From: Dominik Bozek <domino@mikroswiat•pl>
To: Paul Mackerras <paulus@samba•org>
Cc: linuxppc-dev@ozlabs•org, linuxppc-embedded@ozlabs•org
Subject: Re: performance: memcpy vs. __copy_tofrom_user
Date: Fri, 10 Oct 2008 19:17:29 +0200 [thread overview]
Message-ID: <48EF8E29.1020101@mikroswiat.pl> (raw)
In-Reply-To: <18669.58803.48011.686743@cargo.ozlabs.ibm.com>
Paul Mackerras wrote:
> Very interesting. Can you work out where memcpy is being called on
> the network data? I wouldn't have expected that.
Ok. I've some results.
I done two test with different MTU. In both cases, about 0.5GB in total
has been transfered over network. Large blocks.
The test didn't trace a "shallow copy", where occasionally memcpy() is
also in use.
1) MTU=1500 (on both host and mpc8313)
* achieved throughput: 22MB/s (from mpc), 16MB/s (to mpc)
* total size of copied data by memcpy() was 37.6MB
* 96% of that has been copied by skb_clone(): 787758 times in blocks of 48B.
* about 3% of that has been copied by skb_copy_bits(): 1013 times, the
block size vary but rather bigger like 1300B.
* about 1% of that has been copied by eth_header(): 80248 times in
blocks of 6B (!!!!).
2) MTU=9000 (on both host and mpc8313)
* achieved throughput: 50MB/s (from mpc), 44MB/s (to mpc)
* total size of copied data by memcpy() was 6.4MB
* 97% of that has been copied by skb_clone(): 134260 times in blocks of 48B.
* 3% (whole rest) has been copied by eth_header(): 32912 times in blocks
of 6B.
Conclusion. Need for optimized memcpy() for blocks 48B and 6B :). Joke.
I said earlier, that I got about 10% boost when I replaced memcpy() by
__copy_tofrom_user(). It was the case with MTU 9000 because I work with
that setting in my environment.
I don't know when __copy_tofrom_user get faster than memcpy on other
cpus than mpc8313, but on mpc8313 48B blocks are more suitable for
__copy_tofrom_user.
Dominik
next prev parent reply other threads:[~2008-10-10 17:17 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 [this message]
2008-10-08 17:40 ` Scott Wood
2008-10-09 2:36 ` Paul Mackerras
2008-10-11 22:32 ` Benjamin Herrenschmidt
2008-10-13 15:06 ` Scott Wood
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