On 6/28/18 1:52 PM, Steven Rostedt wrote:
> On Thu, 28 Jun 2018 09:27:08 +0200
> Johannes Thumshirn <jthumshirn@xxxxxxx> wrote:
>
>> Hi Ming,
>>
>> On Thu, Jun 28, 2018 at 11:19:16AM +0800, Ming Lei wrote:
>>> + list_for_each_entry(rq, list, queuelist) {
>>> BUG_ON(rq->mq_ctx != ctx);
>>> - list_del_init(&rq->queuelist);
>>> - __blk_mq_insert_req_list(hctx, rq, false);
>>> + trace_block_rq_insert(hctx->queue, rq);
>>> }
>>
>> I wonder if we really need the above loop unconditionally. It does
>> some BUG_ON() sanity checking (which I hate but it was already there
>> so not your problem) and tracing of the request insertion.
>>
>> So can we maybe only run this loop if tracing is enabled? Not sure if
>> this is possible though. Maybe Steven (Cced) can help here.
>
> Yes:
>
> if (trace_block_rq_insert_enabled()) {
> list_for_each_entry(rq, list, queuelist) {
> BUG_ON(rq->mq_ctx != ctx);
> list_del_init(&rq->queuelist);
> __blk_mq_insert_req_list(hctx, rq, false);
> trace_block_rq_insert(hctx->queue, rq);
> }
> }
>
> This will only call the loop if the trace event "block_rq_insert" has
> been activated. It also uses the jump label infrastructure, so that if
> statement is a non-conditional branch (static_key_false()).
This works for both ftrace and blktrace?
--
Jens Axboe
