cciss: set max scatter gather entries to 32 on P600
authorMike Miller <mike.miller@hp.com>
Wed, 11 Sep 2013 21:20:11 +0000 (14:20 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 11 Sep 2013 22:56:59 +0000 (15:56 -0700)
commite7b18ede4443c0207b9fd849cf604e67c6f38fc9
treeae99ce43e9319ab14d61a68e6798f4500fb96037
parentc86db975c87976a234f13a0c2d7f931d8ede493b
cciss: set max scatter gather entries to 32 on P600

At one time we used to set the maximum number of scatter gather elements
on all Smart Array controllers to 32.  At some point in time the
firmware began to write the "appropriate" value for each controller into
the config table.  The cciss driver would then read that and set
h->maxsgentries.

        h->maxsgentries = readl(&(h->cfgtable->MaxSGElements);

On the P600 that value is 544.  Under some workloads a significant
performance reduction may result.  This patch forces the P600 to use
only 32 scatter gather elements.  Other controllers are not affected.

Signed-off-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: Dwight (Bud) Brown <bubrown@redhat.com>
Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Stephen M. Cameron <steve.cameron@hp.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/block/cciss.c