From: Paul Mackerras <paulus@linuxcare.com>
To: FASSINO Jean-Philippe
<jeanphilippe.fassino@cnet.francetelecom.fr>,
"linuxppc-dev@lists.linuxppc.org"
<linuxppc-dev@lists.linuxppc.org>
Subject: Re: Patch for optimize context switch
Date: Tue, 22 Feb 2000 10:12:59 +1100 [thread overview]
Message-ID: <00022210165901.14669@argo.linuxcare.com.au> (raw)
In-Reply-To: 38B1183A.AC6214E0@cnet.francetelecom.fr
On Mon, 21 Feb 2000, FASSINO Jean-Philippe wrote:
> The aim of this patch is to optimize context switch on PPC.
> It permit to optimize pipeline and reduce near 30 instructions per
> context switch.
> I'm using it on my computer and it work well, please test it !
Interesting. How much does it reduce the context switch time? Did you
run lmbench or something to see if it makes it go faster?
The reason I ask is that it is possible that unrolling the loop as you
have done could actually make it go slower due to increased i-cache
misses. The bdnz instruction on PPC has essentially zero overhead since it
is pulled out of the instruction stream in the fetch/decode unit by the
branch processing unit. Also, it is very easy to predict whether a bdnz
will branch or not.
--
Paul Mackerras, Senior Open Source Researcher, Linuxcare, Inc.
+61 2 6262 8990 tel, +61 2 6262 8991 fax
paulus@linuxcare.com.au, http://www.linuxcare.com.au/
Linuxcare. Support for the revolution.
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2000-02-21 23:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-02-21 10:49 Patch for optimize context switch FASSINO Jean-Philippe
2000-02-21 23:12 ` Paul Mackerras [this message]
2000-02-22 9:27 ` Gabriel Paubert
2000-02-22 10:50 ` Benjamin Herrenschmidt
2000-02-22 11:13 ` Gabriel Paubert
2000-02-22 9:30 ` FASSINO Jean-Philippe
2000-02-22 11:23 ` FASSINO Jean-Philippe
2000-02-22 11:33 ` FASSINO Jean-Philippe
2000-02-22 11:50 ` Gabriel Paubert
2000-02-22 11:40 ` Gabriel Paubert
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