[ILUG] Re: adaptive readahead

[Marcus Furlong]

Marcus Furlong wrote:

> Pádraig Brady wrote:
> 
>> Marcus Furlong wrote:
>>> Hi,
>>> 
>>> Having recently installed OpenSuse 10.1, I was surprised that it seems
>>> much more responsive and snappier than a gentoo installation on the same
>>> machine with processor-specific CFLAGS and prelinked binaries, etc. On
>>> the OpenSuse site they actually state that prelinking in some cases
>>> slows down applications, and they use an adaptive readahead technique. I
>>> was wondering if anyone could enlighten me as to the differences between
>>> the difference types of adaptive readahead that I've found:
>>> 
>>> *  There is Behdad Esfahbod's version completed last year for Google's
>>> SoC
>>>    (and used by Red Hat/Fedora I think)
>>> 
>>>    http://preload.sourceforge.net/
>>> 
>>> 
>>> *  There is SUSE's preload (which is not the same as the above one,
>>> despite
>>>    having the same version number, I compared the source for both)
>>> 
>>>    http://en.opensuse.org/SUPER_preloading
>>>    http://www.novell.com/products/linuxpackages/suselinux/preload.html
>>> 
>>> 
>>> *  Debian (and I suppose Ubuntu too?) uses ld.so.preload-manager
>>> 
>>>    http://packages.debian.org/stable/admin/ld.so.preload-manager
>>> 
>>> 
>>> *  Gentoo has readahead-list
>>>  
> http://packages.gentoo.org/packages/?category=sys-apps;name=readahead-list
>> 
>> ubuntu also has readahead-list. The above seem to do much the same thing:
>> In idle periods (when entering password for example), preload the
>> files off the disk that the user will probably need.
>> An interesting related thing just released will align those
>> files linearly in a dedicated partition, so that there will
>> be no disk seeking when loading those files:
>> http://lkml.org/lkml/2006/5/15/46
> 
> Interesting. Might give it a whirl.

Just as a followup to this, I found a little howto for fcache here ->
http://gentoo-wiki.com/HOWTO_FCache

>>> Ok so I was wondering if all the above are doing the same thing? If so,
>>> does anyone know which one does it best? (SUSE 10.1 does seem very fast
>>> to me, but I'm not sure about the other distros)
>>> 
>>> Also, there is Wu Fengguang's kernel version of adaptive readahead:
>>> 
>>>    http://lkml.org/lkml/2006/5/27/71
>>> 
>>> which seems to give a 3x speedup in a simple test =>
>>> 
>>>    http://linux.inet.hr/adaptive_readahead_benchmark.html
>>> 
>>> Does this do the same thing as the above programs? Will it obsolete them
>>> if it accepted into the kernel?
>> 
>> This is more a runtime thing and is for automatically
>> reading disk blocks (probably within a file) that you'll probably need.
> 
> So this and the fcache module you mentioned could be used together? Wu's
> adaptive readahead could automatically read the disk blocks and fcache
> could also then store those blocks on the cache partition? Or are they
> mutually exclusive?
> 
>> 
>>> 
>>> There is also Con Kolivas's swap prefetch patchset at
>>> http://kernel.kolivas.org and the aforementioned prelink, but AFAIK
>>> those can be used along with adaptive readahead.
>> 
>> Make sure you don't confuse prelinking and preloading:
>> http://crast.us/james/articles/prelink.php
> 
> Yeah, I already use prelinking (and have found it to speed up things,
> possibly in my mind though! :-P) but on http://en.opensuse.org/SUPER, they
> state:
> 
> "SUPER standard benchmark has been expanded with some additional tests
> based on our 1 CD install. Some areas like booting .are improved,
> preloading has made already a big difference in application startup time
> and prelinking is actually making things certainly slower again. Very
> interesting results indeed. Check it out. Coolo sure was right about
> prelink how could I have doubted the master?"
> 
> So, I started looking around at the various preloading programs. Anyone
> know the best way of benchmarking these things? bootchart and `time` come
> to mind.
> 
>> 
>> Pádraig.
> 
>