• Ming Lei's avatar
    blk-mq: insert request not through ->queue_rq into sw/scheduler queue · db03f88f
    Ming Lei authored
    c616cbee ("blk-mq: punt failed direct issue to dispatch list") supposed
    to add request which has been through ->queue_rq() to the hw queue dispatch
    list, however it adds request running out of budget or driver tag to hw queue
    too. This way basically bypasses request merge, and causes too many request
    dispatched to LLD, and system% is unnecessary increased.
    
    Fixes this issue by adding request not through ->queue_rq into sw/scheduler
    queue, and this way is safe because no ->queue_rq is called on this request
    yet.
    
    High %system can be observed on Azure storvsc device, and even soft lock
    is observed. This patch reduces %system during heavy sequential IO,
    meantime decreases soft lockup risk.
    
    Fixes: c616cbee ("blk-mq: punt failed direct issue to dispatch list")
    Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
    Cc: Christoph Hellwig <hch@lst.de>
    Cc: Bart Van Assche <bvanassche@acm.org>
    Cc: Mike Snitzer <snitzer@redhat.com>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    db03f88f
blk-mq.c 96.5 KB