Hi Guys, More and more drivers want to get batching requests queued from block layer, such as mmc[1], and tcp based storage drivers[2]. Also current in-tree users have virtio-scsi, virtio-blk and nvme. For none, we already support batching dispatch. But for io scheduler, every time we just take one request from scheduler and pass the single request to blk_mq_dispatch_rq_list(). This way makes batching dispatch not possible when io scheduler is applied. One reason is that we don't want to hurt sequential IO performance, becasue IO merge chance is reduced if more requests are dequeued from scheduler queue. Tries to start the support by dequeuing more requests from scheduler if budget is enough and device isn't busy. Simple fio test over virtio-scsi shows IO can get improved by 5~10%. Patches can be found from the following tree too: https://github.com/ming1/linux/commits/v5.7-rc-blk-mq-batching-submission Patch 1 ~ 7 are improvement and cleanup, which can't applied without supporting batching dispatch. Patch 8 ~ 9 starts to support batching dispatch from scheduler. Please review and comment! [1] https://lore.kernel.org/linux-block/20200512075501.GF1531898@T590/#r [2] https://lore.kernel.org/linux-block/fe6bd8b9-6ed9-b225-f80c-314746133722@xxxxxxxxxxx/ Ming Lei (9): blk-mq: pass request queue into get/put budget callback blk-mq: pass hctx to blk_mq_dispatch_rq_list blk-mq: don't predicate last flag in blk_mq_dispatch_rq_list blk-mq: move getting driver tag and bugget into one helper blk-mq: move .queue_rq code into one helper blk-mq: move code for handling partial dispatch into one helper blk-mq: remove dead check from blk_mq_dispatch_rq_list blk-mq: pass obtained budget count to blk_mq_dispatch_rq_list blk-mq: support batching dispatch in case of io scheduler block/blk-mq-sched.c | 96 ++++++++++++++-- block/blk-mq.c | 248 +++++++++++++++++++++------------------- block/blk-mq.h | 15 +-- drivers/scsi/scsi_lib.c | 8 +- include/linux/blk-mq.h | 4 +- 5 files changed, 226 insertions(+), 145 deletions(-) Cc: Sagi Grimberg <sagi@xxxxxxxxxxx> Cc: Baolin Wang <baolin.wang7@xxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> -- 2.25.2
