Commit f5f293a4 authored Apr 29, 2009 by Eric Dumazet Committed by Ingo Molnar Apr 29, 2009

sched: account system time properly



Andrew Gallatin reported that IRQ and SOFTIRQ times were
sometime not reported correctly on recent kernels, and even
bisected to commit 457533a7
([PATCH] fix scaled & unscaled cputime accounting) as the first
bad commit.

Further analysis pointed that commit
79741dd3 ([PATCH] idle cputime
accounting) was the real cause of the problem.

account_process_tick() was not taking into account timer IRQ
interrupting the idle task servicing a hard or soft irq.

On mostly idle cpu, irqs were thus not accounted and top or
mpstat could tell user/admin that cpu was 100 % idle, 0.00 %
irq, 0.00 % softirq, while it was not.

[ Impact: fix occasionally incorrect CPU statistics in top/mpstat ]

Reported-by: Andrew Gallatin <gallatin@myri.com>
Re-reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: rick.jones2@hp.com
Cc: brice@myri.com
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
LKML-Reference: <49F84BC1.7080602@cosmosbay.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 56a50add

kernel/sched.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -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