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SubjectRe: [PATCH] sched: account system time properly

* Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> On Wed, 29 Apr 2009 11:20:03 +0200
> Eric Dumazet <dada1@cosmosbay.com> wrote:
>
> > 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
>
> Very good. Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

Thanks.

Eric, mind (re-)sending the patch with Martin's ack included, and
with either a suitable impact-line footer or an extra paragraph that
describes the bug you found (and how it shows up in practice) and
how the patch fixed that problem.

Thanks,

Ingo
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