Message-ID: <41F5C6D4.4030106@redhat.com>
Date: Mon, 24 Jan 2005 20:11:00 -0800
From: Ulrich Drepper <drepper@redhat.com>
Organization: Red Hat, Inc.
User-Agent: Mozilla Thunderbird  (X11/20041216)
MIME-Version: 1.0
To: george@mvista.com
CC: Roland McGrath <roland@redhat.com>, Andrew Morton <akpm@osdl.org>,
       Linus Torvalds <torvalds@osdl.org>, linux-kernel@vger.kernel.org,
       Christoph Lameter <clameter@sgi.com>
Subject: Re: [PATCH 1/7] posix-timers: tidy up clock interfaces and consolidate
 dispatch logic
References: <200501232322.j0NNMcxe006476@magilla.sf.frob.com> <41F5ABB8.8070308@mvista.com>
In-Reply-To: <41F5ABB8.8070308@mvista.com>
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George Anzinger wrote:
> As I understand it modern machines, the indirect call does really bad 
> things to the pipeline.

Unless the call happens often, really often, you'll not be able to 
measure differences.  Indirect jump obviously cause pipeline stalls 
which often, but not always, can be avoided with direct calls.  But we 
are not talking here about huge delays.  And the delays are equivalent 
in cost to a mispredicted branch.  If you have a couple of ifs in a row 
you are likely to incur problems with the branch prediction.  I would 
just use the indirect jumps but if you want, do some timing and see 
whether you can filter the difference out of the noise.

-- 
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖

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