On Wed, May 21, 2014 at 1:36 PM, Christoph Hellwig <hch@xxxxxx> wrote: > On Wed, May 21, 2014 at 01:16:14PM +0800, Ming Lei wrote: >> I am wondering if virtio-blk is trivial block driver, :-) > > It's about as simple as it gets. > >> > The scsi-mq work that I plant to submit for the next merge window is >> > the prime example. >> >> It depends if one scsi-mq req has to requeue itself with rq->requeue_work >> inside its own .softirq_done_fn. If yes, we can't put call_single_data >> and requeue_work into one union simply. From you last scsi-mq post, >> looks the request may do that if I understand correctly. > > Requeueing a request from the completion handler is indeed what we'll > need with various more complete drivers. At least for scsi, the current scsi_cmnd->abort_work(reusing) should be enough for requeing the command. For other drivers, maybe they can make use of something like scsi_cmnd->abort_work too. > >> I think the patch is clean and simple, with documenting the special >> conflict case clearly too. > > While I can't say anything against the fact that it fixes the issue > it's neither clean nor simple. It just uses q->flush_rq's own work_struct for requeuing itself, that is it. I'd like to see a cleaner/simpler solution without wasting space and extra complexity. > >> Follows current ideas: >> 1), this patch with scsi-mq sharing abort_work together? >> 2), move requeue_work out of the union inside request >> 3), spin_lock_irqsave(&ctx->lock) everywhere and requeue >> request directly to ctx without using work > > I think Jens very much wanted to avoid irq disabling in the I/O path > if possible. If we have a separate requeue list with it's separate > lock we can avoid that unless we actually have to take requests of > that requeue list. I can look into that implementation. I am wondering if you can keep requests in order per blk-mq ctx since you introduce another list. Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html