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SubjectRe: [PATCH] kprobes - do not allow optimized kprobes in entry code
On Sun, Feb 20, 2011 at 01:59:48PM +0100, Ingo Molnar wrote:
>
> * Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> wrote:
>
> > Thanks, I've also tested. (But my machine has no L1-icache-prefetches* support)
> > What I can tell is both of L1-icache-load and L1-icache-load-misses is reduced by
> > the patch. ;-)
>
> That's actually a pretty interesting result: it means that compressing entry code
> into a single section compresses the icache footprint in a measurable way. The
> icache miss rate went down by about 6%:
>
> > 1,234,272 L1-icache-load-misses ( +- 0.105% )
> > 1,155,816 L1-icache-load-misses ( +- 0.113% )
>
> Which, assuming that there's no kernel build and bootup related skew effect that is
> larger than 2-3% means that this is an improvement.
>
> perf feature request: would be nice if it was able to do:
>
> perf stat --record ...
> perf diff
>
> and it would show a comparison of the two runs.
>
> In hindsight it makes sense: the patch probably reduced the fragmentation of the
> icache for this workload.
>
> But it's still surprising :-)
>
> Mind splitting the patch up into two parts, the first one that does the performance
> optimization intentionally (with numbers, explanation, etc.), the second one that
> uses the new section for kprobes exclusion?
np, I'll send v2 shortly

thanks,
jirka

>
> Thanks,
>
> Ingo


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