Messages in this thread | | | Date | Wed, 8 Dec 2004 08:36:37 +0100 | From | Jens Axboe <> | Subject | Re: Time sliced CFQ io scheduler |
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On Tue, Dec 07 2004, Andrew Morton wrote: > Jens Axboe <axboe@suse.de> 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...
-- Jens Axboe
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