Re: [PATCH, RFC] use hrtimer in sched_clock

["Uwe Kleine-König" <Uwe.Kleine-Koenig@digi.com>]

Hello Thomas,

Thomas Gleixner wrote:
> On Fri, 11 Jul 2008, Uwe Kleine-König wrote:
> > This should make it unnecessary to overwrite sched_clock for a higher
> > precision.
> > With this patch I get sub-jiffie timing with CONFIG_PRINTK_TIME=y.
> >
> > Signed-off-by: Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@elte.hu>
> > ---
> > Hello,
> >
> > I tested the patch on arch-arm/mach-ns9xxx and it seem seams to work.
> > But I admit I didn't test it deeply and I didn't measure if there is any
> > overhead.
> 
> There is lots of overhead and your approach is simply wrong.
I expected to have some overhead, but can you please elaborate on
"simply wrong"?
I will try to measure the actual overhead but cannot promise to find
time for that in the near future.
 
> >  unsigned long long __attribute__((weak)) sched_clock(void)
> 
> The correct way to solve it is to override sched_clock() with a high
> resolution implementation for your hardware platform. sched_clock is a
> weak function to provide a default implementation based on jiffies.
> 
> If you do a grep -r sched_clock arch/arm you'll find a couple of
> examples how to override sched_clock().
I new that and my purpose was to make this unneeded.  Would be nice,
wouldn't it?

Thanks and best regards,
Uwe

-- 
Uwe Kleine-König, Software Engineer
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