Ming Lei 8a05aa4ce3 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>
2017-07-05 12:11:26 -06:00
2017-07-02 16:07:02 -07:00

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