linux-kernel - Re: [PATCH v2] sched/cputime: add steal time support to full dynticks CPU time accounting

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Date:	Wed, 18 May 2016 18:06:00 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Mika Penttilä <mika.penttila@...tfour.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paolo Bonzini <pbonzini@...hat.com>, Radim <rkrcmar@...hat.com>
Subject: Re: [PATCH v2] sched/cputime: add steal time support to full dynticks
 CPU time accounting

2016-05-18 17:46 GMT+08:00 Mika Penttilä <mika.penttila@...tfour.com>:
> On 05/18/2016 11:28 AM, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> This patch adds steal guest time support to full dynticks CPU
>> time accounting. After 'commit ff9a9b4c4334 ("sched, time: Switch
>> VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")', time is jiffy
>> based sampling even if it's still listened to ring boundaries, so
>> steal_account_process_tick() is reused to account how much 'ticks'
>> are steal time after the last accumulation.
>>
>> Suggested-by: Rik van Riel <riel@...hat.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
>> Cc: Rik van Riel <riel@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>> v1 -> v2:
>>  * fix divide zero bug, thanks Rik
>>
>>  kernel/sched/cputime.c | 13 +++++++++++--
>>  1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
>> index 75f98c5..bfa50a0 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(&paravirt_steal_enabled)) {
>> @@ -279,7 +279,7 @@ static __always_inline bool steal_account_process_tick(void)
>>               return steal_jiffies;
>>       }
>>  #endif
>> -     return false;
>> +     return 0;
>>  }
>>
>>  /*
>> @@ -691,8 +691,12 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
>>
>>  static void __vtime_account_system(struct task_struct *tsk)
>>  {
>> +     unsigned long steal_time = steal_account_process_tick();
>>       cputime_t delta_cpu = get_vtime_delta(tsk);
>>
>> +     if (steal_time >= delta_cpu)
>> +             return;
>> +     delta_cpu -= steal_time;
>>       account_system_time(tsk, irq_count(), delta_cpu, cputime_to_scaled(delta_cpu));
>>  }
>>
>> @@ -723,7 +727,12 @@ void vtime_account_user(struct task_struct *tsk)
>>       write_seqcount_begin(&tsk->vtime_seqcount);
>>       tsk->vtime_snap_whence = VTIME_SYS;
>>       if (vtime_delta(tsk)) {
>> +             unsigned long steal_time = steal_account_process_tick();
>>               delta_cpu = get_vtime_delta(tsk);
>
>
> afaik steal_account_process_tick() returns jiffies and get_vtime_delta() cputime, so can't mix them like this : ?

You are right, thanks for your review. I will fix it.

Regards,
Wanpeng Li