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authorMike Miller <mike.miller@hp.com>2013-09-11 14:20:11 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-09-11 15:56:59 -0700
commite7b18ede4443c0207b9fd849cf604e67c6f38fc9 (patch)
treeae99ce43e9319ab14d61a68e6798f4500fb96037
parentc86db975c87976a234f13a0c2d7f931d8ede493b (diff)
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>
-rw-r--r--drivers/block/cciss.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/block/cciss.c b/drivers/block/cciss.c
index 62b6c2cc80b5..d2d95ff5353b 100644
--- a/drivers/block/cciss.c
+++ b/drivers/block/cciss.c
@@ -4258,6 +4258,13 @@ static void cciss_find_board_params(ctlr_info_t *h)
h->nr_cmds = h->max_commands - 4 - cciss_tape_cmds;
h->maxsgentries = readl(&(h->cfgtable->MaxSGElements));
/*
+ * The P600 may exhibit poor performnace under some workloads
+ * if we use the value in the configuration table. Limit this
+ * controller to MAXSGENTRIES (32) instead.
+ */
+ if (h->board_id == 0x3225103C)
+ h->maxsgentries = MAXSGENTRIES;
+ /*
* Limit in-command s/g elements to 32 save dma'able memory.
* Howvever spec says if 0, use 31
*/