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

[William Lee Irwin III]

On Thu, Sep 16, 2004 at 02:28:26PM +0300, Denis Vlasenko wrote:
> I see 2.6.9-rc2 being slower than 2.4.27-rc3
> on a Pentium 66, 80 MB RAM.
> Specifically:
> top on idle machine sucks ~40% CPU while in 2.4
> it takes only ~6%
> I recompiled 2.6 with HZ=100 and with slab debugging
> off. This helped a bit (wget was slow too),
> but top still hogs CPU.
> I did 'strace -T -tt top b n 1' under both kernels,
> postprocessed it a bit:

The following patches in -mm are likely to help top(1).

kallsyms-data-size-reduction--lookup-speedup.patch
  kallsyms data size reduction / lookup speedup

inconsistent-kallsyms-fix.patch
  Inconsistent kallsyms fix

kallsyms-correct-type-char-in-proc-kallsyms.patch
  kallsyms: correct type char in /proc/kallsyms

kallsyms-fix-sparc-gibberish.patch
  kallsyms: fix sparc gibberish

As for all syscalls/etc. being slower by 50%-100%, I suggest toning
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.


-- wli
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