• Mikulas Patocka's avatar
    block: delete part_round_stats and switch to less precise counting · 5b18b5a7
    Mikulas Patocka authored
    We want to convert to per-cpu in_flight counters.
    
    The function part_round_stats needs the in_flight counter every jiffy, it
    would be too costly to sum all the percpu variables every jiffy, so it
    must be deleted. part_round_stats is used to calculate two counters -
    time_in_queue and io_ticks.
    
    time_in_queue can be calculated without part_round_stats, by adding the
    duration of the I/O when the I/O ends (the value is almost as exact as the
    previously calculated value, except that time for in-progress I/Os is not
    counted).
    
    io_ticks can be approximated by increasing the value when I/O is started
    or ended and the jiffies value has changed. If the I/Os take less than a
    jiffy, the value is as exact as the previously calculated value. If the
    I/Os take more than a jiffy, io_ticks can drift behind the previously
    calculated value.
    Signed-off-by: default avatarMikulas Patocka <[email protected]>
    Signed-off-by: default avatarMike Snitzer <[email protected]>
    Signed-off-by: default avatarJens Axboe <[email protected]>
    5b18b5a7
blk-core.c 47.5 KB