Re: ext3 IO latency measurements (was: Linux 2.6.29)

Linus Torvalds
2009-03-26T22:48:40Z

On Thu, 26 Mar 2009, Jan Kara wrote:
>
> Reads are measurably better with the patch - the test with cat you
> describe below took ~0.5s per file without the patch and always less than
> 0.02s with the patch. So it seems to help something.

That would seem to be a _huge_ improvement.

Reads are the biggest issue for starting a new process (eg starting
firefox while under load), and if cat'ing that small file improved by that
much, then I bet there's a huge practical implication for a lot of desktop
uses.

The fundamental fsync() latency problem we sadly can't help much with, the
way ext3 seems to work. But I do suspect that the whole "don't synchronize
with the journal for normal write-outs" may end up helping even fsync just
a bit, if only because I suspect it will improve writeout throughput too
and thus avoid one particular bottleneck.

Linus