linux-kernel - Re: [PATCHSET v2 block/for-5.8] iocost: improve use

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Date:   Mon, 13 Apr 2020 21:49:12 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        cgroups@...r.kernel.org, newella@...com, josef@...icpanda.com,
        ming.lei@...hat.com, bvanassche@....org
Subject: Re: [PATCHSET v2 block/for-5.8] iocost: improve use_delay and latency
 target handling

On 13/04/2020 20:08, Tejun Heo wrote:
> On Mon, Apr 13, 2020 at 08:00:29PM +0300, Pavel Begunkov wrote:
>> On 13/04/2020 19:56, Pavel Begunkov wrote:
>>> On 13/04/2020 19:27, Tejun Heo wrote:
>>>> Changes from v1[1]
>>>>
>>>> * Dropped 0002-block-add-request-io_data_len.patch and updated to use
>>>>   rq->stats_sectors instead as suggested by Pavel Begunkov.
>>>
>>> rq->stats_sectors is set only when there is QUEUE_FLAG_STATS, see
>>> blk_mq_start_request(). I don't see blk-iocost requiring it. Did I miss something?
>>
>> And there is no reason to not initialise it unconditionally.
> 
> The updated patch turns on accounting when iocost is enabled on a queue.

Great. FWIW, if you don't really need accounting, it'd be IMHO more robust and
with less overhead just to do this ->stats_sectors assignment unconditionally.

> 
>   @@ -2267,6 +2295,7 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
>    	spin_lock_irq(&ioc->lock);
>  
>    	if (enable) {
>   +		blk_stat_enable_accounting(ioc->rqos.q);
>    		blk_queue_flag_set(QUEUE_FLAG_RQ_ALLOC_TIME, ioc->rqos.q);
>    		ioc->enabled = true;
>    	} else {
> 
> Thanks.
> 

-- 
Pavel Begunkov