block: strict_rq affinity

Some systems benefit from completions always being steered to the strict
requester cpu rather than the looser "per-socket" steering that
blk_cpu_to_group() attempts by default. This is because the first
CPU in the group mask ends up being completely overloaded with work,
while the others (including the original submitter) has power left
to spare.

Allow the strict mode to be set by writing '2' to the sysfs control
file. This is identical to the scheme used for the nomerges file,
where '2' is a more aggressive setting than just being turned on.

echo 2 > /sys/block/<bdev>/queue/rq_affinity

Change-Id: Iafa796c31d0c4bafb4a74f9c0efa02ab591b6abd
Signed-off-by: zwliew <zhaoweiliew@gmail.com>
defconfig: enabled RCU Boost and THUMBEE

Change-Id: I2a6e038cd65a3cd11c6abce6e7ac5dcc8537d6a6
Signed-off-by: zwliew <zhaoweiliew@gmail.com>