Re: [PATCH v3] xen/blkfront: convert to blk-mq APIs

From: Rafal Mielniczuk
Date: Fri Aug 21 2015 - 04:46:51 EST

Next message: Pali RohÃr: "Re: omapdss: Division by zero in kernel"
Previous message: Rameshwar Sahu: "Re: [PATCH] dmaengine: xgene-dma: Fix holding lock while calling tx callback in cleanup path"
In reply to: Bob Liu: "Re: [PATCH v3] xen/blkfront: convert to blk-mq APIs"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On 19/08/15 12:12, Bob Liu wrote:
> Hi Jens & Christoph,
>
> Rafal reported an issue about this patch, that's after this patch no more
> merges happen and the performance dropped if "modprobe null_blk irqmode=2 completion_nsec=1000000",
> but works fine if "modprobe null_blk".
>
> I'm not sure whether it's as expect or not.
> Do you have any suggestions? Thank you!
>
> Here is the test result:
>
> fio --name=test --ioengine=libaio --rw=read --numjobs=8 --iodepth=32 \
> --time_based=1 --runtime=30 --bs=4KB --filename=/dev/xvdb \
> --direct=1 --group_reporting=1 --iodepth_batch=16
>
> ========================================================================
> modprobe null_blk
> ========================================================================
> ------------------------------------------------------------------------
> *no patch* (avgrq-sz = 8.00 avgqu-sz=5.00)
> ------------------------------------------------------------------------
> READ: io=10655MB, aggrb=363694KB/s, minb=363694KB/s, maxb=363694KB/s, mint=30001msec, maxt=30001msec
>
> Disk stats (read/write):
> xvdb: ios=2715852/0, merge=1089/0, ticks=126572/0, in_queue=127456, util=100.00%
>
> ------------------------------------------------------------------------
> *with patch* (avgrq-sz = 8.00 avgqu-sz=8.00)
> ------------------------------------------------------------------------
> READ: io=20655MB, aggrb=705010KB/s, minb=705010KB/s, maxb=705010KB/s, mint=30001msec, maxt=30001msec
>
> Disk stats (read/write):
> xvdb: ios=5274633/0, merge=22/0, ticks=243208/0, in_queue=242908, util=99.98%
>
> ========================================================================
> modprobe null_blk irqmode=2 completion_nsec=1000000
> ========================================================================
> ------------------------------------------------------------------------
> *no patch* (avgrq-sz = 34.00 avgqu-sz=38.00)
> ------------------------------------------------------------------------
> READ: io=10372MB, aggrb=354008KB/s, minb=354008KB/s, maxb=354008KB/s, mint=30003msec, maxt=30003msec
>
> Disk stats (read/write):
> xvdb: ios=621760/0, *merge=1988170/0*, ticks=1136700/0, in_queue=1146020, util=99.76%
>
> ------------------------------------------------------------------------
> *with patch* (avgrq-sz = 8.00 avgqu-sz=28.00)
> ------------------------------------------------------------------------
> READ: io=2876.8MB, aggrb=98187KB/s, minb=98187KB/s, maxb=98187KB/s, mint=30002msec, maxt=30002msec
>
> Disk stats (read/write):
> xvdb: ios=734048/0, merge=0/0, ticks=843584/0, in_queue=843080, util=99.72%
>
> Regards,
> -Bob

Hello,

We got a problem with the lack of merges also when we tested on null_blk device in dom0 directly.
When we enabled multi queue block-layer we got no merges, even when we set the number of submission queues to 1.

If I don't miss anything, that could suggest the problem lays somewhere in the blk-mq layer itself?

Please take a look at the results below:

fio --name=test --ioengine=libaio --rw=read --numjobs=8 --iodepth=32 \
--time_based=1 --runtime=30 --bs=4KB --filename=/dev/nullb0 \
--direct=1 --group_reporting=1

========================================================================
modprobe null_blk irqmode=2 completion_nsec=1000000 queue_mode=1 submit_queues=1
========================================================================
READ: io=13692MB, aggrb=467320KB/s, minb=467320KB/s, maxb=467320KB/s, mint=30002msec, maxt=30002msec

Disk stats (read/write):
nullb0: ios=991026/0, merge=2499524/0, ticks=1846952/0, in_queue=900012, util=100.00%

