[dm-devel] Re: IO scheduler based IO controller V10

[Jens Axboe <jens axboe oracle com>]

On Sat, Oct 03 2009, Mike Galbraith wrote:
> On Sat, 2009-10-03 at 09:24 +0200, Jens Axboe wrote:
> 
> > After shutting down the computer yesterday, I was thinking a bit about
> > this issue and how to solve it without incurring too much delay. If we
> > add a stricter control of the depth, that may help. So instead of
> > allowing up to max_quantum (or larger) depths, only allow gradual build
> > up of that the farther we get away from a dispatch from the sync IO
> > queues. For example, when switching to an async or seeky sync queue,
> > initially allow just 1 in flight. For the next round, if there still
> > hasn't been sync activity, allow 2, then 4, etc. If we see sync IO queue
> > again, immediately drop to 1.
> > 
> > It could tie in with (or partly replace) the overload feature. The key
> > to good latency and decent throughput is knowing when to allow queue
> > build up and when not to.
> 
> Hm.  Starting at 1 sounds a bit thin (like IDLE), multiple iterations to
> build/unleash any sizable IO, but that's just my gut talking.

Not sure, will need some testing of course. But it'll build up quickly.

-- 
Jens Axboe