> zach.brown> that path before the recent dio completion patch set. We
> zach.brown> shouldn't expect significant performance regression from
> zach.brown> returning to the behaviour that existed before the completion
> zach.brown> clean up work.
>
> Are you going to quantify this at all? I think we should.
I spotted some free time on an old dual athlon and got an initial look
at the cpu cost of the dio cleanup patches currently in -mm.
I ran two aio-stress instances doing O_DIRECT 64k sequential reads and
writes to an existing 1gig file on ext3 on an old pata drive. I ran a
pair of cycle soakers measuring cpu load every second. After trimming
out the 8 highest and lowest samples the remaining samples were
averaged. I did this three times against 2.6.19-rc4-mm1 before and
after applying the dio-* patches.
before: 5.02% 5.23% 5.27%
after: 5.27% 5.33% 5.32%
So I'm not *gravely* concerned that we've regressed, but it'd be nice to
measure the impact of the dio-* patches on more capable hardware.
- z
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