On Mon, 26 Nov 2007 20:36:32 -0600 (CST) [email protected] wrote:
> Question: Why is ksoftirqd eating about 5 to 10 percent of my CPU on an idle
> system? The problem occurs if I config the kernel with tickless
> support (i.e. CONFIG_TICK_ONESHOT=y). (Thanks to "oprofile" for putting me
> onto this.)
beware that oprofile can provide misleading results on a paritally-idle
system. You may have discovered that ksoftirqd is consuming 5-10% of the
non-idle time on that idle system, which is less surprising.
> I have noted this same problem on kernel versions: 2.6.23.1, 2.6.23.8 and
> 2.6.23.9
>
> **************************************************************************
> *** Output from "vmstat -n 1 10" -- Note very high context switch rate ***
> *** This is on a idle machine! ***
> **************************************************************************
>
> procs -----------memory---------- ---swap-- -----io---- --system--
> ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy
> id wa
> 0 0 0 1925556 4768 116104 0 0 124 2 6 7538 1 2
> 96 1
> 0 0 0 1925556 4768 116104 0 0 0 0 2 147329 0 1
> 99 0
> 0 0 0 1925548 4768 116104 0 0 0 0 0 154515 0 1
> 99 0
> 0 0 0 1925548 4768 116104 0 0 0 0 1 153898 0 2
> 98 0
> 0 0 0 1925548 4780 116104 0 0 0 16 3 155216 0 1
> 99 0
> 0 0 0 1925548 4780 116104 0 0 0 0 1 161718 0 1
> 99 0
> 0 0 0 1925548 4780 116104 0 0 0 0 0 147587 0 2
> 98 0
> 0 0 0 1925548 4780 116104 0 0 0 0 1 153524 0 2
> 98 0
> 0 0 0 1925448 4780 116104 0 0 0 0 0 153434 0 1
> 99 0
> 0 0 0 1925448 4792 116092 0 0 0 16 4 153527 0 2
> 98 0
So what piece of code is scheduling so much? What does `top' say? What
does the (sorted) output of oprofile look like?
Did you try shutting down as much userspace code as possible to find out if
some userspace task is misbehaving?
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