Re: Added in stricter no merge semantics for block I/O

[Jens Axboe <jens.axboe@oracle.com>]

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