Re: [PATCH v3 0/5]add new ioctls to do metadata readahead in btrfs

[Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>]

On Thu, 20 Jan 2011 10:34:18 +0800 Shaohua Li <shaohua.li-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:

> > >   Under a harddisk based netbook with Meego, the metadata readahead
> > > reduced about 3.5s boot time in average from total 16s.
> > 
> > That's a respectable speedup.  And it *needs* to be a good speedup,
> > given how hacky all of this is!
> > 
> > But then..  reducing bootup time on a laptop/desktop/server by 3.5s
> > isn't exactly a world-shattering benefit, is it?  Is it worth all the
> > hacky code?
> a laptop/desktop/server need read more data from hard disks, this will
> give more bootup time saving I think, though not tested yet.

Well, the whole point of the patch is to improve boot times, so the
more boot-time testing you can do, the better that is!

> > It would be much more valuable if those 3.5 seconds were available to
> > devices which really really care about bootup times, but very few of
> > those devices use rotating disks nowadays, I expect?
> Currently most popular netbooks are using rotating disks actually. And
> this will benefit laptop/desktop too.

But my point is that three seconds boot-time improvement for a system
which has an uptime of days or months isn't terribly exciting.

What *would* be terribly exciting is a three-second improvement for
cameras, cellphones, etc.  But they don't use spinning disks.

Can we expect *any* benefit for flash-type storage devices?  If so, how
much?