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Tsirkin" To: Suwan Kim Subject: Re: [PATCH v3 1/2] virtio-blk: support polling I/O Message-ID: <20220324103056-mutt-send-email-mst@kernel.org> References: <20220324140450.33148-1-suwan.kim027@gmail.com> <20220324140450.33148-2-suwan.kim027@gmail.com> MIME-Version: 1.0 In-Reply-To: <20220324140450.33148-2-suwan.kim027@gmail.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: mgurtovoy@nvidia.com, kernel test robot , virtualization@lists.linux-foundation.org, linux-block@vger.kernel.org, stefanha@redhat.com, pbonzini@redhat.com X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Thu, Mar 24, 2022 at 11:04:49PM +0900, Suwan Kim wrote: > This patch supports polling I/O via virtio-blk driver. Polling > feature is enabled by module parameter "num_poll_queues" and it > sets dedicated polling queues for virtio-blk. This patch improves > the polling I/O throughput and latency. > > The virtio-blk driver doesn't not have a poll function and a poll > queue and it has been operating in interrupt driven method even if > the polling function is called in the upper layer. > > virtio-blk polling is implemented upon 'batched completion' of block > layer. virtblk_poll() queues completed request to io_comp_batch->req_list > and later, virtblk_complete_batch() calls unmap function and ends > the requests in batch. > > virtio-blk reads the number of poll queues from module parameter > "num_poll_queues". If VM sets queue parameter as below, > ("num-queues=N" [QEMU property], "num_poll_queues=M" [module parameter]) > It allocates N virtqueues to virtio_blk->vqs[N] and it uses [0..(N-M-1)] > as default queues and [(N-M)..(N-1)] as poll queues. Unlike the default > queues, the poll queues have no callback function. > > Regarding HW-SW queue mapping, the default queue mapping uses the > existing method that condsiders MSI irq vector. But the poll queue > doesn't have an irq, so it uses the regular blk-mq cpu mapping. > > For verifying the improvement, I did Fio polling I/O performance test > with io_uring engine with the options below. > (io_uring, hipri, randread, direct=1, bs=512, iodepth=64 numjobs=N) > I set 4 vcpu and 4 virtio-blk queues - 2 default queues and 2 poll > queues for VM. > > As a result, IOPS and average latency improved about 10%. > > Test result: > > - Fio io_uring poll without virtio-blk poll support > -- numjobs=1 : IOPS = 339K, avg latency = 188.33us > -- numjobs=2 : IOPS = 367K, avg latency = 347.33us > -- numjobs=4 : IOPS = 383K, avg latency = 682.06us > > - Fio io_uring poll with virtio-blk poll support > -- numjobs=1 : IOPS = 380K, avg latency = 167.87us > -- numjobs=2 : IOPS = 409K, avg latency = 312.6us > -- numjobs=4 : IOPS = 413K, avg latency = 619.72us > > Reported-by: kernel test robot > Signed-off-by: Suwan Kim > --- > drivers/block/virtio_blk.c | 101 +++++++++++++++++++++++++++++++++++-- > 1 file changed, 97 insertions(+), 4 deletions(-) > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > index 8c415be86732..3d16f8b753e7 100644 > --- a/drivers/block/virtio_blk.c > +++ b/drivers/block/virtio_blk.c > @@ -37,6 +37,10 @@ MODULE_PARM_DESC(num_request_queues, > "0 for no limit. " > "Values > nr_cpu_ids truncated to nr_cpu_ids."); > > +static unsigned int num_poll_queues; > +module_param(num_poll_queues, uint, 0644); > +MODULE_PARM_DESC(num_poll_queues, "The number of dedicated virtqueues for polling I/O"); > + > static int major; > static DEFINE_IDA(vd_index_ida); > Is there some way to make it work reasonably without need to set module parameters? I don't see any other devices with a num_poll_queues parameter - how do they handle this? > @@ -81,6 +85,7 @@ struct virtio_blk { > > /* num of vqs */ > int num_vqs; > + int io_queues[HCTX_MAX_TYPES]; > struct virtio_blk_vq *vqs; > }; > > @@ -548,6 +553,7 @@ static int init_vq(struct virtio_blk *vblk) > const char **names; > struct virtqueue **vqs; > unsigned short num_vqs; > + unsigned int num_poll_vqs; > struct virtio_device *vdev = vblk->vdev; > struct irq_affinity