From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: cutaway@bellsouth.net
Cc: Adrian Bunk <bunk@stusta.de>, linux-kernel@vger.kernel.org
Subject: Re: kernel optimization
Date: Sat, 23 Jul 2005 20:50:36 +0100 [thread overview]
Message-ID: <1122148237.27629.1.camel@localhost.localdomain> (raw)
In-Reply-To: <01bd01c58f50$0998c650$2800000a@pc365dualp2>
On Sad, 2005-07-23 at 02:30 -0400, cutaway@bellsouth.net wrote:
> Larger does not always mean slower. If it did, nobody would implement a
> loop unrolling optimization.
Generally speaking nowdays it does. Almost all loop unrolls are a loss
on PIV.
> 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.
You are comparing with very expensive jump operations its an unusual
case. For the majority of situations the TLB/cache overhead of misses
vastly outweighs the odd clock cycle gained by verbose output.
next prev parent reply other threads:[~2005-07-23 19:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-22 18:55 kernel optimization 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
2005-07-23 19:50 ` Alan Cox [this message]
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
-- strict thread matches above, loose matches on Subject: below --
2005-07-27 3:53 Al Boldi
2005-07-27 4:20 ` Lee Revell
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