linux-kernel - Re: [PATCH] sched/rt: Clean up usage of rt

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Message-ID: <20240515103118.qc76v55x4ylqhd52@airbuntu>
Date: Wed, 15 May 2024 11:31:18 +0100
From: Qais Yousef <qyousef@...alina.io>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Phil Auld <pauld@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] sched/rt: Clean up usage of rt_task()

On 05/15/24 10:32, Peter Zijlstra wrote:
> On Tue, May 14, 2024 at 07:58:51PM -0400, Phil Auld wrote:
> > 
> > Hi Qais,
> > 
> > On Wed, May 15, 2024 at 12:41:12AM +0100 Qais Yousef wrote:
> > > rt_task() checks if a task has RT priority. But depends on your
> > > dictionary, this could mean it belongs to RT class, or is a 'realtime'
> > > task, which includes RT and DL classes.
> > > 
> > > Since this has caused some confusion already on discussion [1], it
> > > seemed a clean up is due.
> > > 
> > > I define the usage of rt_task() to be tasks that belong to RT class.
> > > Make sure that it returns true only for RT class and audit the users and
> > > replace them with the new realtime_task() which returns true for RT and
> > > DL classes - the old behavior. Introduce similar realtime_prio() to
> > > create similar distinction to rt_prio() and update the users.
> > 
> > I think making the difference clear is good. However, I think rt_task() is
> > a better name. We have dl_task() still.  And rt tasks are things managed
> > by rt.c, basically. Not realtime.c :)  I know that doesn't work for deadline.c
> > and dl_ but this change would be the reverse of that pattern.
> 
> It's going to be a mess either way around, but I think rt_task() and
> dl_task() being distinct is more sensible than the current overlap.

Judging by some of the users I've seen, I think there were some users not
expecting they're not distinct as they were checking for !dl_task() &&
!rt_task() which I replaced with !realtime_task(). Similar users checking for
dl_prio() and rt_prio() in places, and others using rt_prio() to encompass
dl_prio(). There were BUG_ON(!rt_task())/WARN_ON(!rt_prio()) in rt.c which
I don't think it in intended to encompass dl there.

> 
> > > Move MAX_DL_PRIO to prio.h so it can be used in the new definitions.
> > > 
> > > Document the functions to make it more obvious what is the difference
> > > between them. PI-boosted tasks is a factor that must be taken into
> > > account when choosing which function to use.
> > > 
> > > Rename task_is_realtime() to task_has_realtime_policy() as the old name
> > > is confusing against the new realtime_task().
> 
> realtime_task_policy() perhaps?

Better yes. Updated.

Thanks!