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SubjectRe: Added in stricter no merge semantics for block I/O
On Tue, Jan 26 2010, Alan D. Brunelle wrote:
> 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>
> Cc: jens.axboe@oracle.com
> ---
> Documentation/ABI/testing/sysfs-block | 14 ++++++++++++++
> Documentation/block/queue-sysfs.txt | 10 +++++-----
> block/blk-sysfs.c | 11 +++++++----
> block/elevator.c | 11 ++++++++++-
> include/linux/blkdev.h | 3 +++
> 5 files changed, 39 insertions(+), 10 deletions(-)

Thanks Alan, I think this is a good addition, I have often before hacked
up the "no merges at all" logic for testing purposes as well. I have
queued it up for 2.6.34.

--
Jens Axboe



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