Re: [patch 10/10] Scheduler profiling - Use immediate values

Frank Ch. Eigler
2007-07-07T17:56:26Z

Hi, Adrian -

On Sat, Jul 07, 2007 at 07:01:57PM +0200, Adrian Bunk wrote:
> [...]
> > Things are not so simple. One might not know that one has a
> > performance problem until one tries some analysis tools. Rebooting
> > into different kernels just to investigate does not work generally [...]
>
> I'm not getting this:
>
> You'll only start looking into an analysis tool if you have a
> performance problem, IOW if you are not satisfied with the
> performance.

There may be people whose jobs entail continually suspecting
performance problems. Or one may run instrumentation code on a
long-term basis specifically to locate performance spikes.

> And the debug code will not have been tested on this machine no matter
> whether it's enabled through a compile option or at runtime.

There is a big difference in favour of the former. The additional
instrumentation code may be small enough to inspect carefully. The
rest of the kernel would be unaffected.

> [...] If you might be able to get a big part of tracing and other
> debug code enabled with a performance penalty of a few percent of
> _kernel_ performance, then you might get much debugging aid without
> any effective impact on application performance.

Agreed.

- FChE