Hi Jens, 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%. Baolin has tested previous versions and found performance on MMC can be improved. Patch 1 ~ 4 are improvement and cleanup, which can't applied without supporting batching dispatch. Patch 5 ~ 6 starts to support batching dispatch from scheduler. [1] https://lore.kernel.org/linux-block/20200512075501.GF1531898@T590/#r [2] https://lore.kernel.org/linux-block/fe6bd8b9-6ed9-b225-f80c-314746133722@xxxxxxxxxxx/ V5: - code style changes suggested by Damien V4: - fix releasing budgets and avoids IO hang(5/6) - dispatch more batches if the device can accept more(6/6) - verified by running more tests V3: - add reviewed-by tag - fix one typo - fix one budget leak issue in case that .queue_rq returned *_RESOURCE in 5/6 V2: - remove 'got_budget' from blk_mq_dispatch_rq_list - drop patch for getting driver tag & handling partial dispatch Ming Lei (6): blk-mq: pass request queue into get/put budget callback blk-mq: pass hctx to blk_mq_dispatch_rq_list blk-mq: move getting driver tag and budget 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 | 116 +++++++++++++++++++++++++++++++++++----- block/blk-mq.c | 110 +++++++++++++++++++++++-------------- block/blk-mq.h | 15 +++--- drivers/scsi/scsi_lib.c | 8 ++- include/linux/blk-mq.h | 4 +- 5 files changed, 182 insertions(+), 71 deletions(-) Cc: Sagi Grimberg <sagi@xxxxxxxxxxx> Cc: Baolin Wang <baolin.wang7@xxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> -- 2.25.2