desc = { 0, }; > > @@ -556,6 +562,7 @@ static int init_vq(struct virtio_blk *vblk) > &num_vqs); > if (err) > num_vqs = 1; > + > if (!err && !num_vqs) { > dev_err(&vdev->dev, "MQ advertised but zero queues reported\n"); > return -EINVAL; > @@ -565,6 +572,13 @@ static int init_vq(struct virtio_blk *vblk) > min_not_zero(num_request_queues, nr_cpu_ids), > num_vqs); > > + num_poll_vqs = min_t(unsigned int, num_poll_queues, num_vqs - 1); > + > + memset(vblk->io_queues, 0, sizeof(int) * HCTX_MAX_TYPES); > + vblk->io_queues[HCTX_TYPE_DEFAULT] = num_vqs - num_poll_vqs; > + vblk->io_queues[HCTX_TYPE_READ] = 0; > + vblk->io_queues[HCTX_TYPE_POLL] = num_poll_vqs; > + > vblk->vqs = kmalloc_array(num_vqs, sizeof(*vblk->vqs), GFP_KERNEL); > if (!vblk->vqs) > return -ENOMEM; > @@ -578,8 +592,13 @@ static int init_vq(struct virtio_blk *vblk) > } > > for (i = 0; i < num_vqs; i++) { > - callbacks[i] = virtblk_done; > - snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i); > + if (i < num_vqs - num_poll_vqs) { > + callbacks[i] = virtblk_done; > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req.%d", i); > + } else { > + callbacks[i] = NULL; > + snprintf(vblk->vqs[i].name, VQ_NAME_LEN, "req_poll.%d", i); > + } > names[i] = vblk->vqs[i].name; > } > > @@ -728,16 +747,87 @@ static const struct attribute_group *virtblk_attr_groups[] = { > static int virtblk_map_queues(struct blk_mq_tag_set *set) > { > struct virtio_blk *vblk = set->driver_data; > + int i, qoff; > + > + for (i = 0, qoff = 0; i < set->nr_maps; i++) { > + struct blk_mq_queue_map *map = &set->map[i]; > + > + map->nr_queues = vblk->io_queues[i]; > + map->queue_offset = qoff; > + qoff += map->nr_queues; > + > + if (map->nr_queues == 0) > + continue; > + > + /* > + * Regular queues have interrupts and hence CPU affinity is > + * defined by the core virtio code, but polling queues have > + * no interrupts so we let the block layer assign CPU affinity. > + */ > + if (i == HCTX_TYPE_DEFAULT) > + blk_mq_virtio_map_queues(&set->map[i], vblk->vdev, 0); > + else > + blk_mq_map_queues(&set->map[i]); > + } > + > + return 0; > +} > + > +static void virtblk_complete_batch(struct io_comp_batch *iob) > +{ > + struct request *req; > + struct virtblk_req *vbr; > > - return blk_mq_virtio_map_queues(&set->map[HCTX_TYPE_DEFAULT], > - vblk->vdev, 0); > + rq_list_for_each(&iob->req_list, req) { > + vbr = blk_mq_rq_to_pdu(req); > + virtblk_unmap_data(req, vbr); > + 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_vq *vq = hctx->driver_data; > + struct virtblk_req *vbr; > + unsigned long flags; > + unsigned int len; > + int found = 0; > + > + spin_lock_irqsave(&vq->lock, flags); > + > + while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) { > + struct request *req = blk_mq_rq_from_pdu(vbr); > + > + found++; > + if (!blk_mq_add_to_batch(req, iob, vbr->status, > + virtblk_complete_batch)) > + blk_mq_complete_request(req); > + } > + > + spin_unlock_irqrestore(&vq->lock, flags); > + > + return found; > +} > + > +static int virtblk_init_hctx(struct blk_mq_hw_ctx *hctx, void *data, > + unsigned int hctx_idx) > +{ > + struct virtio_blk *vblk = data; > + struct virtio_blk_vq *vq = &vblk->vqs[hctx_idx]; > + > + WARN_ON(vblk->tag_set.tags[hctx_idx] != hctx->tags); > + hctx->driver_data = vq; > + return 0; > } > > static const struct blk_mq_ops virtio_mq_ops = { > .queue_rq = virtio_queue_rq, > .commit_rqs = virtio_commit_rqs, > + .init_hctx = virtblk_init_hctx, > .complete = virtblk_request_done, > .map_queues = virtblk_map_queues, > + .poll = virtblk_poll, > }; > > static unsigned int virtblk_queue_depth; > @@ -816,6 +906,9 @@ static int virtblk_probe(struct virtio_device *vdev) > sizeof(struct scatterlist) * VIRTIO_BLK_INLINE_SG_CNT; > vblk->tag_set.driver_data = vblk; > vblk->tag_set.nr_hw_queues = vblk->num_vqs; > + vblk->tag_set.nr_maps = 1; > + if (vblk->io_queues[HCTX_TYPE_POLL]) > + vblk->tag_set.nr_maps = 3; > > err = blk_mq_alloc_tag_set(&vblk->tag_set); > if (err) > -- > 2.26.3 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization