Re: top hogs CPU in 2.6: kallsyms_lookup is very slow

From: Denis Vlasenko
Date: Fri Sep 17 2004 - 05:56:22 EST


On Thursday 16 September 2004 15:17, William Lee Irwin III wrote:
> At some point in the past, I wrote:
> >> As for all syscalls/etc. being slower by 50%-100%, I suggest toning
>
> On Thu, Sep 16, 2004 at 02:57:08PM +0300, Denis Vlasenko wrote:
> > s/all/many/:
> > uname <0.000142> ? ? ? ? ? ? ? uname <0.000217> 25% slower
> > brk <0.000176> ? ? ? ? ? ? ? ? brk <0.000174> no change
> > open <0.000218> ? ? ? ? ? ? ? ?open <0.000335> 33% slower
> > fstat64 <0.000104> ? ? ? ? ? ? fstat64 <0.000191> 90% slower
> > or maybe strace simply isn't very accurate and adds signinficant
> > noise to the measured delta?
>
> Could you try to estimate the resolution of whatever timer strace uses?
>
> At some point in the past, I wrote:
> >> down HZ (we desperately need to go tickless) and seeing if it persists.
> >> Also please check that time isn't twice as fast as it should be in 2.6.
>
> On Thu, Sep 16, 2004 at 02:57:08PM +0300, Denis Vlasenko wrote:
> > I recompiled 2.6 with HZ=100. It's not it.
> > Time is running normally too.
>
> Did the kallsyms patches reduce the cpu overhead from get_wchan()?

Yes. top does not hog CPU anymore. It takes even a liitle bit *less*
CPU than in 2.4 now.
--
vda

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