diff options
Diffstat (limited to 'blk-loop-avoid-too-many-pending-work-IO.patch')
| -rw-r--r-- | blk-loop-avoid-too-many-pending-work-IO.patch | 106 |
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; + }; + |