linux-kernel - Re: [RFC PATCH 0/2] Disable RT-throttling for idle-inject threads

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Date: Wed, 10 Apr 2024 14:24:14 +0200
From: Daniel Bristot de Oliveira <bristot@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>,
 Atul Kumar Pant <quic_atulpant@...cinc.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, rafael@...nel.org,
 daniel.lezcano@...aro.org, kernel@...cinc.com, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Disable RT-throttling for idle-inject threads

On 4/10/24 13:46, Peter Zijlstra wrote:
> Also, we'll be replacing the throttling code with DL servers 'soonish'
> at which point all this will stop working anyway, since DL will preempt
> anything FIFO, including your idle injection crud.

+1

also, given that the code spins with preempt disabled, with dl server it could
even become a non-rt thread...

FIFO RUNNING
	DL_SERVER activates
		their loop
			disables preemption()
			run()
			enable preemption()
	DL_SERVE throttled
FIFO BACK

So, there will be no need for this busy loop to be RT.

Anyways, it breaks RT and DL if it keeps running for too long... It can
also cause complaints like RCU stalls and loong wait on locks, e.g., on
kworkers...

-- Daniel