In [0], Kashyap reports high CPU usage for blk_mq_queue_tag_busy_iter() and callees for shared tags. Indeed blk_mq_queue_tag_busy_iter() would be less optimum for moving to shared tags, but it was not optimum previously. So I would like this series tested, and also to know what is triggering blk_mq_queue_tag_busy_iter() from userspace to cause such high CPU loading. As suggested by Ming, reading /proc/diskstats in a while true loop can trigger blk_mq_queue_tag_busy_iter(); I do so in a test with 2x separate consoles, and here are the results: v5.15 blk_mq_queue_tag_busy_iter() 6.2% part_stat_read_all() 6.7 pre-v5.16 (Linus' master branch @ commit bfc484fe6abb) blk_mq_queue_tag_busy_iter() 4.5% part_stat_read_all() 6.2 pre-v5.16+this series blk_mq_queue_tag_busy_iter() not shown in top users part_stat_read_all() 7.5% These results are from perf top, on a system with 7x disks, with hisi_sas which has 16x HW queues. [0] https://lore.kernel.org/linux-block/e4e92abbe9d52bcba6b8cc6c91c442cc@xxxxxxxxxxxxxx/ John Garry (3): blk-mq: Drop busy_iter_fn blk_mq_hw_ctx argument blk-mq: Delete busy_iter_fn blk-mq: Optimise blk_mq_queue_tag_busy_iter() for shared tags block/blk-mq-tag.c | 58 +++++++++++++++++++++++++++--------------- block/blk-mq-tag.h | 2 +- block/blk-mq.c | 17 ++++++------- include/linux/blk-mq.h | 2 -- 4 files changed, 47 insertions(+), 32 deletions(-) -- 2.17.1
