HZ = 1000 slows down application

[Luigi Rizzo]

On Mon, Sep 22, 2003 at 02:43:40PM -0400, akanwar at digitarchy.com wrote:
...
> But now I noticed that my application is occassionally doing slower
> iterations. Average iteration time used to be 0.2 ms without polling
> enabled. With the device polling changes, the average time is still around
> the same, but once every few minutes the application sees iterations that
> are 3.3 seconds (*seconds*, not a typo) long. 

most likely your application makes some assumptions on the duration of
a clock tick and then it gets confused when, say, a select returns
quicker, or some time difference becomes negative, etc. etc. because
of the finer granularity.

very common type of bug.

	cheers
	luigi

> This seems to happen as soon as I use the kernel with HZ=1000. Enabling or
> disabling device polling does not seem to make any difference to this
> behavior. I am trying to understand why there seem to be a few really long
> iterations. Could it happen that the application does not get any CPU for
> that long? Seems very counter intuitive that higher HZ should cause this. 
> 
> Could anyone shed any light on what is happening ?
> 
> Thanks,
> -ansh
> 
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