========================================================================
modprobe null_blk irqmode=2 completion_nsec=1000000 queue_mode=2 submit_queues=1
========================================================================
READ: io=6839.1MB, aggrb=233452KB/s, minb=233452KB/s, maxb=233452KB/s, mint=30002msec, maxt=30002msec

Disk stats (read/write):
nullb0: ios=1743967/0, merge=0/0, ticks=1712900/0, in_queue=1839072, util=100.00%

Thanks,
Rafal

>
> On 07/13/2015 05:55 PM, Bob Liu wrote:
>> Note: This patch is based on original work of Arianna's internship for
>> GNOME's Outreach Program for Women.
>>
>> Only one hardware queue is used now, so there is no performance change.
>>
>> The legacy non-mq code is deleted completely which is the same as other
>> drivers like virtio, mtip, and nvme.
>>
>> Also dropped one unnecessary holding of info->io_lock when calling
>> blk_mq_stop_hw_queues().
>>
>> Changes in v2:
>> - Reorganized blk_mq_queue_rq()
>> - Restored most io_locks in place
>>
>> Change in v3:
>> - Rename blk_mq_queue_rq to blkif_queue_rq
>>
>> Signed-off-by: Arianna Avanzini <avanzini.arianna@xxxxxxxxx>
>> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
>> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
>> Acked-by: Jens Axboe <axboe@xxxxxx>
>> ---
>> drivers/block/xen-blkfront.c | 146 +++++++++++++++++-------------------------
>> 1 file changed, 60 insertions(+), 86 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 6d89ed3..5b45ee5 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -37,6 +37,7 @@
>>
>> #include <linux/interrupt.h>
>> #include <linux/blkdev.h>
>> +#include <linux/blk-mq.h>
>> #include <linux/hdreg.h>
>> #include <linux/cdrom.h>
>> #include <linux/module.h>
>> @@ -148,6 +149,7 @@ struct blkfront_info
>> unsigned int feature_persistent:1;
>> unsigned int max_indirect_segments;
>> int is_ready;
>> + struct blk_mq_tag_set tag_set;
>> };
>>
>> static unsigned int nr_minors;
>> @@ -616,54 +618,41 @@ static inline bool blkif_request_flush_invalid(struct request *req,
>> !(info->feature_flush & REQ_FUA)));
>> }
>>
>> -/*
>> - * do_blkif_request
>> - * read a block; request is in a request queue
>> - */
>> -static void do_blkif_request(struct request_queue *rq)
>> +static int blkif_queue_rq(struct blk_mq_hw_ctx *hctx,
>> + const struct blk_mq_queue_data *qd)
>> {
>> - struct blkfront_info *info = NULL;
>> - struct request *req;
>> - int queued;
>> -
>> - pr_debug("Entered do_blkif_request\n");
>> -
>> - queued = 0;
>> + struct blkfront_info *info = qd->rq->rq_disk->private_data;
>>
>> - while ((req = blk_peek_request(rq)) != NULL) {
>> - info = req->rq_disk->private_data;
>> -
>> - if (RING_FULL(&info->ring))
>> - goto wait;
>> + blk_mq_start_request(qd->rq);
>> + spin_lock_irq(&info->io_lock);
>> + if (RING_FULL(&info->ring))
>> + goto out_busy;
>>
>> - blk_start_request(req);
>> + if (blkif_request_flush_invalid(qd->rq, info))
>> + goto out_err;
>>
>> - if (blkif_request_flush_invalid(req, info)) {
>> - __blk_end_request_all(req, -EOPNOTSUPP);
>> - continue;
>> - }
>> + if (blkif_queue_request(qd->rq))
>> + goto out_busy;
>>
>> - pr_debug("do_blk_req %p: cmd %p, sec %lx, "
>> - "(%u/%u) [%s]\n",
>> - req, req->cmd, (unsigned long)blk_rq_pos(req),
>> - blk_rq_cur_sectors(req), blk_rq_sectors(req),
>> - rq_data_dir(req) ? "write" : "read");
>> -
>> - if (blkif_queue_request(req)) {
>> - blk_requeue_request(rq, req);
>> -wait:
>> - /* Avoid pointless unplugs. */
>> - blk_stop_queue(rq);
>> - break;
>> - }
>> + flush_requests(info);
>> + spin_unlock_irq(&info->io_lock);
