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| author | Alan D. Brunelle <Alan.Brunelle@hp.com> | 2010-01-29 09:04:08 +0100 |
|---|---|---|
| committer | Jens Axboe <jens.axboe@oracle.com> | 2010-01-29 09:04:08 +0100 |
| commit | 488991e28e55b4fbca8067edf0259f69d1a6f92c (patch) | |
| tree | fea5e0aca42e338137cc050e66aaeb5f539e3d21 /Documentation/block | |
| parent | 47483e25205f1f8d79784f0f7c733941bc080ec0 (diff) | |
| download | lwn-488991e28e55b4fbca8067edf0259f69d1a6f92c.tar.gz lwn-488991e28e55b4fbca8067edf0259f69d1a6f92c.zip | |
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>
Diffstat (limited to 'Documentation/block')
| -rw-r--r-- | Documentation/block/queue-sysfs.txt | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt index e164403f60e1..f65274081c8d 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) ---------------- |