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sched/cputime: Fix steal time accounting 

Commit:

  5743021831 ("sched/cputime: Count actually elapsed irq & softirq time")

... didn't take steal time into consideration with passing the noirqtime
kernel parameter.

As Paolo pointed out before:

| Why not? If idle=poll, for example, any time the guest is suspended (and
| thus cannot poll) does count as stolen time.

This patch fixes it by reducing steal time from idle time accounting when
the noirqtime parameter is true. The average idle time drops from 56.8%
to 54.75% for nohz idle kvm guest(noirqtime, idle=poll, four vCPUs running
on one pCPU).

Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Radim <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1470893795-3527-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
hifive-unleashed-5.1
Wanpeng Li 2016-08-11 13:36:35 +08:00 committed by Ingo Molnar
parent c0c8c9fa21
commit f9bcf1e0e0
1 changed files with 9 additions and 2 deletions
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11
kernel/sched/cputime.c
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@ -508,13 +508,20 @@ void account_process_tick(struct task_struct *p, int user_tick)
*/
void account_idle_ticks(unsigned long ticks)
{
cputime_t cputime, steal;
if (sched_clock_irqtime) {
irqtime_account_idle_ticks(ticks);
return;
}
account_idle_time(jiffies_to_cputime(ticks));
cputime = cputime_one_jiffy;
steal = steal_account_process_time(cputime);
if (steal >= cputime)
return;
cputime -= steal;
account_idle_time(cputime);
}
/*