>> + return BLK_MQ_RQ_QUEUE_OK;
>>
>> - queued++;
>> - }
>> +out_err:
>> + spin_unlock_irq(&info->io_lock);
>> + return BLK_MQ_RQ_QUEUE_ERROR;
>>
>> - if (queued != 0)
>> - flush_requests(info);
>> +out_busy:
>> + spin_unlock_irq(&info->io_lock);
>> + blk_mq_stop_hw_queue(hctx);
>> + return BLK_MQ_RQ_QUEUE_BUSY;
>> }
>>
>> +static struct blk_mq_ops blkfront_mq_ops = {
>> + .queue_rq = blkif_queue_rq,
>> + .map_queue = blk_mq_map_queue,
>> +};
>> +
>> static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
>> unsigned int physical_sector_size,
>> unsigned int segments)
>> @@ -671,9 +660,22 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
>> struct request_queue *rq;
>> struct blkfront_info *info = gd->private_data;
>>
>> - rq = blk_init_queue(do_blkif_request, &info->io_lock);
>> - if (rq == NULL)
>> + memset(&info->tag_set, 0, sizeof(info->tag_set));
>> + info->tag_set.ops = &blkfront_mq_ops;
>> + info->tag_set.nr_hw_queues = 1;
>> + info->tag_set.queue_depth = BLK_RING_SIZE(info);
>> + info->tag_set.numa_node = NUMA_NO_NODE;
>> + info->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
>> + info->tag_set.cmd_size = 0;
>> + info->tag_set.driver_data = info;
>> +
>> + if (blk_mq_alloc_tag_set(&info->tag_set))
>> return -1;
>> + rq = blk_mq_init_queue(&info->tag_set);
>> + if (IS_ERR(rq)) {
>> + blk_mq_free_tag_set(&info->tag_set);
>> + return -1;
>> + }
>>
>> queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);
>>
>> @@ -901,19 +903,15 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
>> static void xlvbd_release_gendisk(struct blkfront_info *info)
>> {
>> unsigned int minor, nr_minors;
>> - unsigned long flags;
>>
>> if (info->rq == NULL)
>> return;
>>
>> - spin_lock_irqsave(&info->io_lock, flags);
>> -
>> /* No more blkif_request(). */
>> - blk_stop_queue(info->rq);
>> + blk_mq_stop_hw_queues(info->rq);
>>
>> /* No more gnttab callback work. */
>> gnttab_cancel_free_callback(&info->callback);
>> - spin_unlock_irqrestore(&info->io_lock, flags);
>>
>> /* Flush gnttab callback work. Must be done with no locks held. */
>> flush_work(&info->work);
>> @@ -925,20 +923,18 @@ static void xlvbd_release_gendisk(struct blkfront_info *info)
>> xlbd_release_minors(minor, nr_minors);
>>
>> blk_cleanup_queue(info->rq);
>> + blk_mq_free_tag_set(&info->tag_set);
>> info->rq = NULL;
>>
>> put_disk(info->gd);
>> info->gd = NULL;
>> }
>>
>> +/* Must be called with io_lock holded */
>> static void kick_pending_request_queues(struct blkfront_info *info)
>> {
>> - if (!RING_FULL(&info->ring)) {
>> - /* Re-enable calldowns. */
>> - blk_start_queue(info->rq);
>> - /* Kick things off immediately. */
>> - do_blkif_request(info->rq);
>> - }
>> + if (!RING_FULL(&info->ring))
>> + blk_mq_start_stopped_hw_queues(info->rq, true);
>> }
>>
>> static void blkif_restart_queue(struct work_struct *work)
>> @@ -963,7 +959,7 @@ static void blkif_free(struct blkfront_info *info, int suspend)
>> BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
>> /* No more blkif_request(). */
>> if (info->rq)
>> - blk_stop_queue(info->rq);
>> + blk_mq_stop_hw_queues(info->rq);
>>
>> /* Remove all persistent grants */
>> if (!list_empty(&info->grants)) {
>> @@ -1144,7 +1140,6 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>> RING_IDX i, rp;
>> unsigned long flags;
>> struct blkfront_info *info = (struct blkfront_info *)dev_id;
>> - int error;
>>
>> spin_lock_irqsave(&info->io_lock, flags);
>>
>> @@ -1185,37 +1180,37 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>> continue;
>> }
>>
