From: <cutaway@bellsouth.net>
To: "Adrian Bunk" <bunk@stusta.de>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: kernel optimization
Date: Sat, 23 Jul 2005 02:30:31 -0400 [thread overview]
Message-ID: <01bd01c58f50$0998c650$2800000a@pc365dualp2> (raw)
In-Reply-To: <20050722201416.GM3160@stusta.de>
----- Original Message -----
From: "Adrian Bunk" <bunk@stusta.de>
To: "christos gentsis" <christos_gentsis@yahoo.co.uk>
Cc: <linux-kernel@vger.kernel.org>
Sent: Friday, July 22, 2005 16:14
Subject: Re: kernel optimization
>
> It's completely untested.
> And since it's larger, it's also slower.
Larger does not always mean slower. If it did, nobody would implement a
loop unrolling optimization.
ex. Look at how GCC generates jump tables for switch() when there's about
10-12 (or more) case's sparsely scattered in the rage from 0 through 255.
It generates a 256 element directly indexed jump table (obviously with many
duplicate entries). This is faster than a cascaded if/else
construct(particularly for those that would have been on the end of the
if/else chain), but it is a very large construct. You'll see some of these
"plump" switches generated in various SCSI drivers and in the VT102
emulation if you disassemble them.
next prev parent reply other threads:[~2005-07-23 6:30 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-22 18:55 christos gentsis
2005-07-22 19:52 ` David Lang
2005-07-22 20:15 ` Adrian Bunk
2005-07-22 20:14 ` Adrian Bunk
2005-07-22 21:11 ` christos gentsis
2005-07-23 14:34 ` Simon Strandman
2005-07-23 5:35 ` Al Boldi
2005-07-23 6:30 ` cutaway [this message]
2005-07-23 19:50 ` Alan Cox
2005-07-23 22:03 ` cutaway
[not found] <200507231849.j6NInMPO003728@laptop11.inf.utfsm.cl>
2005-07-26 5:22 ` Al Boldi
2005-07-26 9:22 ` Adrian Bunk
2005-07-27 3:53 Al Boldi
2005-07-27 4:20 ` Lee Revell
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