tree 51a4858ffc7562126e4d26b32586739e1ff67766
parent 650cdb50b04ffbeb43490e6c0d8b164e37159e02
author Shaohua Li <shli@kernel.org> 1381799104 +0800
committer Jens Axboe <axboe@kernel.dk> 1381850110 -0600

blk-mq: switch to percpu-ida for tag management

Using percpu-ida to manage blk-mq tags. the percpu-ida has similar algorithm
like the blk-mq-tag. The difference is when a cpu can't allocate tags
blk-mq-tag uses ipi to purge remote cpu cache and percpu-ida directly purges
remote cpu cache. In practice (testing null_blk), the percpu-ida approach is
much faster when total tags aren't enough.

My test is done in a 2 sockets machine, 12 process cross the 2 sockets. So if
there is lock contention or ipi, should be stressed heavily. Testing is done
for null-blk.

hw_queue_depth	nopatch iops	patch iops
64		~800k/s		~1470k/s
2048		~4470k/s	~4340k/s

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