On Tue, Feb 08, 2022 at 10:36:55AM -0500, Emanuele Giuseppe Esposito wrote:
> If a drain happens while a job is sleeping, the timeout
> gets cancelled and the job continues once the drain ends.
> This is especially bad for the sleep performed in commit and stream
> jobs, since that is dictated by ratelimit to maintain a certain speed.
>
> Basically the execution path is the following:
> 1. job calls job_sleep_ns, and yield with a timer in @ns ns.
> 2. meanwhile, a drain is executed, and
> child_job_drained_{begin/end} could be executed as ->drained_begin()
> and ->drained_end() callbacks.
> Therefore child_job_drained_begin() enters the job, that continues
> execution in job_sleep_ns() and calls job_pause_point_locked().
> 3. job_pause_point_locked() detects that we are in the middle of a
> drain, and firstly deletes any existing timer and then yields again,
> waiting for ->drained_end().
> 4. Once draining is finished, child_job_drained_end() runs and resumes
> the job. At this point, the timer has been lost and we just resume
> without checking if enough time has passed.
>
> This fix implies that from now onwards, job_sleep_ns will force the job
> to sleep @ns, even if it is wake up (purposefully or not) in the middle
> of the sleep. Therefore qemu-iotests test might run a little bit slower,
> depending on the speed of the job. Setting a job speed to values like "1"
> is not allowed anymore (unless you want to wait forever).
>
> Because of this fix, test_stream_parallel() in tests/qemu-iotests/030
> takes too long, since speed of stream job is just 1024 and before
> it was skipping all the wait thanks to the drains. Increase the
> speed to 256 * 1024. Exactly the same happens for test 151.
>
> Instead we need to sleep less in test_cancel_ready() test-blockjob.c,
> so that the job will be able to exit the sleep and transition to ready
> before the main loop asserts.
>
> Signed-off-by: Emanuele Giuseppe Esposito <eespo...@redhat.com>
> ---
> job.c | 19 +++++++++++--------
> tests/qemu-iotests/030 | 2 +-
> tests/qemu-iotests/151 | 4 ++--
> tests/unit/test-blockjob.c | 2 +-
> 4 files changed, 15 insertions(+), 12 deletions(-)Acked-by: Stefan Hajnoczi <stefa...@redhat.com>
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