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Date:   Mon, 23 Mar 2020 10:27:54 +0100
From:   Juri Lelli <juri.lelli@redhat.com>
To:     Lucas Stach <l.stach@pengutronix.de>
Cc:     Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>
Subject: Re: help needed in debugging missed wakeup(?)
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Hi,

On 20/03/20 20:04, Lucas Stach wrote:

[...]

> My hope was that someone would could guide me a little with an educated
> guess, to make those trace_printks more helpful. The lockup is hard to
> trigger and there's other unrelated system activity going on, even when
> the relevant user task is stuck, so randomly sprinkling debug
> statements will generate lots of output to filter down.

I'd start by enabling sched:sched_pi_setprio (or adding trace_printks
around there to confirm your suspicion). Once that is confirmed, I'd try
to look at update_curr_dl::throttle and verify if the misbehaving task
was indeed throttled at some point; it shouldn't be, because dl_boosted
flag should be set for it at this point (maybe check this condition as
well).

Best,

Juri