Re: [PATCH] cfq-prio #2

[Nick Piggin]

Jens Axboe wrote:

> On Tue, Nov 11 2003, Nick Piggin wrote:
>
> > Jens Axboe wrote:
> >
> >
> > > Hi,
> > Hi Jens
> >
> >
> > > @@ -1553,6 +1559,10 @@
> > > 	struct io_context *ioc = get_io_context(gfp_mask);
> > >
> > > 	spin_lock_irq(q->queue_lock);
> > > +
> > > +	if (!elv_may_queue(q, rw))
> > > +		goto out_lock;
> > > +
> > > 	if (rl->count[rw]+1 >= q->nr_requests) {
> > > 		/*
> > > 		 * The queue will fill after this allocation, so set it as
> > > @@ -1566,15 +1576,12 @@
> > > 		}
> > > 	}
> > >
> > > -	if (blk_queue_full(q, rw)
> > > -			&& !ioc_batching(ioc) && !elv_may_queue(q, rw)) {
> > I know I hijacked elv_may_queue from you... any chance we could seperate
> > these so our schedulers can live in peace? ;)
>
> IOW, you completely broke it! I'm just changing it back to the
> original. When was this done, btw? Just discovered it when updating the
> patch. Pretty annoying...

You acked the change actually :P
I guess it was done in mainline when AS was merged.

> > Maybe my version should be called elv_force_queue?
>
> I just hate to see more of these, really. The original idea for
> may_queue was just that, may this process queue io or not. We can make
> it return something else, though, to indicate whether the process must
> be able to queue. Is it really needed?

Its quite important. If the queue is full, and AS is waiting for a process
to submit a request, its got a long wait.

Maybe a lower limit for per process nr_requests. Ie. you may queue if this
queue has less than 128 requests _or_ you have less than 8 requests
outstanding. This would solve my problem. It would also give you a much more
appropriate scaling for server workloads, I think. Still, thats quite a
change in behaviour (simple to code though).


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