Re: [PATCH v4 4/6] blk-mq: Introduce blk_mq_delay_run_hw_queue()

[Jens Axboe <axboe@kernel.dk>]

On 04/10/2017 01:12 AM, Christoph Hellwig wrote:
>> +	if (msecs == 0)
>> +		kblockd_schedule_work_on(blk_mq_hctx_next_cpu(hctx),
>> +					 &hctx->run_work);
>> +	else
>> +		kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
>> +						 &hctx->delayed_run_work,
>> +						 msecs_to_jiffies(msecs));
>> +}
> 
> I'd rather make run_work a delayed_work (again) and use
> kblockd_schedule_delayed_work_on with a timeout of zero for the immediate
> run case instead of having two competing work structs.

Yeah that's a good point, it'd have to be an incremental patch at this
point though. Also note that blk_mq_stop_hw_queue() isn't currently
canceling the new ->delayed_run_work, that looks like a bug.

And looking at it, right now we have 3 (three!) work items in the
hardware queue. The two delayed items differ in that one of them only
runs the queue it was previously stopped, that's it. The non-delayed one
is identical to the non stopped checking delayed variant.

I'll send out a patch.

-- 
Jens Axboe