Re: Dynticks Causing High Context Switch Rate in ksoftirqd

[Robert Hancock]

bdupree@xxxxxxxxxxxxxxx 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.)
>
> 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

What did oprofile show? It should be able to narrow down what 
function(s) are responsible for the CPU usage..

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@xxxxxxxxxxxxx
Home Page: http://www.roberthancock.com/

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