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authorJosh Boyer <jwboyer@fedoraproject.org>2015-06-26 09:33:38 -0400
committerJosh Boyer <jwboyer@fedoraproject.org>2015-06-26 09:33:38 -0400
commit35eff41288ccf2a1ddd555db0b0e51906af970a0 (patch)
tree761d7f671ba27b4a314aa72a864f9a3a56dc7d5b /blk-loop-avoid-too-many-pending-work-IO.patch
parent21694f1b769f352163ed762b519cc7155dd1c97d (diff)
downloadkernel-35eff41288ccf2a1ddd555db0b0e51906af970a0.tar.gz
kernel-35eff41288ccf2a1ddd555db0b0e51906af970a0.tar.xz
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Linux v4.1-5596-gaefbef10e3ae
Diffstat (limited to 'blk-loop-avoid-too-many-pending-work-IO.patch')
-rw-r--r--blk-loop-avoid-too-many-pending-work-IO.patch106
1 files changed, 106 insertions, 0 deletions
diff --git a/blk-loop-avoid-too-many-pending-work-IO.patch b/blk-loop-avoid-too-many-pending-work-IO.patch
new file mode 100644
index 000000000..568fc6b9c
--- /dev/null
+++ b/blk-loop-avoid-too-many-pending-work-IO.patch
@@ -0,0 +1,106 @@
+From: Ming Lei <ming.lei@canonical.com>
+Date: Tue, 28 Apr 2015 14:40:49 -0400
+Subject: [PATCH] blk: loop: avoid too many pending work IO
+
+If there are too many pending per work I/O, too many
+high priority work thread can be generated so that
+system performance can be effected.
+
+This patch limits the max pending per work I/O as 16,
+and will fackback to single queue mode when the max
+number is reached.
+
+This patch fixes Fedora 22 live booting performance
+regression when it is booted from squashfs over dm
+based on loop, and looks the following reasons are
+related with the problem:
+
+- not like other filesyststems(such as ext4), squashfs
+is a bit special, and I observed that increasing I/O jobs
+to access file in squashfs only improve I/O performance a
+little, but it can make big difference for ext4
+
+- nested loop: both squashfs.img and ext3fs.img are mounted
+as loop block, and ext3fs.img is inside the squashfs
+
+- during booting, lots of tasks may run concurrently
+
+Fixes: b5dd2f6047ca108001328aac0e8588edd15f1778
+Cc: stable@vger.kernel.org (v4.0)
+Reported-by: Justin M. Forbes <jforbes@fedoraproject.org>
+Tested-by: Justin M. Forbes <jforbes@fedoraproject.org>
+Signed-off-by: Ming Lei <ming.lei@canonical.com>
+---
+ drivers/block/loop.c | 19 +++++++++++++++++--
+ drivers/block/loop.h | 2 ++
+ 2 files changed, 19 insertions(+), 2 deletions(-)
+
+diff --git a/drivers/block/loop.c b/drivers/block/loop.c
+index d7173cb1ea76..4db0301420b0 100644
+--- a/drivers/block/loop.c
++++ b/drivers/block/loop.c
+@@ -1425,13 +1425,24 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
+ const struct blk_mq_queue_data *bd)
+ {
+ struct loop_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
++ struct loop_device *lo = cmd->rq->q->queuedata;
++ bool single_queue = !!(cmd->rq->cmd_flags & REQ_WRITE);
++
++ /*
++ * Fallback to single queue mode if the pending per work
++ * I/O number reaches 32, otherwise too many high priority
++ * worker thread may effect system performance as reported
++ * in fedora live booting from squashfs over loop.
++ */
++ if (atomic_read(&lo->pending_per_work_io) >= 32)
++ single_queue = true;
+
+ blk_mq_start_request(bd->rq);
+
+- if (cmd->rq->cmd_flags & REQ_WRITE) {
+- struct loop_device *lo = cmd->rq->q->queuedata;
++ if (single_queue) {
+ bool need_sched = true;
+
++ cmd->per_work_io = false;
+ spin_lock_irq(&lo->lo_lock);
+ if (lo->write_started)
+ need_sched = false;
+@@ -1443,6 +1454,8 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
+ if (need_sched)
+ queue_work(loop_wq, &lo->write_work);
+ } else {
++ cmd->per_work_io = true;
++ atomic_inc(&lo->pending_per_work_io);
+ queue_work(loop_wq, &cmd->read_work);
+ }
+
+@@ -1467,6 +1480,8 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
+ if (ret)
+ cmd->rq->errors = -EIO;
+ blk_mq_complete_request(cmd->rq);
++ if (cmd->per_work_io)
++ atomic_dec(&lo->pending_per_work_io);
+ }
+
+ static void loop_queue_write_work(struct work_struct *work)
+diff --git a/drivers/block/loop.h b/drivers/block/loop.h
+index 301c27f8323f..eb855f57a62d 100644
+--- a/drivers/block/loop.h
++++ b/drivers/block/loop.h
+@@ -57,6 +57,7 @@ struct loop_device {
+ struct list_head write_cmd_head;
+ struct work_struct write_work;
+ bool write_started;
++ atomic_t pending_per_work_io;
+ int lo_state;
+ struct mutex lo_ctl_mutex;
+
+@@ -68,6 +69,7 @@ struct loop_device {
+ struct loop_cmd {
+ struct work_struct read_work;
+ struct request *rq;
++ bool per_work_io;
+ struct list_head list;
+ };
+