Skip to contentSkip to conversation

Revert "virtio-blk: support completion batching for the IRQ path"

PATCH Superseded Michael S. Tsirkin 2 participants 3 messages Jun 8, 2023 – Jun 9, 2023

Subsystems (3)
Block layer virtio core virtio block and SCSI drivers

v1 of 2 Superseded Latest is v2 →

lore
Share & tools
lore

Michael S. Tsirkin

author maintainer
#0 lore raw

PATCH 1/1 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 "Roberts, Martin" <[email protected]>
Signed-off-by Michael S. Tsirkin <[email protected]>

---

Completely untested.
Martin can you pls test and report whether this fixes the problem? Thanks!

 drivers/block/virtio_blk.c | 82 +++++++++++++++++---------------------
 1 file changed, 37 insertions(+), 45 deletions(-)
drivers/block/virtio_blk.c +37 -45
index 2b918e28acaa..c1e65b4d8071 100644
@@ -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, vbr->status,
+						virtblk_complete_batch))
+			virtblk_request_done(req);
+	}
 
 	if (found)
 		blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
Signature · 6 lines
MST

_______________________________________________
Virtualization mailing list
[email protected]
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
build bot
#1 lore raw
kernel test robot noticed the following build errors:

Hi Michael,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on linus/master v6.4-rc5 next-20230608] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Michael-S-Tsirkin/Revert-virtio-blk-support-completion-batching-for-the-IRQ-path/20230609-054840
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/9443f7273fbba6e62f89e54cbb2a70d2c93ed8e9.1686260774.git.mst%40redhat.com
patch subject: [PATCH] Revert "virtio-blk: support completion batching for the IRQ path"
config: s390-randconfig-r014-20230608 (https://download.01.org/0day-ci/archive/20230609/[email protected]/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project.git 4a5ac14ee968ff0ad5d2cc1ffa0299048db4c88a)

reproduce (this is a W=1 build):
mkdir -p ~/bin
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
# install s390 cross compiling tool for clang build
# apt-get install binutils-s390x-linux-gnu
git remote add axboe-block https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
git fetch axboe-block for-next
git checkout axboe-block/for-next
b4 shazam https://lore.kernel.org/r/9443f7273fbba6e62f89e54cbb2a70d2c93ed8e9.1686260774.git.mst@redhat.com
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=s390 olddefconfig COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang ~/bin/make.cross W=1 O=build_dir ARCH=s390 SHELL=/bin/bash drivers/block/

If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All errors (new ones prefixed by >>):

In file included from drivers/block/virtio_blk.c:10:
In file included from include/linux/virtio.h:7:
In file included from include/linux/scatterlist.h:9:
In file included from arch/s390/include/asm/io.h:75:
include/asm-generic/io.h:547:31: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]

     547 |         val = __raw_readb(PCI_IOBASE + addr);
         |                           ~~~~~~~~~~ ^
   include/asm-generic/io.h:560:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     560 |         val = __le16_to_cpu((__le16 __force)__raw_readw(PCI_IOBASE + addr));
         |                                                         ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:37:59: note: expanded from macro '__le16_to_cpu'
      37 | #define __le16_to_cpu(x) __swab16((__force __u16)(__le16)(x))
         |                                                           ^
   include/uapi/linux/swab.h:102:54: note: expanded from macro '__swab16'
     102 | #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
         |                                                      ^
   In file included from drivers/block/virtio_blk.c:10:
   In file included from include/linux/virtio.h:7:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:75:
   include/asm-generic/io.h:573:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     573 |         val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
         |                                                         ~~~~~~~~~~ ^
   include/uapi/linux/byteorder/big_endian.h:35:59: note: expanded from macro '__le32_to_cpu'
      35 | #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
         |                                                           ^
   include/uapi/linux/swab.h:115:54: note: expanded from macro '__swab32'
     115 | #define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
         |                                                      ^
   In file included from drivers/block/virtio_blk.c:10:
   In file included from include/linux/virtio.h:7:
   In file included from include/linux/scatterlist.h:9:
   In file included from arch/s390/include/asm/io.h:75:
   include/asm-generic/io.h:584:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     584 |         __raw_writeb(value, PCI_IOBASE + addr);
         |                             ~~~~~~~~~~ ^
   include/asm-generic/io.h:594:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     594 |         __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
         |                                                       ~~~~~~~~~~ ^
   include/asm-generic/io.h:604:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     604 |         __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
         |                                                       ~~~~~~~~~~ ^
   include/asm-generic/io.h:692:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     692 |         readsb(PCI_IOBASE + addr, buffer, count);
         |                ~~~~~~~~~~ ^
   include/asm-generic/io.h:700:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     700 |         readsw(PCI_IOBASE + addr, buffer, count);
         |                ~~~~~~~~~~ ^
   include/asm-generic/io.h:708:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     708 |         readsl(PCI_IOBASE + addr, buffer, count);
         |                ~~~~~~~~~~ ^
   include/asm-generic/io.h:717:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     717 |         writesb(PCI_IOBASE + addr, buffer, count);
         |                 ~~~~~~~~~~ ^
   include/asm-generic/io.h:726:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     726 |         writesw(PCI_IOBASE + addr, buffer, count);
         |                 ~~~~~~~~~~ ^
   include/asm-generic/io.h:735:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
     735 |         writesl(PCI_IOBASE + addr, buffer, count);
         |                 ~~~~~~~~~~ ^
>> drivers/block/virtio_blk.c:1283:43: error: no member named 'status' in 'struct virtblk_req'

