
>> if (vtime_delta(tsk)) {
>> - delta_cpu = get_vtime_delta(tsk);
>> - account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
>> + delta_time = get_vtime_delta(tsk);
>> + steal_time = jiffies_to_cputime(steal_account_process_tick());
>> +
>> + if (steal_time < delta_time) {
>> + delta_time -= steal_time;
>> + account_user_time(tsk, delta_time, cputime_to_scaled(delta_time));
>> + }
>> }
>> write_seqcount_end(&tsk->vtime_seqcount);
>> }
>>
>
> You're adding almost the same code to two callers of get_vtime_delta out
> of three. I don't know the vtime accounting code very well, but why
> doesn't the same apply to account_idle_time?
>
> If it does, you should instead change get_vtime_delta to process steal
> time and subtract it from the result.
>
> Secondarily, when can it happen that steal_time > delta_time?
>
> Thanks,
>
> Paolo
--
Regards,
Wanpeng Li
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