From: Anton Blanchard <anton@samba.org>
To: Michael Neuling <mikey@neuling.org>
Cc: Philippe Bergheaud <felix@linux.vnet.ibm.com>,
Linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] powerpc: memcpy optimization for 64bit LE
Date: Thu, 7 Nov 2013 13:07:03 +1100 [thread overview]
Message-ID: <20131107130703.482e8232@kryten> (raw)
In-Reply-To: <11438.1383718966@ale.ozlabs.ibm.com>
Hi,
> > 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?
Once booted the feature fixup code switches us over to the VMX copy
loops (which are already endian safe).
The question is what we do before that switch over. The base 64bit
memcpy takes alignment exceptions on POWER7 so we can't use it as is.
Fixing the causes of alignment exception would slow it down, because
we'd need to ensure all loads and stores are aligned either through
rotate tricks or bytewise loads and stores. Either would be bad for
all other 64bit platforms.
Anton
next prev parent reply other threads:[~2013-11-07 2:07 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
2013-11-07 2:10 ` Michael Neuling
2013-11-07 13:01 ` [PATCH v2] " Philippe Bergheaud
2013-11-07 2:07 ` Anton Blanchard [this message]
-- strict thread matches above, loose matches on Subject: below --
2014-04-29 23:10 [PATCH] " Anton Blanchard
2014-04-29 23:12 ` Anton Blanchard
2014-05-05 12:56 ` Philippe Bergheaud
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