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Message-ID: <787b0d920607131006p5f55c9c7veadb840042a10ba@mail.gmail.com>
Date: Thu, 13 Jul 2006 13:06:32 -0400
From: "Albert Cahalan" <acahalan@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH] Use uname not sysctl to get the kernel revision
Cc: ak@suse.de, tytso@mit.edu, drepper@redhat.com, arjan@infradead.org,
       rdunlap@xenotime.net, akpm@osdl.org, linux-kernel@vger.kernel.org,
       libc-alpha@sourceware.org
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On 7/13/06, Eric W. Biederman <ebiederm@xmission.com> wrote:
> "Albert Cahalan" <acahalan@gmail.com> writes:

> > Matching keywords, as is needed for /proc/*/status,
> > is also horribly slow. I ended up using gperf to make
> > a perfect hash table, then gcc's computed goto for
> > jumping to the code, and it still wasn't cheap to do.
> > (while /sys lacks this, the extra open-read-close is
> > certain to be far worse)
>
> I agree matching keywords and such seems slow.
>
> If the only overhead comes from open-read-close we can
> come up with a sys_readfile that doesn't need to actually
> open the file for one shot cases.

A sys_readfile would be great. It probably should
work like readlink. Supplying a struct stat without
a race condition would be good too.

Note that /sys will still be needlessly slow because
of the one-item-per-file idea. One of the few good
things about /proc is that you can get a whole
struct full of data all at once.

Fixing one bottleneck just leads to the next. It's best
to fix all the anti-performance stupidity at once.