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17 May 2024, 09:02:56 UTC
Revision 8e8320c9315c47a6a090188720ccff32a6a6ba18 authored by Jens Axboe on 20 June 2017, 23:56:13 UTC, committed by Jens Axboe on 21 June 2017, 16:17:49 UTC 
blk-mq: fix performance regression with shared tags
 
If we have shared tags enabled, then every IO completion will trigger
a full loop of every queue belonging to a tag set, and every hardware
queue for each of those queues, even if nothing needs to be done.
This causes a massive performance regression if you have a lot of
shared devices.

Instead of doing this huge full scan on every IO, add an atomic
counter to the main queue that tracks how many hardware queues have
been marked as needing a restart. With that, we can avoid looking for
restartable queues, if we don't have to.

Max reports that this restores performance. Before this patch, 4K
IOPS was limited to 22-23K IOPS. With the patch, we are running at
950-970K IOPS.

Fixes: 6d8c6c0f97ad ("blk-mq: Restart a single queue if tag sets are shared")
Reported-by: Max Gurtovoy <maxg@mellanox.com>
Tested-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Tested-by: Bart Van Assche <bart.vanassche@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 parent ec2f0fa
History
Tip revision: 8e8320c9315c47a6a090188720ccff32a6a6ba18 authored by Jens Axboe on 20 June 2017, 23:56:13 UTC
blk-mq: fix performance regression with shared tags
Tip revision: 8e8320c
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