• Jens Axboe's avatar
    blk-mq: only run the hardware queue if IO is pending · 79f720a7
    Jens Axboe authored
    Currently we are inconsistent in when we decide to run the queue. Using
    blk_mq_run_hw_queues() we check if the hctx has pending IO before
    running it, but we don't do that from the individual queue run function,
    blk_mq_run_hw_queue(). This results in a lot of extra and pointless
    queue runs, potentially, on flush requests and (much worse) on tag
    starvation situations. This is observable just looking at top output,
    with lots of kworkers active. For the !async runs, it just adds to the
    CPU overhead of blk-mq.
    
    Move the has-pending check into the run function instead of having
    callers do it.
    Reviewed-by: 's avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: 's avatarJens Axboe <axboe@kernel.dk>
    79f720a7