1283 | !blk_mq_add_to_batch(req, iob, vbr->status,
| ~~~ ^
12 warnings and 1 error generated.

vim +1283 drivers/block/virtio_blk.c

1266
1267 static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
1268 {
1269 struct virtio_blk *vblk = hctx->queue->queuedata;
1270 struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx);
1271 struct virtblk_req *vbr;
1272 unsigned long flags;
1273 unsigned int len;
1274 int found = 0;
1275
1276 spin_lock_irqsave(&vq->lock, flags);
1277
1278 while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
1279 struct request *req = blk_mq_rq_from_pdu(vbr);
1280
1281 found++;
1282 if (!blk_mq_complete_request_remote(req) &&

> 1283			    !blk_mq_add_to_batch(req, iob, vbr->status,

1284 virtblk_complete_batch))
1285 virtblk_request_done(req);
1286 }
1287
1288 if (found)
1289 blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
1290
1291 spin_unlock_irqrestore(&vq->lock, flags);
1292
1293 return found;
1294 }
1295

Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
build bot
#2 lore raw
In reply to Michael S. Tsirkin
kernel test robot noticed the following build errors:

Hi Michael,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe-block/for-next]
[also build test ERROR on linus/master v6.4-rc5 next-20230608] [If your patch is applied to the wrong git tree, kindly drop us a note. And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Michael-S-Tsirkin/Revert-virtio-blk-support-completion-batching-for-the-IRQ-path/20230609-054840
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git for-next
patch link:    https://lore.kernel.org/r/9443f7273fbba6e62f89e54cbb2a70d2c93ed8e9.1686260774.git.mst%40redhat.com
patch subject: [PATCH] Revert "virtio-blk: support completion batching for the IRQ path"
config: alpha-allyesconfig (https://download.01.org/0day-ci/archive/20230609/[email protected]/config)
compiler: alpha-linux-gcc (GCC) 12.3.0

reproduce (this is a W=1 build):
mkdir -p ~/bin
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross
git remote add axboe-block https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
git fetch axboe-block for-next
git checkout axboe-block/for-next
b4 shazam https://lore.kernel.org/r/9443f7273fbba6e62f89e54cbb2a70d2c93ed8e9.1686260774.git.mst@redhat.com
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=alpha olddefconfig COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.3.0 ~/bin/make.cross W=1 O=build_dir ARCH=alpha SHELL=/bin/bash drivers/

If you fix the issue in a separate patch/commit (i.e. not just a new version of the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <[email protected]>
| Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/

All errors (new ones prefixed by >>):

drivers/block/virtio_blk.c: In function 'virtblk_poll':

>> drivers/block/virtio_blk.c:1283:55: error: 'struct virtblk_req' has no member named 'status'
    1283 |                     !blk_mq_add_to_batch(req, iob, vbr->status,
         |                                                       ^~

vim +1283 drivers/block/virtio_blk.c

1266
1267 static int virtblk_poll(struct blk_mq_hw_ctx *hctx, struct io_comp_batch *iob)
1268 {
1269 struct virtio_blk *vblk = hctx->queue->queuedata;
1270 struct virtio_blk_vq *vq = get_virtio_blk_vq(hctx);
1271 struct virtblk_req *vbr;
1272 unsigned long flags;
1273 unsigned int len;
1274 int found = 0;
1275
1276 spin_lock_irqsave(&vq->lock, flags);
1277
1278 while ((vbr = virtqueue_get_buf(vq->vq, &len)) != NULL) {
1279 struct request *req = blk_mq_rq_from_pdu(vbr);
1280
1281 found++;
1282 if (!blk_mq_complete_request_remote(req) &&

> 1283			    !blk_mq_add_to_batch(req, iob, vbr->status,

1284 virtblk_complete_batch))
1285 virtblk_request_done(req);
1286 }
1287
1288 if (found)
1289 blk_mq_start_stopped_hw_queues(vblk->disk->queue, true);
1290
1291 spin_unlock_irqrestore(&vq->lock, flags);
1292
1293 return found;
1294 }
1295

Signature · 2 lines
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki