Hello,
Thomas Gleixner wrote:
> On Tue, 2007-06-26 at 17:00 +0200, Uwe Kleine-K??nig wrote:
> > If I enable NO_HZ, the system jerks (I hope this is an understandable
> > term ...). E.g.
> >
> > # time find /sys
> > ...
> > real 1m 19.52s
> > user 0m 0.18s
> > sys 0m 0.15s
> >
> > on a freshly booted machine. The output comes in several hunks with
> > pausing between them. With no_hz=off, I get approx. the same.
>
> it's nohz=off not no_hz=off
Currently I'm not sure, which I was really using. I think it was the
right one, because dmesg changed. But anyhow, I will retest if I made
it wrong.
> > First I wondered why set_next_event is called twice between two timer
> > interrupts most of the time. I found out that the timer is programed
> > for the next tick in any case and if nothing needs the next tick, the
> > interval is enlarged. I didn't spend time yet to check if it is
> > easier/faster to only program the timer once.
>
> We optimize for the non-idle path, i.e. we keep the timer running as
> long as we are not idle. Once we go idle we reprogram it.
OK, sounds sane.
> I looked at the patch and as far as I can understand it, there is
> nothing obviously wrong about it.
What a pity.
> One remark: why did you expand the clocksource to be 64 bit? The generic
> code handles the 32 bit wrap already, so the expansion in your read
> routine is adding overhead. The counter will wrap every 24 seconds, so
> there is nothing to worry about.
OK, I thought it to be better to have 64bit + some overhead. I will
change that.
> The behavior you are describing is might be related to some problem with
> the clocksource readout, as the reprogramming values are calculated from
> there.
Any hints how I can debug that?
Currently I cannot retest, but I will dig into it again and rereport.
Thanks for your answer.
Best regards
Uwe
--
Uwe Kleine-Koenig
http://www.google.com/search?q=speed+of+light%3D
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