Re: [RFC V2 PATCH 2/5] cfq-iosched: preparation to handle multiple service trees

[Jeff Moyer <jmoyer@redhat.com>]

Corrado Zoccolo <czoccolo@gmail.com> writes:

> Hi Jeff,
> On Wed, Oct 21, 2009 at 5:31 PM, Jeff Moyer <jmoyer@redhat.com> wrote:
>> Corrado Zoccolo <czoccolo@gmail.com> writes:
>>
>>> We embed a pointer to the service tree in each queue, to handle multiple
>>> service trees easily.
>>> Service trees are enriched with a counter.
>>> cfq_add_rq_rb is invoked after putting the rq in the fifo, to ensure
>>> that all fields in rq are properly initialized.
>>>
>>> @@ -115,6 +116,9 @@ struct cfq_queue {
>>>       unsigned short ioprio_class, org_ioprio_class;
>>>
>>>       pid_t pid;
>>> +
>>> +     struct cfq_rb_root *service_tree;
>>> +     struct cfq_io_context *cic;
>>>  };
>>
>> This change worries me.  For async queues, there is not a 1:1 mapping
>> between cfqq and cic.
>
> Currently, I need it only for sync queues. And it is used only to
> determine if a queue is seeky, so if we can mark it in the queue
> instead of the cic, this will not be needed any more.

Ah ha!  I have the same requirement for breaking the queues apart, so I
think this won't be an issue.

Thanks!
Jeff