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

[William Lee Irwin III <wli@holomorphy.com>]

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()? I take
this to mean reducing HZ to 100 did not alleviate the syscall problems?
How do microbenchmarks fare, e.g. lmbench?


-- wli