Re: Reiser4 und LZO compression

[David Masover <ninja@slaphack.com>]

Nigel Cunningham wrote:
> Hi.
>
> 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.
> > > > >
> > > > > see: http://www.goof.com/pcg/marc/liblzf.html
> > > > 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.

Well, you use cryptoapi anyway, so it should be easy to just let the 
user pick a plugin, right?
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