Hi.
On Wed, 2007-01-10 at 09:57 +0800, Fengguang Wu wrote:
> On Tue, Jan 09, 2007 at 08:23:32AM -0800, Linus Torvalds wrote:
> >
> >
> > On Tue, 9 Jan 2007, Fengguang Wu wrote:
> > > >
> > > > The fastest and probably most important thing to add is some readahead
> > > > smarts to directories --- both to the htree and non-htree cases. If
> > >
> > > Here's is a quick hack to practice the directory readahead idea.
> > > Comments are welcome, it's a freshman's work :)
> >
> > Well, I'd probably have done it differently, but more important is whether
> > this actually makes a difference performance-wise. Have you benchmarked it
> > at all?
>
> Yes, a trivial test shows a marginal improvement, on a minimal debian system:
>
> # find / | wc -l
> 13641
>
> # time find / > /dev/null
>
> real 0m10.000s
> user 0m0.210s
> sys 0m4.370s
>
> # time find / > /dev/null
>
> real 0m9.890s
> user 0m0.160s
> sys 0m3.270s
>
> > Doing an
> >
> > echo 3 > /proc/sys/vm/drop_caches
> >
> > is your friend for testing things like this, to force cold-cache
> > behaviour..
>
> Thanks, I'll work out numbers on large/concurrent dir accesses soon.
I gave it a try, and I'm afraid the results weren't pretty.
I did:
time find /usr/src | wc -l
on current git with (3 times) and without (5 times) the patch, and got
with:
real 54.306, 54.327, 53.742s
usr 0.324, 0.284, 0.234s
sys 2.432, 2.484, 2.592s
without:
real 24.413, 24.616, 24.080s
usr 0.208, 0.316, 0.312s
sys: 2.496, 2.440, 2.540s
Subsequent runs without dropping caches did give a significant
improvement in both cases (1.821/.188/1.632 is one result I wrote with
the patch applied).
Regards,
Nigel
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