On Fri, Jan 20 2017, Paolo Valente wrote:

quoted

Il giorno 17 gen 2017, alle ore 03:47, Jens Axboe [off-list ref] ha scritto:

On 12/22/2016 09:49 AM, Paolo Valente wrote:

quoted

quoted

Il giorno 17 dic 2016, alle ore 01:12, Jens Axboe [off-list ref] ha scritto:

This is basically identical to deadline-iosched, except it registers
as a MQ capable scheduler. This is still a single queue design.

One last question (for today ...):in mq-deadline there are no
"schedule dispatch" or "unplug work" functions.  In blk, CFQ and BFQ
do these schedules/unplugs in a lot of cases.  What's the right
replacement?  Just doing nothing?

You just use blk_mq_run_hw_queue() or variants thereof to kick off queue
runs.

Hi Jens,
I'm working on this right now.  I have a pair of quick questions about
performance.

In the blk version of bfq, if the in-service bfq_queue happen to have
no more budget when the bfq dispatch function is invoked, then bfq:
returns no request (NULL), immediately expires the in-service
bfq_queue, and schedules a new dispatch.  The third step is taken so
that, if other bfq_queues have requests, then a new in-service
bfq_queue will be selected on the upcoming new dispatch, and a new
request will be provided right away.

My questions are: is this dispatch-schedule step still needed with
blk-mq, to avoid a stall?  If it is not needed to avoid a stall, would
it still be needed to boost throughput, because it would force an
immediate, next dispatch?

Generally that step is only needed if you don't dispatch a request for
that invocation, yet you have requests to dispatch. For that case, you
must ensure that the queues are run at some point in the future. So I'm
inclined to answer yes to your question, though it depends on exactly
how it happens. If you have the queue run in the code, comment it like
that, and we can always revisit.

BTW, bfq-mq survived its first request completion.  I will provide you
with a link to a github branch as soon as bfq-mq seems able to stand
up with a minimal workload.

Congratulations, that's a nice milestone!

-- 
Jens Axboe