linux-kernel - Re: [PATCH v11 7/7] sched: Split scheduler and execution contexts

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Message-ID: <20240731143635.GB188529@pauld.westford.csb>
Date: Wed, 31 Jul 2024 10:36:35 -0400
From: Phil Auld <pauld@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>, John Stultz <jstultz@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Joel Fernandes <joelaf@...gle.com>,
	Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Valentin Schneider <vschneid@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Zimuzo Ezeozue <zezeozue@...gle.com>,
	Youssef Esmat <youssefesmat@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Xuewen Yan <xuewen.yan94@...il.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Metin Kaya <Metin.Kaya@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>, kernel-team@...roid.com,
	Connor O'Brien <connoro@...gle.com>
Subject: Re: [PATCH v11 7/7] sched: Split scheduler and execution contexts

On Wed, Jul 31, 2024 at 01:37:20PM +0200 Peter Zijlstra wrote:
> 
> Sorry for the delay, I need the earth to stop spinning so goddamn fast
> :-) 36 hours days ftw or so... Oh wait, that'd mean other people also
> increase the amount of crap they send my way, don't it?
> 
> Damn..
> 
> On Wed, Jul 31, 2024 at 11:11:45AM +0200, Juri Lelli wrote:
> > Hi John,
> > 
> > On 12/07/24 12:10, John Stultz wrote:
> > > On Fri, Jul 12, 2024 at 8:02 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > On Tue, Jul 09, 2024 at 01:31:50PM -0700, John Stultz wrote:
> > > > > From: Peter Zijlstra <peterz@...radead.org>
> > > > >
> > > > > Let's define the scheduling context as all the scheduler state
> > > > > in task_struct for the task selected to run, and the execution
> > > > > context as all state required to actually run the task.
> > > > >
> > > > > Currently both are intertwined in task_struct. We want to
> > > > > logically split these such that we can use the scheduling
> > > > > context of the task selected to be scheduled, but use the
> > > > > execution context of a different task to actually be run.
> > > > >
> > > > > To this purpose, introduce rq_selected() macro to point to the
> > > > > task_struct selected from the runqueue by the scheduler, and
> > > > > will be used for scheduler state, and preserve rq->curr to
> > > > > indicate the execution context of the task that will actually be
> > > > > run.
> > > >
> > > > > * Swapped proxy for selected for clarity
> > > >
> > > > I'm not loving this naming...  what does selected even mean? What was
> > > > wrong with proxy? -- (did we have this conversation before?)
> > > 
> > > So yeah, this came up earlier:
> > > https://lore.kernel.org/lkml/CANDhNCr3acrEpBYd2LVkY3At=HCDZxGWqbMMwzVJ-Mn--dv3DA@mail.gmail.com/
> > > 
> > > My big concern is that the way proxy was used early in the series
> > > seemed to be inverted from how the term is commonly used.
> > > 
> > > A proxy is one who takes an action on behalf of someone else.
> 
> Ah, I see your confusion.
> 
> > > In this case we have a blocked task that was picked to run, but then
> > > we run another task in its place. Intuitively, this makes the proxy
> > > the one that actually runs, not the one that was picked. But the
> > > earliest versions of the patch had this flipped, and caused lots of
> > > conceptual confusion in the discussions I had with folks about what
> > > the patch was doing (as well as my own confusion initially working on
> > > the patch).
> > 
> > I don't think I have strong preferences either way, but I actually
> > considered the proxy to be the blocked donor (the one picked by the
> > scheduler to run), as it makes the owner use its properties, acting as a
> > proxy for the owner.
> 
> This. But I suspect we both suffer from not being native English
> speakers.
> 
> Would 'donor' work in this case?
>
> Then the donor gets all the accounting done on it, while we execute
> curr.
> 

"donor" works for me and is more expressive (and shorter) than
"selected". Fwiw.



Cheers,
Phil

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