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()).
-- Steve
