On Jan 28, 2008 2:46 PM, Jan Kiszka <[EMAIL PROTECTED]> wrote:
> Gilles Chanteperdrix wrote:
> > On Jan 28, 2008 2:34 PM, Jan Kiszka <[EMAIL PROTECTED]> wrote:
> >> Gilles Chanteperdrix wrote:
> >>> ...
> >>> The behaviour you get may be due, for instance, to the fact that the
> >>> processor goes into some sleep mode when idle and to a wake-up
> >>> latency; if you run some load, there is no wake-up latency. It is hard
> >>> to say anything. In order to investigate, I would instrument the
> >>> kernel to trace the irq masking sections.
> >> Don't we have the I-pipe tracer on this platform?
> >
> > Unfortunately, the tracer on arm has too much overhead to give
> > meaningful results.
>
> Hmm. Unless the system becomes unusable while running the tracer, I
> don't see the show-stopper yet. We are looking for an increase of the
> latency when triggering a certain event. That should remain measurable
> even if the base latency is far higher than usually.
>
> Do you know what makes the tracer so slow?
>
I suspected the fact that we disabled and enabled hardware irqs in
ipipe_get_tsc, but I reimplemented ipipe_get_tsc to not shut
interrupts off and the overhead of the tracer remains high.
--
Gilles Chanteperdrix
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