Re: [PATCH] cfq-prio #2

[Jens Axboe <axboe@suse.de>]

On Tue, Nov 11 2003, Nick Piggin wrote:
> 
> 
> Jens Axboe wrote:
> 
> >On Tue, Nov 11 2003, Nick Piggin wrote:
> >
> >>
> >>You acked the change actually :P
> >>I guess it was done in mainline when AS was merged.
> >>
> >
> >Probably missed the semantic change of may_queue.
> >
> 
> Anyway I won't bother digging up the email, its been done now.

Yeah too late to change now...

> >>>>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).
> >>
> >
> >That basically belongs inside your may_queue for the io scheduler, imo.
> >
> 
> You can force it to disallow the request, but you can't force it to allow
> one (depending on a successful memory allocation, of course).

Well that's back two mails then, make may_queue return whether you must
queue, may queue, or can't queue.

-- 
Jens Axboe