From: Philippe Bergheaud <felix@linux.vnet.ibm.com>
To: Michael Neuling <mikey@neuling.org>
Cc: Linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc: memcpy optimization for 64bit LE
Date: Wed, 06 Nov 2013 11:21:51 +0100 [thread overview]
Message-ID: <527A183F.7030500@linux.vnet.ibm.com> (raw)
In-Reply-To: <11438.1383718966@ale.ozlabs.ibm.com>
Michael Neuling wrote:
> Philippe Bergheaud <felix@linux.vnet.ibm.com> wrote:
>
>
>>Unaligned stores take alignment exceptions on POWER7 running in little-endian.
>>This is a dumb little-endian base memcpy that prevents unaligned stores.
>>It is replaced by the VMX memcpy at boot.
>
>
> Is this any faster than the generic version?
The little-endian assembly code of the base memcpy is similar to the code emitted by gcc when compiling the generic memcpy in lib/string.c, and runs at the same speed.
However, a little-endian assembly version of the base memcpy is required (as opposed to a C version), in order to use the self-modifying code instrumentation system.
After the cpu feature CPU_FTR_ALTIVEC is detected at boot, the slow base memcpy is nop'ed out, and the fast memcpy_power7 is used instead.
Philippe
next prev parent reply other threads:[~2013-11-06 10:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-05 8:38 [PATCH] powerpc: memcpy optimization for 64bit LE Philippe Bergheaud
2013-11-06 6:22 ` Michael Neuling
2013-11-06 10:21 ` Philippe Bergheaud [this message]
2013-11-07 2:10 ` Michael Neuling
2013-11-07 13:01 ` [PATCH v2] " Philippe Bergheaud
2013-11-07 2:07 ` [PATCH] " Anton Blanchard
-- strict thread matches above, loose matches on Subject: below --
2014-04-29 23:10 Anton Blanchard
2014-04-29 23:12 ` Anton Blanchard
2014-05-05 12:56 ` Philippe Bergheaud
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