mtip32xx: avoid to read HOST_CAP from HW in .queue_rq()
commit8a05aa4ce3bf767b7bd72851da89c23d084d1ecb
authorMing Lei <ming.lei@redhat.com>
Wed, 5 Jul 2017 04:14:27 +0000 (5 12:14 +0800)
committerJens Axboe <axboe@kernel.dk>
Wed, 5 Jul 2017 18:11:26 +0000 (5 12:11 -0600)
tree2ad465f735488c668d1193d02c066ba3f3b00863
parentea4d12dabf872b496218cdc8e7874feef8676cdd
mtip32xx: avoid to read HOST_CAP from HW in .queue_rq()

It is observed reading the register from HW takes a bit long,
for example in my box, the following difference of 'perf report
--no-children fio ...' can be seen when running I/O:

1) V4.12 without patch
+    9.28%       fio  [mtip32xx]           [k] mtip_irq_handler
+    8.48%       fio  [mtip32xx]           [k] mtip_init_cmd_header

2) V4.12 with the following patch
+    9.14%       fio  [mtip32xx]           [k] mtip_irq_handler
......
+    1.14%       fio  [mtip32xx]           [k] mtip_init_cmd_header

IOPS can be increased by ~5% with this patch too.

Fixes: a4e84aae8139(mtip32xx: use runtime tag to initialize command header)
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
drivers/block/mtip32xx/mtip32xx.c
drivers/block/mtip32xx/mtip32xx.h