>> - error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
>> + req->errors = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
>> switch (bret->operation) {
>> case BLKIF_OP_DISCARD:
>> if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
>> struct request_queue *rq = info->rq;
>> printk(KERN_WARNING "blkfront: %s: %s op failed\n",
>> info->gd->disk_name, op_name(bret->operation));
>> - error = -EOPNOTSUPP;
>> + req->errors = -EOPNOTSUPP;
>> info->feature_discard = 0;
>> info->feature_secdiscard = 0;
>> queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
>> queue_flag_clear(QUEUE_FLAG_SECDISCARD, rq);
>> }
>> - __blk_end_request_all(req, error);
>> + blk_mq_complete_request(req);
>> break;
>> case BLKIF_OP_FLUSH_DISKCACHE:
>> case BLKIF_OP_WRITE_BARRIER:
>> if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
>> printk(KERN_WARNING "blkfront: %s: %s op failed\n",
>> info->gd->disk_name, op_name(bret->operation));
>> - error = -EOPNOTSUPP;
>> + req->errors = -EOPNOTSUPP;
>> }
>> if (unlikely(bret->status == BLKIF_RSP_ERROR &&
>> info->shadow[id].req.u.rw.nr_segments == 0)) {
>> printk(KERN_WARNING "blkfront: %s: empty %s op failed\n",
>> info->gd->disk_name, op_name(bret->operation));
>> - error = -EOPNOTSUPP;
>> + req->errors = -EOPNOTSUPP;
>> }
>> - if (unlikely(error)) {
>> - if (error == -EOPNOTSUPP)
>> - error = 0;
>> + if (unlikely(req->errors)) {
>> + if (req->errors == -EOPNOTSUPP)
>> + req->errors = 0;
>> info->feature_flush = 0;
>> xlvbd_flush(info);
>> }
>> @@ -1226,7 +1221,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
>> dev_dbg(&info->xbdev->dev, "Bad return from blkdev data "
>> "request: %x\n", bret->status);
>>
>> - __blk_end_request_all(req, error);
>> + blk_mq_complete_request(req);
>> break;
>> default:
>> BUG();
>> @@ -1555,28 +1550,6 @@ static int blkif_recover(struct blkfront_info *info)
>>
>> kfree(copy);
>>
>> - /*
>> - * Empty the queue, this is important because we might have
>> - * requests in the queue with more segments than what we
>> - * can handle now.
>> - */
>> - spin_lock_irq(&info->io_lock);
>> - while ((req = blk_fetch_request(info->rq)) != NULL) {
>> - if (req->cmd_flags &
>> - (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
>> - list_add(&req->queuelist, &requests);
>> - continue;
>> - }
>> - merge_bio.head = req->bio;
>> - merge_bio.tail = req->biotail;
>> - bio_list_merge(&bio_list, &merge_bio);
>> - req->bio = NULL;
>> - if (req->cmd_flags & (REQ_FLUSH | REQ_FUA))
>> - pr_alert("diskcache flush request found!\n");
>> - __blk_end_request_all(req, 0);
>> - }
>> - spin_unlock_irq(&info->io_lock);
>> -
>> xenbus_switch_state(info->xbdev, XenbusStateConnected);
>>
>> spin_lock_irq(&info->io_lock);
>> @@ -1591,9 +1564,10 @@ static int blkif_recover(struct blkfront_info *info)
>> /* Requeue pending requests (flush or discard) */
>> list_del_init(&req->queuelist);
>> BUG_ON(req->nr_phys_segments > segs);
>> - blk_requeue_request(info->rq, req);
>> + blk_mq_requeue_request(req);
>> }
>> spin_unlock_irq(&info->io_lock);
>> + blk_mq_kick_requeue_list(info->rq);
>>
>> while ((bio = bio_list_pop(&bio_list)) != NULL) {
>> /* Traverse the list of pending bios and re-queue them */
>>

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Next message: Pali RohÃr: "Re: omapdss: Division by zero in kernel"
Previous message: Rameshwar Sahu: "Re: [PATCH] dmaengine: xgene-dma: Fix holding lock while calling tx callback in cleanup path"
In reply to: Bob Liu: "Re: [PATCH v3] xen/blkfront: convert to blk-mq APIs"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]