linux-kernel - Re: [RFC] LZO de/compression support

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Date:	Fri, 25 May 2007 14:45:16 -0400
From:	Daniel Hazelton <dhazelton@...er.net>
To:	Richard Purdie <richard@...nedhand.com>
Cc:	Satyam Sharma <satyam.sharma@...il.com>,
	Nitin Gupta <nitingupta910@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm-cc@...top.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Panin <pazke@...pac.ru>, Bret Towe <magnade@...il.com>,
	Michael-Luke Jones <mlj28@....ac.uk>
Subject: Re: [RFC] LZO de/compression support - take 4

On Friday 25 May 2007 12:55:21 Daniel Hazelton wrote:
<snip>
> As to the performance - I can see absolutely no reason why the minimal
> version shouldn't perform the same (or better). The kernel codes memset and
> memcpy routines have been heavily tested *and* optimized over the years and
> moving from macro's to inline functions shouldn't have impacted performance
> at all. I will be testing the two code bases myself in a little bit - I'm
> more than a little paranoid and don't like the idea of trusting anyone with
> a "competing project" for all testing.

I'll have to better instrument my test code (a real quick (userspace) hack) 
using the minimized LZO1X implementation (take 4 :) and the complete LZOv2 
library (lzo1x_1_11_compress and the *unsafe* version of the decompressor 
used) but preliminary testing using just "time ./test" - the differences I've 
seen might be because I'm directly including one version of the code and the 
other is in a shared library. But even if I discount the system and user 
time - going *only* by the "real" time value I get results across 10 runs 
that differ by less than 0.001s - the average across 10 runs of the stripped 
down LZO code is about 0.00133s where the LZO library (liblzo2) returns about 
even performance - average is 0.001s.

A total difference of *ONE* *THIRD* of *ONE* *THOUSANDTH* of a second. With 
the better performance being in-kernel should bring, I can see no reason for 
a "big" difference.

If anyone's interested in the code I used for the test, let me know and I'll 
make it available.

DRH
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