Re: Time sliced CFQ io scheduler
From: Jens Axboe
Date: Wed Dec 08 2004 - 02:49:10 EST
On Tue, Dec 07 2004, Andrew Morton wrote:
> Jens Axboe <axboe@xxxxxxx> wrote:
> > I think we need to end up with something that sets the machine profile
> > for the interesting disks. Some things you can check for at runtime
> > (like the writes being extremely fast is a good indicator of write
> > caching), but it is just not possible to cover it all. Plus, you end up
> > with 30-40% of the code being convoluted stuff added to detect it.
> We can detect these things from userspace. Parse the hdparm/scsiinfo
> output, then poke numbers into /sys tunables.
The simple things, like cache settings and queue depth - definitely. The
harder things like how does this drive behave you cannot. And
unfortunately the former is also pretty easy to control (at least for
the depth) and at least gather at runtime. So I think a user mode helper
only makes sense if it can help you with real drive characteristics that
are hard to detect. Plus, settings have a nack for changing while we
are running as well.
Hmm so perhaps not such a hot idea after all. I don't envision anyone
actually doing it anyways, so...
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