Hello, On Mon, Dec 18, 2017 at 04:15:10PM +0000, Josh Snyder wrote: > Before commit e33a9bba85a8 ("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 e33a9bba85a8, 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 upon `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. > > Fixes: e33a9bba85a8 ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler") > Signed-off-by: Josh Snyder <joshs@xxxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks. -- tejun