On 07/04/2017 10:14 PM, Ming Lei wrote:

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.

Thanks, this is definitely problematic since we don't just do it
at init time anymore. Applied for 4.13.

-- 
Jens Axboe