• Josh Snyder's avatar
    delayacct: Account blkio completion on the correct task · c96f5471
    Josh Snyder authored
    Before commit:
    
      e33a9bba ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler")
    
    delayacct_blkio_end() was called after context-switching into the task which
    completed I/O.
    
    This resulted in double counting: the task would account a delay both waiting
    for I/O and for time spent in the runqueue.
    
    With e33a9bba
    
    , delayacct_blkio_end() is called by try_to_wake_up().
    In ttwu, we have not yet context-switched. This is more correct, in that
    the delay accounting ends when the I/O is complete.
    
    But delayacct_blkio_end() relies on 'get_current()', and we have not yet
    context-switched into the task whose I/O completed. This results in the
    wrong task having its delay accounting statistics updated.
    
    Instead of doing that, pass the task_struct being woken to delayacct_blkio_end(),
    so that it can update the statistics of the correct task.
    Signed-off-by: default avatarJosh Snyder <joshs@netflix.com>
    Acked-by: default avatarTejun Heo <tj@kernel.org>
    Acked-by: default avatarBalbir Singh <bsingharora@gmail.com>
    Cc: <stable@vger.kernel.org>
    Cc: Brendan Gregg <bgregg@netflix.com>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: linux-block@vger.kernel.org
    Fixes: e33a9bba ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler")
    Link: http://lkml.kernel.org/r/1513613712-571-1-git-send-email-joshs@netflix.com
    
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    c96f5471
core.c 171 KB