Re: [PATCH] cfq-prio #2

[Nick Piggin <piggin@cyberone.com.au>]

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.

>
>>>>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).