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Date: Wed, 08 Oct 2008 10:39:31 -0500
From: Bill Gatliff <bgat@billgatliff.com>
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To: Dominik Bozek <domino@mikroswiat.pl>
Subject: Re: performance: memcpy vs. __copy_tofrom_user
References: <48ECC611.3030309@mikroswiat.pl>
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Dominik Bozek wrote:
> Hi all,
> 
> I have done a test of memcpy() and __copy_tofrom_user() on the mpc8313.
> And the major conclusion is that __copy_tofrom_user is more efficient
> than memcpy. Sometimes about 40%.

Have you looked at the two implementations?  I'm not as well-versed on PPC as
ARM, but I know the latter's __copy_* functions are optimized to be almost
unintelligible.  If your benchmark memcpy() implementation isn't, then you
aren't comparing apples-to-apples.

40% improvement is within what I could imagine getting from a hand-crafted,
no-holds-barred memcpy() implementation.  I'd look more carefully at that code.


b.g.
-- 
Bill Gatliff
bgat@billgatliff.com