From d97e594c51660bea510a387731637b894651e4b5 Mon Sep 17 00:00:00 2001 From: John Garry Date: Thu, 13 May 2021 20:00:58 +0800 Subject: blk-mq: Use request queue-wide tags for tagset-wide sbitmap The tags used for an IO scheduler are currently per hctx. As such, when q->nr_hw_queues grows, so does the request queue total IO scheduler tag depth. This may cause problems for SCSI MQ HBAs whose total driver depth is fixed. Ming and Yanhui report higher CPU usage and lower throughput in scenarios where the fixed total driver tag depth is appreciably lower than the total scheduler tag depth: https://lore.kernel.org/linux-block/440dfcfc-1a2c-bd98-1161-cec4d78c6dfc@huawei.com/T/#mc0d6d4f95275a2743d1c8c3e4dc9ff6c9aa3a76b In that scenario, since the scheduler tag is got first, much contention is introduced since a driver tag may not be available after we have got the sched tag. Improve this scenario by introducing request queue-wide tags for when a tagset-wide sbitmap is used. The static sched requests are still allocated per hctx, as requests are initialised per hctx, as in blk_mq_init_request(..., hctx_idx, ...) -> set->ops->init_request(.., hctx_idx, ...). For simplicity of resizing the request queue sbitmap when updating the request queue depth, just init at the max possible size, so we don't need to deal with the possibly with swapping out a new sbitmap for old if we need to grow. Signed-off-by: John Garry Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/1620907258-30910-3-git-send-email-john.garry@huawei.com Signed-off-by: Jens Axboe --- include/linux/blkdev.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'include/linux/blkdev.h') diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index f69c75bd6d27..2c28577b50f4 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -25,6 +25,7 @@ #include #include #include +#include struct module; struct scsi_ioctl_command; @@ -493,6 +494,9 @@ struct request_queue { atomic_t nr_active_requests_shared_sbitmap; + struct sbitmap_queue sched_bitmap_tags; + struct sbitmap_queue sched_breserved_tags; + struct list_head icq_list; #ifdef CONFIG_BLK_CGROUP DECLARE_BITMAP (blkcg_pols, BLKCG_MAX_POLS); -- cgit v1.2.3