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:

quoted

On Tue, 9 Jan 2007, Fengguang Wu wrote:

quoted

quoted

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

quoted

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