linux-kernel - Re: [RFC PATCH v2] sched/deadline: Add more reschedule cases to prio_changed

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Date:   Thu, 9 Feb 2023 14:07:19 +0100
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Juri Lelli <juri.lelli@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Eder Zulian <ezulian@...hat.com>
Subject: Re: [RFC PATCH v2] sched/deadline: Add more reschedule cases to
 prio_changed_dl()

On 2/7/23 12:58, Juri Lelli wrote:
> Hi,
> 
> On 06/02/23 14:06, Valentin Schneider wrote:
>> I've been tracking down an issue on a ~5.17ish kernel where:
>>
>>   CPUx                           CPUy
>>
>>   <DL task p0 owns an rtmutex M>
>>   <p0 depletes its runtime, gets throttled>
>>   <rq switches to the idle task>
>> 				 <DL task p1 blocks on M, boost/replenish p0>
>> 				 <No call to resched_curr() happens here>
>>
>>   [idle task keeps running here until *something*
>>    accidentally sets TIF_NEED_RESCHED]
>>
>> On that kernel, it is quite easy to trigger using rt-tests's deadline_test
>> [1] with the test running on isolated CPUs (this reduces the chance of
>> something unrelated setting TIF_NEED_RESCHED on the idle tasks, making the
>> issue even more obvious as the hung task detector chimes in).
>>
>> I haven't been able to reproduce this using a mainline kernel, even if I
>> revert
>>
>>   2972e3050e35 ("tracing: Make trace_marker{,_raw} stream-like")
>>
>> which gets rid of the lock involved in the above test, *but* I cannot
>> convince myself the issue isn't there from looking at the code.
>>
>> Make prio_changed_dl() issue a reschedule if the current task isn't a
>> deadline one. While at it, ensure a reschedule is emitted when a
>> queued-but-not-current task gets boosted with an earlier deadline that
>> current's.
>>
>> [1]: https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git
>> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
>> ---
> This looks now good to me, thanks!
> 
> Acked-by: Juri Lelli <juri.lelli@...hat.com>

Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>

-- Daniel