Messages in this thread | | | Date | Mon, 18 Dec 2017 12:34:26 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] Pass the task_struct explicitly to delayacct_blkio_end |
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On Fri, Dec 15, 2017 at 06:11:43PM +0000, Josh Snyder wrote:
> Subject: [PATCH] Pass the task_struct explicitly to delayacct_blkio_end
That subject is crap; it needs a subsystem prefix and it needs to describe what is done, not how its done.
Something like:
delayacct: Fix double accounting for blk-io
> Before e33a9bba85a8, 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.
The correct way to quote a commit is like:
e33a9bba85a8 ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler")
> 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_struct.
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