Re: [PATCH] SFQ disk scheduler

[Andrea Arcangeli]

On Mon, Feb 10, 2003 at 03:50:01PM +0100, Jens Axboe wrote:
> Hi,
> 
> Here's a simple stochastic fairness queueing disk scheduler, for current
> 2.5.59-BK. It has known limitations right now, mainly because I didn't
> bother making it complete. But it should suffice for some rudimentary
> testing, at least.

Cool, that was fast! ;)

> 
> I'm not going to go into great detail about how it works, see Andrea's
> initial post of the paper referenced. This version may not be completely
> true to the SFQ concept, but should be close enough I think. It divides
> traffic into a fixed number of buckets (64 per default), and perturbs
> the hash every 5 seconds (hash shamelessly borrowed from networking atm,
> see comment).

I tend to think 5 seconds is too small, 30 sec would be better IMHO (it
should be tested at bit).

> To avoid too many disk seeks, when it's time to dispatch requests to the
> driver, we round robin all non-empty buckets and grab a single request
> from each. These requests are sorted into the dispatch queue.
> 
> For performance reasons, io scheduler request merging is still a
> per-queue function (and not per-bucket).

Unsure if it worth, but it probably it won't make that much difference,
likely different workloads are working on different part of the disk
anyways.

> In closing, let me stress that this version has not really been tested
> all that much. It passes simple SCSI and IDE testing, should work on any
> hardware basically.

How does it feel?

Andrea