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Date: Wed, 29 May 2024 12:55:28 +0200
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	linux-mm@kvack.org, Phil Auld <pauld@redhat.com>
Subject: Re: [PATCH v2] sched/rt: Clean up usage of rt_task()
Message-ID: <20240529105528.9QBTCqCr@linutronix.de>
References: <20240515220536.823145-1-qyousef@layalina.io>
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 <20240527172650.kieptfl3zhyljkzx@airbuntu>
 <20240529082912.gPDpgVy3@linutronix.de>
 <20240529103409.3iiemroaavv5lh2p@airbuntu>
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On 2024-05-29 11:34:09 [+0100], Qais Yousef wrote:
> > behaviour. But then it is insistent which matters only in the RT case.
> > Puh. Any sched folks regarding policy?
> 
> I am not sure I understood you here. Could you rephrase please?

Right now a SCHED_OTHER task boosted to a realtime priority gets
slack=0. In the !RT scenario everything is fine.
For RT the slack=0 also happens but the init of the timer looks at the
policy instead at the possible boosted priority and uses a different
clock attribute. This can lead to a delayed wake up (so avoiding the
slack does not solve the problem).

This is not consistent because IMHO the clock setup & slack should be
handled equally. So I am asking the sched folks for a policy and I am
leaning towards looking at task-policy in this case instead of prio
because you shouldn't do anything that can delay.

Sebastian