From: Scott Wood <scottwood@freescale.com>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
<linuxppc-dev@lists.ozlabs.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 2/2] powerpc32: optimise csum_partial() loop
Date: Wed, 5 Aug 2015 21:31:41 -0500 [thread overview]
Message-ID: <1438828301.2097.126.camel@freescale.com> (raw)
In-Reply-To: <20150806003059.GD18479@gate.crashing.org>
On Wed, 2015-08-05 at 19:30 -0500, Segher Boessenkool wrote:
> On Wed, Aug 05, 2015 at 03:29:35PM +0200, Christophe Leroy wrote:
> > On the 8xx, load latency is 2 cycles and taking branches also takes
> > 2 cycles. So let's unroll the loop.
>
> This is not true for most other 32-bit PowerPC; this patch makes
> performance worse on e.g. 6xx/7xx/7xxx. Let's not!
Chips with a load latency greater than 2 cycles should also benefit from the
unrolling. Have you benchmarked this somewhere and seen it reduce
performance? Do you know of any 32-bit PPC chips with a load latency less
than 2 cycles?
-Scott
next prev parent reply other threads:[~2015-08-06 2:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-05 13:29 [PATCH v2 0/2] powerpc32: Optimise csum_partial() Christophe Leroy
2015-08-05 13:29 ` [PATCH v2 1/2] powerpc32: optimise a few instructions in csum_partial() Christophe Leroy
2015-08-05 13:29 ` [PATCH v2 2/2] powerpc32: optimise csum_partial() loop Christophe Leroy
2015-08-06 0:30 ` Segher Boessenkool
2015-08-06 2:31 ` Scott Wood [this message]
2015-08-06 4:39 ` Segher Boessenkool
2015-08-06 22:45 ` Scott Wood
2015-08-06 23:25 ` Segher Boessenkool
2015-08-17 10:56 ` leroy christophe
2015-08-17 11:00 ` leroy christophe
2015-08-17 13:05 ` leroy christophe
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