Messages in this thread | | | From | Denis Vlasenko <> | Subject | Re: top hogs CPU in 2.6: kallsyms_lookup is very slow | Date | Thu, 16 Sep 2004 14:57:08 +0300 |
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> > 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
Thanks.
> As for all syscalls/etc. being slower by 50%-100%, I suggest toning
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?
> 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.
I recompiled 2.6 with HZ=100. It's not it. Time is running normally too. -- vda
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