Re: Higher than expected disk write(2) latency

From: Martin Sustrik
Date: Thu Jul 10 2008 - 09:17:42 EST


Hi Alan,

What we see is that AIO performs rather bad while we are still enqueueing more writes (it misses right position on the disk and has to do superfluous disk revolvings), however, once we stop enqueueing new write request, those already in the queue are processed swiftly.

Which disk scheduler are you using - some of the disk schedulers
intentionally delay writes to try and get better block merging.

It's CFQ. Does it delay writes? And if so, what should we use instead?

Thanks.
Martin
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