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SubjectRe: Reiser4 und LZO compression
Nigel Cunningham wrote:
> Hi.
> On Tue, 2006-08-29 at 03:23 -0500, David Masover wrote:
>>Nigel Cunningham wrote:
>>>On Tue, 2006-08-29 at 06:05 +0200, Jan Engelhardt wrote:
>>>>>>>>Hmm. LZO is the best compression algorithm for the task as measured by
>>>>>>>>the objectives of good compression effectiveness while still having very
>>>>>>>>low CPU usage (the best of those written and GPL'd, there is a slightly
>>>>>>>>better one which is proprietary and uses more CPU, LZRW if I remember
>>>>>>>>right. The gzip code base uses too much CPU, though I think Edward made
>>>>>>>I don't think that LZO beats LZF in both speed and compression ratio.
>>>>>>>LZF is also available under GPL (dual-licensed BSD) and was choosen in favor
>>>>>>>of LZO for the next generation suspend-to-disk code of the Linux kernel.
>>>>>>thanks for the info, we will compare them
>>>>>For Suspend2, we ended up converting the LZF support to a cryptoapi
>>>>>plugin. Is there any chance that you could use cryptoapi modules? We
>>>>>could then have a hope of sharing the support.
>>>>I am throwing in gzip: would it be meaningful to use that instead? The
>>>>decoder (inflate.c) is already there.
>>>>06:04 shanghai:~/liblzf-1.6 > l configure*
>>>>-rwxr-xr-x 1 jengelh users 154894 Mar 3 2005 configure
>>>>-rwxr-xr-x 1 jengelh users 26810 Mar 3 2005 configure.bz2
>>>>-rw-r--r-- 1 jengelh users 30611 Aug 28 20:32 configure.gz-z9
>>>>-rw-r--r-- 1 jengelh users 30693 Aug 28 20:32 configure.gz-z6
>>>>-rw-r--r-- 1 jengelh users 53077 Aug 28 20:32 configure.lzf
>>>We used gzip when we first implemented compression support, and found it
>>>to be far too slow. Even with the fastest compression options, we were
>>>only getting a few megabytes per second. Perhaps I did something wrong
>>>in configuring it, but there's not that many things to get wrong!
>>All that comes to mind is the speed/quality setting -- the number from 1
>>to 9. Recently, I backed up someone's hard drive using -1, and I
>>believe I was still able to saturate... the _network_. Definitely try
>>again if you haven't changed this, but I can't imagine I'm the first
>>persson to think of it.
>> From what I remember, gzip -1 wasn't faster than the disk. But at
>>least for (very) repetitive data, I was wrong:
>>eve:~ sanity$ time bash -c 'dd if=/dev/zero of=test bs=10m count=10; sync'
>>10+0 records in
>>10+0 records out
>>104857600 bytes transferred in 3.261990 secs (32145287 bytes/sec)
>>real 0m3.746s
>>user 0m0.005s
>>sys 0m0.627s
>>eve:~ sanity$ time bash -c 'dd if=/dev/zero bs=10m count=10 | gzip -v1 >
>>test; sync'
>>10+0 records in
>>10+0 records out
>>104857600 bytes transferred in 2.404093 secs (43616282 bytes/sec)
>> 99.5%
>>real 0m2.558s
>>user 0m1.554s
>>sys 0m0.680s
>>eve:~ sanity$
>>This was on OS X, but I think it's still valid -- this is a slightly
>>older Powerbook, with a 5400 RPM drive, 1.6 ghz G4.
>>-1 is still worlds better than nothing. The backup was over 15 gigs,
>>down to about 6 -- loads of repetitive data, I'm sure, but that's where
>>you win with compression anyway.
> Wow. That's a lot better; I guess I did get something wrong in trying to
> tune deflate. That was pre-cryptoapi though; looking at
> cryptoapi/deflate.c, I don't see any way of controlling the compression
> level. Am I missing anything?

zlib is tunable, not cryptoapi's deflate.
look at zlib_deflateInit2()

>>Well, you use cryptoapi anyway, so it should be easy to just let the
>>user pick a plugin, right?
> Right. They can already pick deflate if they want to.
> Regards,
> Nigel

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