Michael S. Tsirkin
2023-Jun-09 09:42 UTC
[PATCH v2] Revert "virtio-blk: support completion batching for the IRQ path"
On Fri, Jun 09, 2023 at 09:34:40AM +0000, Roberts, Martin wrote:> I think, at some point, vbr->status, got changed to virtblk_vbr_status(vbr). > If I use the version of virtblk_poll() from the patch, but substitute virtblk_vbr_status(vbr), then it (patched 6.3.3) compiles OK.Hmm v2 does not have vbr->status anymore. Are you referring to v1?> Note, my setup never causes virtblk_poll() to be called, so its influence on the issue is unknown - but maybe it also shouldn't be running in batch mode. > > With the patch, I've not (yet) managed to hang it - I will let it run a bit longer. > MartinWant to post the patch that works for you?> -----Original Message----- > From: Michael S. Tsirkin <mst at redhat.com> > Sent: Friday, June 9, 2023 8:27 AM > To: linux-kernel at vger.kernel.org > Cc: lkp <lkp at intel.com>; Suwan Kim <suwan.kim027 at gmail.com>; Roberts, Martin <martin.roberts at intel.com>; Jason Wang <jasowang at redhat.com>; Paolo Bonzini <pbonzini at redhat.com>; Stefan Hajnoczi <stefanha at redhat.com>; Xuan Zhuo <xuanzhuo at linux.alibaba.com>; Jens Axboe <axboe at kernel.dk>; virtualization at lists.linux-foundation.org; linux-block at vger.kernel.org > Subject: [PATCH v2] Revert "virtio-blk: support completion batching for the IRQ path" > > This reverts commit 07b679f70d73483930e8d3c293942416d9cd5c13. > > This change appears to have broken things... > We now see applications hanging during disk accesses. > e.g. > multi-port virtio-blk device running in h/w (FPGA) > Host running a simple 'fio' test. > [global] > thread=1 > direct=1 > ioengine=libaio > norandommap=1 > group_reporting=1 > bs=4K > rw=read > iodepth=128 > runtime=1 > numjobs=4 > time_based > [job0] > filename=/dev/vda > [job1] > filename=/dev/vdb > [job2] > filename=/dev/vdc > ... > [job15] > filename=/dev/vdp > > i.e. 16 disks; 4 queues per disk; simple burst of 4KB reads > This is repeatedly run in a loop. > > After a few, normally <10 seconds, fio hangs. > With 64 queues (16 disks), failure occurs within a few seconds; with 8 queues (2 disks) it may take ~hour before hanging. > Last message: > fio-3.19 > Starting 8 threads > Jobs: 1 (f=1): [_(7),R(1)][68.3%][eta 03h:11m:06s] > I think this means at the end of the run 1 queue was left incomplete. > > 'diskstats' (run while fio is hung) shows no outstanding transactions. > e.g. > $ cat /proc/diskstats > ... > 252 0 vda 1843140071 0 14745120568 712568645 0 0 0 0 0 3117947 712568645 0 0 0 0 0 0 > 252 16 vdb 1816291511 0 14530332088 704905623 0 0 0 0 0 3117711 704905623 0 0 0 0 0 0 > ... > > Other stats (in the h/w, and added to the virtio-blk driver ([a]virtio_queue_rq(), [b]virtblk_handle_req(), [c]virtblk_request_done()) all agree, and show every request had a completion, and that virtblk_request_done() never gets called. > e.g. > PF= 0 vq=0 1 2 3 > [a]request_count - 839416590 813148916 105586179 84988123 > [b]completion1_count - 839416590 813148916 105586179 84988123 > [c]completion2_count - 0 0 0 0 > > PF= 1 vq=0 1 2 3 > [a]request_count - 823335887 812516140 104582672 75856549 > [b]completion1_count - 823335887 812516140 104582672 75856549 > [c]completion2_count - 0 0 0 0 > > i.e. the issue is after the virtio-blk driver. > > This change was introduced in kernel 6.3.0. > I am seeing this using 6.3.3. > If I run with an earlier kernel (5.15), it does not occur. > If I make a simple patch to the 6.3.3 virtio-blk driver, to skip the blk_mq_add_to_batch()call, it does not fail. > e.g. > kernel 5.15 - this is OK > virtio_blk.c,virtblk_done() [irq handler] > if (likely(!blk_should_fake_timeout(req->q))) { > blk_mq_complete_request(req); > } > > kernel 6.3.3 - this fails > virtio_blk.c,virtblk_handle_req() [irq handler] > if (likely(!blk_should_fake_timeout(req->q))) { > if (!blk_mq_complete_request_remote(req)) { > if (!blk_mq_add_to_batch(req, iob, virtblk_vbr_status(vbr), virtblk_complete_batch)) { > virtblk_request_done(req); //this never gets called... so blk_mq_add_to_batch() must always succeed > } > } > } > > If I do, kernel 6.3.3 - this is OK > virtio_blk.c,virtblk_handle_req() [irq handler] > if (likely(!blk_should_fake_timeout(req->q))) { > if (!blk_mq_complete_request_remote(req)) { > virtblk_request_done(req); //force this here... > if (!blk_mq_add_to_batch(req, iob, virtblk_vbr_status(vbr), virtblk_complete_batch)) { > virtblk_request_done(req); //this never gets called... so blk_mq_add_to_batch() must always succeed > } > } > } > > Perhaps you might like to fix/test/revert this change... > Martin > > Reported-by: kernel test robot <lkp at intel.com> > Closes: https://lore.kernel.org/oe-kbuild-all/202306090826.C1fZmdMe-lkp at intel.com/ > Cc: Suwan Kim <suwan.kim027 at gmail.com> > Reported-by: "Roberts, Martin" <martin.roberts at intel.com> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com> > --- > > Since v1: > fix build error > > Still completely untested as I'm traveling. > Martin, Suwan, could you please test and report? > Suwan if you have a better revert in mind pls post and > I will be happy to drop this. > > Thanks! > > > drivers/block/virtio_blk.c | 82 +++++++++++++++++--------------------- > 1 file changed, 37 insertions(+), 45 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 2b918e28acaa..b47358da92a2 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -348,63 +348,33 @@ static inline void virtblk_request_done(struct request *req) > blk_mq_end_request(req, status); > } > > -static void virtblk_complete_batch(struct io_comp_batch *iob) > -{ > - struct request *req; > - > - rq_list_for_each(&iob->req_list, req) { > - virtblk_unmap_data(req, blk_mq_rq_to_pdu(req)); > - virtblk_cleanup_cmd(req); > - } > - blk_mq_end_request_batch(iob); > -} > - > -static int virtblk_handle_req(struct virtio_blk_vq *vq, > - struct io_comp_batch *iob) > -{ > - struct virtblk_req *vbr; > - int req_done = 0; > - unsigned int len; > - > - while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) { > - struct request *req = blk_mq_rq_from_pdu(vbr); > - > - if (likely(!blk_should_fake_timeout(req->q)) && > - !blk_mq_complete_request_remote(req) && > - !blk_mq_add_to_batch(req, iob, virtblk_vbr_status(vbr), > - virtblk_complete_batch)) > - virtblk_request_done(req); > - req_done++; > - } > - > - return req_done; > -} > - > static void virtblk_done(struct virtqueue *vq) > { > struct virtio_blk *vblk = vq->vdev->priv; > - struct virtio_blk_vq *vblk_vq = &vblk->vqs[vq->index]; > - int req_done = 0; > + bool req_done = false; > + int qid = vq->index; > + struct virtblk_req *vbr; > unsigned long flags; > - DEFINE_IO_COMP_BATCH(iob); > + unsigned int len; > > - spin_lock_irqsave(&vblk_vq->lock, flags); > + spin_lock_irqsave(&vblk->vqs[qid].lock, flags); > do { > virtqueue_disable_cb(vq); > - req_done += virtblk_handle_req(vblk_vq, &iob); > + while ((vbr = virtqueue_get_buf(vblk->vqs[qid].vq, &len)) != NULL) { > + struct request *req = blk_mq_rq_from_pdu(vbr); > > + if (likely(!blk_should_fake_timeout(req->q))) > + blk_mq_complete_request(req); > + req_done = true; > + } > if (unlikely(virtqueue_is_broken(vq))) > break; > } while (!virtqueue_enable_cb(vq)); > > - if (req_done) { > - if (!rq_list_empty(iob.req_list)) > - iob.complete(&iob); > - > - /* In case queue is stopped waiting for more buffers. */ > + /* In case queue is stopped waiting for more buffers. */ > + if (req_done) > blk_mq_start_stopped_hw_queues(vblk->disk->queue, true); > - } > - spin_unlock_irqrestore(&vblk_vq->lock, flags); > + spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); > } > > static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx) > @@ -1283,15 +1253,37 @@ static void virtblk_map_queues(struct blk_mq_tag_set *set) > } > } > > +static void virtblk_complete_batch(struct io_comp_batch *iob) > +{ > + struct request *req; > + > + rq_list_for_each(&iob->req_list, req) { > + virtblk_unmap_data(req, blk_mq_rq_to_pdu(req)); > + virtblk_cleanup_cmd(req); > + } > + blk_mq_end_request_batch(iob); > +} > + > static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob) > { > struct virtio_blk *vblk = hctx->queue->queuedata; > struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx); > + struct virtblk_req *vbr; > unsigned long flags; > + unsigned int len; > int found = 0; > > spin_lock_irqsave(&vq->lock, flags); > - found = virtblk_handle_req(vq, iob); > + > + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) { > + struct request *req = blk_mq_rq_from_pdu(vbr); > + > + found++; > + if (!blk_mq_complete_request_remote(req) && > + !blk_mq_add_to_batch(req, iob, virtblk_vbr_status(vbr), > + virtblk_complete_batch)) > + virtblk_request_done(req); > + } > > if (found) > blk_mq_start_stopped_hw_queues(vblk->disk->queue, true); > -- > MST