On Sat, Apr 16, 2022 at 07:49:13AM +0200, Christoph Hellwig wrote: > On Fri, Apr 15, 2022 at 07:00:37PM +0800, Ming Lei wrote: > > On Fri, Apr 15, 2022 at 07:18:44AM +0200, Christoph Hellwig wrote: > > > On Fri, Apr 15, 2022 at 11:47:03AM +0800, Ming Lei wrote: > > > > + /* make sure the bio is issued before polling */ > > > > + if (bio.bi_opf & REQ_POLLED) > > > > + blk_flush_plug(current->plug, false); > > > > > > I still think the core code should handle this. Without that we'd need > > > to export the blk_flush_plug for anything that would want to poll bios > > > from modules, in addition to it generally being a mess. See a proposed > > > > So far there isn't such usage yet. dm calls bio_poll() in ->iopoll(), > > and its caller(io_uring) will finish the plug. > > Yes. But not doing this automatically also means you keep easily > forgetting callsites. For example iomap still does not flush the plug > in your patch. It is reasonable for flush user(usually submission) to be responsible for finishing/flushing plug. iomap is one good example to show this point, since it does flush the plug before call bio_poll(), see __iomap_dio_rw(). > > > > patch for that below. I'd also split the flush aspect from the poll > > > aspect into two patches. > > > > > > > + if (bio.bi_opf & REQ_POLLED) > > > > + bio_poll(&bio, NULL, 0); > > > > + else > > > > blk_io_schedule(); > > > > > > Instead of this duplicate logic everywhere I'd just make bio_boll > > > call blk_io_schedule for the !REQ_POLLED case and simplify all the > > > callers. > > > > bio_poll() may be called with rcu read lock held, so I'd suggest to > > not mix the two together. > > Ok, makes sense. > > > > > > > > + if (dio->submit.poll_bio && > > > > + (dio->submit.poll_bio->bi_opf & > > > > + REQ_POLLED)) > > > > > > This indentation looks awfull,normal would be: > > > > > > if (dio->submit.poll_bio && > > > (dio->submit.poll_bio->bi_opf & REQ_POLLED)) > > > > That follows the indentation style of fs/iomap/direct-io.c for break in > > 'if'. > > It doesn't. Just look at the conditional you replaced for example :) OK, I will change to your style. > > > > + /* > > > + * We can't plug for synchronously polled submissions, otherwise > > > + * bio->bi_cookie won't be set directly after submission, which is the > > > + * indicator used by the submitter to check if a bio needs polling. > > > + */ > > > + if (plug && > > > + (rq->bio->bi_opf & (REQ_POLLED | REQ_NOWAIT)) != REQ_POLLED) > > > blk_add_rq_to_plug(plug, rq); > > > else if ((rq->rq_flags & RQF_ELV) || > > > (rq->mq_hctx->dispatch_busy && > > > > It is nothing to do with REQ_NOWAIT. sync polled dio can be marked as > > REQ_NOWAIT by userspace too. If '--nowait=1' is added in the fio > > reproducer, io timeout is triggered too. > > True. So I guess we'll need a new flag to distinguish the cases. If there will be more such kind of poll usage in kernel, I think it is fine to add the flag, but so far all the three aren't used very often. Thanks, Ming
