From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Scott Wood <scottwood@freescale.com>
Cc: linuxppc-dev@ozlabs.org, Dominik Bozek <domino@mikroswiat.pl>,
linuxppc-embedded@ozlabs.org
Subject: Re: performance: memcpy vs. __copy_tofrom_user
Date: Sun, 12 Oct 2008 09:32:07 +1100 [thread overview]
Message-ID: <1223764327.8157.185.camel@pasglop> (raw)
In-Reply-To: <48ECF08F.7000400@freescale.com>
On Wed, 2008-10-08 at 12:40 -0500, Scott Wood wrote:
>
> The performance difference most likely comes from the fact that copy
> to/from user can assume that the memory is cacheable, while memcpy is
> occasionally used on cache-inhibited memory -- so dcbz isn't used. We
> may be better off handling the alignment fault on those occasions, and
> we should use dcba on chips that support it.
Note that the kernel memcpy isn't supposed to be used for non-cacheable
memory. That's what memcpy_to/fromio are for.
But Paul has a point that for small copies especially, the cost of
the cache instructions outweigh their benefit.
Cheers,
Ben.
next prev parent reply other threads:[~2008-10-11 22:32 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-08 14:39 performance: memcpy vs. __copy_tofrom_user Dominik Bozek
2008-10-08 15:31 ` Minh Tuan Duong
2008-10-08 15:39 ` Bill Gatliff
2008-10-08 15:42 ` Grant Likely
2008-10-09 2:34 ` Paul Mackerras
2008-10-09 10:12 ` Dominik Bozek
2008-10-09 11:06 ` Paul Mackerras
2008-10-09 11:41 ` Dominik Bozek
2008-10-09 12:04 ` Leon Woestenberg
2008-10-09 15:37 ` Matt Sealey
2008-10-11 22:30 ` Benjamin Herrenschmidt
2008-10-12 2:05 ` Matt Sealey
2008-10-12 4:05 ` Benjamin Herrenschmidt
2008-10-13 15:20 ` Scott Wood
2008-10-13 20:50 ` Benjamin Herrenschmidt
2008-10-13 21:03 ` Scott Wood
2008-10-14 2:14 ` Matt Sealey
2008-10-14 2:39 ` Benjamin Herrenschmidt
2008-10-14 15:10 ` Scott Wood
2008-10-15 1:37 ` Matt Sealey
2008-10-10 17:17 ` Dominik Bozek
2008-10-08 17:40 ` Scott Wood
2008-10-09 2:36 ` Paul Mackerras
2008-10-11 22:32 ` Benjamin Herrenschmidt [this message]
2008-10-13 15:06 ` Scott Wood
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