• Tejun Heo's avatar
    blk-mq: add optional request->alloc_time_ns · 6f816b4b
    Tejun Heo authored
    
    
    There are currently two start time timestamps - start_time_ns and
    io_start_time_ns.  The former marks the request allocation and and the
    second issue-to-device time.  The planned io.weight controller needs
    to measure the total time bios take to execute after it leaves rq_qos
    including the time spent waiting for request to become available,
    which can easily dominate on saturated devices.
    
    This patch adds request->alloc_time_ns which records when the request
    allocation attempt started.  As it isn't used for the usual stats,
    make it optional behind CONFIG_BLK_RQ_ALLOC_TIME and
    QUEUE_FLAG_RQ_ALLOC_TIME so that it can be compiled out when there are
    no users and it's active only on queues which need it even when
    compiled in.
    
    v2: s/pre_start_time/alloc_time/ and add CONFIG_BLK_RQ_ALLOC_TIME
        gating as suggested by Jens.
    
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    6f816b4b