[rfc] boot-time async readahead...

[Daniel J Blueman]

On Thu, Feb 12, 2009 at 9:09 AM, Martin Pitt <martin.pitt at ubuntu.com> wrote:
> Daniel J Blueman [2009-02-12  0:57 +0000]:
>> By modifying the boot-time readahead to be at lower I/O and processor
>> priority than the boot scripts and asynchronous, I see a 20% reduction
>> in overall boot time (from installing bootchart) on my desktop: 41s
>> down to 33s.
>
> I tried it on my Dell Latitude D430, which has an utterly slow hard
> disk (25 MB/s read), and did stopwatch measurements of 4 cases:
> current jaunty readahead ("sync") and your readahead ("parallel"), as
> well as default readahead lists vs. an /etc/readahead/boot which
> contained the entire GNOME session.
[snip]

I strongly suspect that since the readahead requests are pre-sorted by
block and thus not in the bootscript-requested order, we get hurt.

I'll spin a -v2 in the next day or two to generate request-ordered
profiles, then not block-sort after. We need to leave the I/O
scheduling and elevator sorting to CFQ, but fire them in the right
order to get better temporal locality.

The current behaviour will be requesting GNOME libraries way before
they'll be needed. Let's see...

Daniel
-- 
Daniel J Blueman