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SubjectRe: [PATCH] sched: account system time properly
Martin Schwidefsky a écrit :
> On Wed, 29 Apr 2009 09:46:17 +0200
> Eric Dumazet <dada1@cosmosbay.com> wrote:
>
>> Eric Dumazet a écrit :
>>> Andrew Morton a écrit :
>>>
>>> So, if IRQs are interrupting idle task, I guess if (p != rq->idle) will be false.
>>>
>
> If an IRQ interrupts the idle task the tick is supposed to be accounted
> as an idle tick. Only if the IRQ interrupted the system while it has
> been in hardirq or softirq processing then it should be accounted as
> system tick.
>
>> Maybe following patch is needed ?
>>
>> [PATCH] sched: account system time properly
>>
>> When idle task is interrupted by an IRQ, time accounting considers CPU is idle,
>> even while it should account for hard or softirq.
>>
>> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
>>
>> diff --git a/kernel/sched.c b/kernel/sched.c
>> index b902e58..26efa47 100644
>> --- a/kernel/sched.c
>> +++ b/kernel/sched.c
>> @@ -4732,7 +4732,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
>>
>> if (user_tick)
>> account_user_time(p, one_jiffy, one_jiffy_scaled);
>> - else if (p != rq->idle)
>> + else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))
>> account_system_time(p, HARDIRQ_OFFSET, one_jiffy,
>> one_jiffy_scaled);
>> else
>
> That patch makes a lot of sense to me. Does it fix the problem?
>

Yes it does, on my machine at least :

11:18:48 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %idle
11:18:58 AM all 0.00 0.00 0.00 0.00 0.21 0.69 0.00 0.00 99.10
11:18:58 AM 0 0.00 0.00 0.00 0.00 1.70 5.50 0.00 0.00 92.80 << HERE >>
11:18:58 AM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
11:18:58 AM 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00



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