tree ad0340b201405fb19eaa7c8e6af0ac395e3dc8bd
parent 407ac95e2271a310016ced97f407676e79c53c06
author Shaohua Li <shli@fusionio.com> 1333733867 -0600
committer Jens Axboe <axboe@kernel.dk> 1333733867 -0600

block: make auto block plug flush threshold per-disk based

We do auto block plug flush to reduce latency, the threshold is 16
requests. This works well if the task is accessing one or two drives.
The problem is if the task is accessing a raid 0 device and the raid
disk number is big, say 8 or 16, 16/8 = 2 or 16/16=1, we will have
heavy lock contention.

This patch makes the threshold per-disk based. The latency should be
still ok accessing one or two drives. The setup with application
accessing a lot of drives in the meantime uaually is big machine,
avoiding lock contention is more important, because any contention
will actually increase latency.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>