From: Kenneth Johansson <kenneth@southpole.se>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "Albrecht Dreß" <albrecht.dress@arcor.de>, linuxppc-dev@ozlabs.org
Subject: Re: [PATCH] powerpc: tiny memcpy_(to|from)io optimisation
Date: Wed, 03 Jun 2009 16:36:36 +0200 [thread overview]
Message-ID: <1244039796.20864.48.camel@localhost.localdomain> (raw)
In-Reply-To: <1243983086.27194.7.camel@pasglop>
On Wed, 2009-06-03 at 08:51 +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2009-06-02 at 20:45 +0200, Albrecht Dreß wrote:
>
> >
> > which drops the r1 accesses, but still produces the sub-optimal loop.
> > Is this a gcc regression, or did I miss something here? Probably the
> > only bullet-proof way is to write some core loops in assembly... :-/
>
> Well, gcc may be right here. What you call the "optimal" loop uses the
> lwzu instruction. An interesting thing about this instruction is that
> it updates two GPRs at completion (I'm ignoring the load multiple and
> string instructions on purpose here).
> I wouldn't be surprised thus if the loop variant with the separate add
> ends up more efficient on most implementations around.
On an e300 core using the lwzu/stwu is about 20% faster so at least one
core prefer that optimization.
next prev parent reply other threads:[~2009-06-03 14:36 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-27 20:00 [PATCH] powerpc: tiny memcpy_(to|from)io optimisation Albrecht Dreß
2009-05-28 16:13 ` Joakim Tjernlund
2009-05-28 19:50 ` Albrecht Dreß
2009-05-29 6:31 ` Joakim Tjernlund
2009-05-31 10:11 ` Albrecht Dreß
2009-06-01 6:14 ` Joakim Tjernlund
2009-06-02 18:45 ` Albrecht Dreß
2009-06-02 22:51 ` Benjamin Herrenschmidt
2009-06-03 14:36 ` Kenneth Johansson [this message]
2009-06-03 18:35 ` Albrecht Dreß
2009-06-11 17:07 ` Wolfram Sang
2009-06-11 17:30 ` Grant Likely
2009-06-19 18:42 ` Lorenz Kolb
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