linux-kernel - Re: How git affects kernel.org performance

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Date:	Wed, 10 Jan 2007 09:57:39 +0800
From:	Fengguang Wu <fengguang.wu@...il.com>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Theodore Tso <tytso@....edu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Andrew Morton <akpm@...l.org>, Willy Tarreau <w@....eu>,
	"H. Peter Anvin" <hpa@...or.com>, git@...r.kernel.org,
	nigel@...el.suspend2.net, "J.H." <warthog9@...nel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Pavel Machek <pavel@....cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	webmaster@...nel.org,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: How git affects kernel.org performance

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.

Regards,
Wu
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