Messages in this thread | | | Date | Tue, 19 Dec 2006 12:07:14 +0545 | From | "Manish Regmi" <> | Subject | Re: Linux disk performance. |
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On 12/18/06, Erik Mouw <mouw@nl.linux.org> wrote: <...snip...> > > > > But isn't O_DIRECT supposed to bypass buffering in Kernel? > > It is. > > > Doesn't it directly write to disk? > > Yes, but it still uses an IO scheduler. >
Ok. but i also tried with noop to turnoff disk scheduling effects. There was still timing differences. Usually i get 3100 microseconds but upto 20000 microseconds at certain intervals. I am just using gettimeofday between two writes to read the timing.
> In your first message you mentioned you were using an ancient 2.6.10 > kernel. That kernel uses the anticipatory IO scheduler. Update to the > latest stable kernel (2.6.19.1 at time of writing) and it will default > to the CFQ scheduler which has a smoother writeout, plus you can give > your process a different IO scheduling class and level (see > Documentation/block/ioprio.txt).
Thanks... i will try with CFQ.
Nick Piggin: > but > they look like they might be a (HZ quantised) delay coming from > block layer plugging.
Sorry i didn´t understand what you mean.
To minimise scheduling effects i tried giving it maximum priority.
-- --------------------------------------------------------------- regards Manish Regmi
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