From e7b18ede4443c0207b9fd849cf604e67c6f38fc9 Mon Sep 17 00:00:00 2001 From: Mike Miller Date: Wed, 11 Sep 2013 14:20:11 -0700 Subject: [PATCH] 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 Signed-off-by: Dwight (Bud) Brown Signed-off-by: Tomas Henzl Acked-by: Stephen M. Cameron Cc: Jens Axboe Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/cciss.c | 7 +++++++ 1 file changed, 7 insertions(+) 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 @@ -4257,6 +4257,13 @@ static void cciss_find_board_params(ctlr_info_t *h) cciss_get_max_perf_mode_cmds(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 -- 2.20.1