On 06/04/2021 04:19, Ming Lei wrote: Hi Ming,
Yanhui found that write performance is degraded a lot after applying hctx shared tagset on one test machine with megaraid_sas. And turns out it is caused by none scheduler which becomes default elevator caused by hctx shared tagset patchset. Given more scsi HBAs will apply hctx shared tagset, and the similar performance exists for them too. So keep previous behavior by still using default mq-deadline for queues which apply hctx shared tagset, just like before.
I think that there a some SCSI HBAs which have nr_hw_queues > 1 and don't use shared sbitmap - do you think that they want want this as well (without knowing it)?
IIRC, the upcoming broadcom SCSI HBA driver does this. Thanks, John
Fixes: 32bc15afed04 ("blk-mq: Facilitate a shared sbitmap per tagset") Reported-by: Yanhui Ma <yama@xxxxxxxxxx> Cc: John Garry <john.garry@xxxxxxxxxx> Cc: Hannes Reinecke <hare@xxxxxxx> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> --- block/elevator.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/block/elevator.c b/block/elevator.c index 293c5c81397a..440699c28119 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -621,7 +621,8 @@ static inline bool elv_support_iosched(struct request_queue *q) */ static struct elevator_type *elevator_get_default(struct request_queue *q) { - if (q->nr_hw_queues != 1) + if (q->nr_hw_queues != 1 && + !blk_mq_is_sbitmap_shared(q->tag_set->flags)) return NULL;return elevator_get(q, "mq-deadline", false);
