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authorAlan D. Brunelle <Alan.Brunelle@hp.com>2010-01-29 09:04:08 +0100
committerJens Axboe <jens.axboe@oracle.com>2010-01-29 09:04:08 +0100
commit488991e28e55b4fbca8067edf0259f69d1a6f92c (patch)
treefea5e0aca42e338137cc050e66aaeb5f539e3d21
parent47483e25205f1f8d79784f0f7c733941bc080ec0 (diff)
block: Added in stricter no merge semantics for block I/O
Updated 'nomerges' tunable to accept a value of '2' - indicating that _no_ merges at all are to be attempted (not even the simple one-hit cache). The following table illustrates the additional benefit - 5 minute runs of a random I/O load were applied to a dozen devices on a 16-way x86_64 system. nomerges Throughput %System Improvement (tput / %sys) -------- ------------ ----------- ------------------------- 0 12.45 MB/sec 0.669365609 1 12.50 MB/sec 0.641519199 0.40% / 2.71% 2 12.52 MB/sec 0.639849750 0.56% / 2.96% Signed-off-by: Alan D. Brunelle <alan.brunelle@hp.com> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
-rw-r--r--Documentation/ABI/testing/sysfs-block14
-rw-r--r--Documentation/block/queue-sysfs.txt10
-rw-r--r--block/blk-sysfs.c11
-rw-r--r--block/elevator.c11
-rw-r--r--include/linux/blkdev.h3
5 files changed, 39 insertions, 10 deletions
diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index d2f90334bb9..4873c759d53 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -128,3 +128,17 @@ Description:
preferred request size for workloads where sustained
throughput is desired. If no optimal I/O size is
reported this file contains 0.
+
+What: /sys/block/<disk>/queue/nomerges
+Date: January 2010
+Contact:
+Description:
+ Standard I/O elevator operations include attempts to
+ merge contiguous I/Os. For known random I/O loads these
+ attempts will always fail and result in extra cycles
+ being spent in the kernel. This allows one to turn off
+ this behavior on one of two ways: When set to 1, complex
+ merge checks are disabled, but the simple one-shot merges
+ with the previous I/O request are enabled. When set to 2,
+ all merge tries are disabled. The default value is 0 -
+ which enables all types of merge tries.
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index e164403f60e..f65274081c8 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -25,11 +25,11 @@ size allowed by the hardware.
nomerges (RW)
-------------
-This enables the user to disable the lookup logic involved with IO merging
-requests in the block layer. Merging may still occur through a direct
-1-hit cache, since that comes for (almost) free. The IO scheduler will not
-waste cycles doing tree/hash lookups for merges if nomerges is 1. Defaults
-to 0, enabling all merges.
+This enables the user to disable the lookup logic involved with IO
+merging requests in the block layer. By default (0) all merges are
+enabled. When set to 1 only simple one-hit merges will be tried. When
+set to 2 no merge algorithms will be tried (including one-hit or more
+complex tree/hash lookups).
nr_requests (RW)
----------------
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 8606c9543fd..e85442415db 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -189,7 +189,8 @@ static ssize_t queue_nonrot_store(struct request_queue *q, const char *page,
static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
{
- return queue_var_show(blk_queue_nomerges(q), page);
+ return queue_var_show((blk_queue_nomerges(q) << 1) |
+ blk_queue_noxmerges(q), page);
}
static ssize_t queue_nomerges_store(struct request_queue *q, const char *page,
@@ -199,10 +200,12 @@ static ssize_t queue_nomerges_store(struct request_queue *q, const char *page,
ssize_t ret = queue_var_store(&nm, page, count);
spin_lock_irq(q->queue_lock);
- if (nm)
+ queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
+ queue_flag_clear(QUEUE_FLAG_NOXMERGES, q);
+ if (nm == 2)
queue_flag_set(QUEUE_FLAG_NOMERGES, q);
- else
- queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
+ else if (nm)
+ queue_flag_set(QUEUE_FLAG_NOXMERGES, q);
spin_unlock_irq(q->queue_lock);
return ret;
diff --git a/block/elevator.c b/block/elevator.c
index 9ad5ccc4c5e..ee3a883840f 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -474,6 +474,15 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
int ret;
/*
+ * Levels of merges:
+ * nomerges: No merges at all attempted
+ * noxmerges: Only simple one-hit cache try
+ * merges: All merge tries attempted
+ */
+ if (blk_queue_nomerges(q))
+ return ELEVATOR_NO_MERGE;
+
+ /*
* First try one-hit cache.
*/
if (q->last_merge) {
@@ -484,7 +493,7 @@ int elv_merge(struct request_queue *q, struct request **req, struct bio *bio)
}
}
- if (blk_queue_nomerges(q))
+ if (blk_queue_noxmerges(q))
return ELEVATOR_NO_MERGE;
/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ffb13ad3571..f71f5c58620 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -463,6 +463,7 @@ struct request_queue
#define QUEUE_FLAG_IO_STAT 15 /* do IO stats */
#define QUEUE_FLAG_CQ 16 /* hardware does queuing */
#define QUEUE_FLAG_DISCARD 17 /* supports DISCARD */
+#define QUEUE_FLAG_NOXMERGES 18 /* No extended merges */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_CLUSTER) | \
@@ -589,6 +590,8 @@ enum {
#define blk_queue_queuing(q) test_bit(QUEUE_FLAG_CQ, &(q)->queue_flags)
#define blk_queue_stopped(q) test_bit(QUEUE_FLAG_STOPPED, &(q)->queue_flags)
#define blk_queue_nomerges(q) test_bit(QUEUE_FLAG_NOMERGES, &(q)->queue_flags)
+#define blk_queue_noxmerges(q) \
+ test_bit(QUEUE_FLAG_NOXMERGES, &(q)->queue_flags)
#define blk_queue_nonrot(q) test_bit(QUEUE_FLAG_NONROT, &(q)->queue_flags)
#define blk_queue_io_stat(q) test_bit(QUEUE_FLAG_IO_STAT, &(q)->queue_flags)
#define blk_queue_flushing(q) ((q)->ordseq)