From: Jens Axboe <axboe@fb.com>
Date: Mon, 19 May 2014 15:23:55 +0000 (-0600)
Subject: blk-mq: switch ctx pending map to the sparser blk_align_bitmap
X-Git-Tag: omap-for-v3.16/fixes-against-rc1~39^2~49^2~37
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1429d7c9467e1e3de0b0ff91d7e4d67c1a92f8a3;p=pandora-kernel.git

blk-mq: switch ctx pending map to the sparser blk_align_bitmap

Each hardware queue has a bitmap of software queues with pending
requests. When new IO is queued on a software queue, the bit is
set, and when IO is pruned on a hardware queue run, the bit is
cleared. This causes a lot of traffic. Switch this from the regular
BITS_PER_LONG bitmap to a sparser layout, similarly to what was
done for blk-mq tagging.

20% performance increase was observed for single threaded IO, and
about 15% performanc increase on multiple threads driving the
same device.

Signed-off-by: Jens Axboe <axboe@fb.com>
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