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

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Date:	Wed, 21 Oct 2009 12:27:26 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC V2 PATCH 2/5] cfq-iosched: preparation to handle multiple  service trees

Corrado Zoccolo <czoccolo@...il.com> writes:

> Hi Jeff,
> On Wed, Oct 21, 2009 at 5:31 PM, Jeff Moyer <jmoyer@...hat.com> wrote:
>> Corrado Zoccolo <czoccolo@...il.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
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