linux-kernel - Re: [PATCH v6 01/20] sched: Unify runtime accounting across classes

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Date: Sun, 17 Dec 2023 16:19:27 +0000
From: Qais Yousef <qyousef@...alina.io>
To: John Stultz <jstultz@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Joel Fernandes <joelaf@...gle.com>,
	Qais Yousef <qyousef@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...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>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	"Paul E . McKenney" <paulmck@...nel.org>, kernel-team@...roid.com,
	Connor O'Brien <connoro@...gle.com>
Subject: Re: [PATCH v6 01/20] sched: Unify runtime accounting across classes

On 11/06/23 19:34, John Stultz wrote:
> From: Peter Zijlstra <peterz@...radead.org>
> 
> All classes use sched_entity::exec_start to track runtime and have
> copies of the exact same code around to compute runtime.
> 
> Collapse all that.
> 
> Cc: Joel Fernandes <joelaf@...gle.com>
> Cc: Qais Yousef <qyousef@...gle.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@....com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ben Segall <bsegall@...gle.com>
> Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
> Cc: Youssef Esmat <youssefesmat@...gle.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: "Paul E . McKenney" <paulmck@...nel.org>
> Cc: kernel-team@...roid.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> [fix conflicts, fold in update_current_exec_runtime]
> Signed-off-by: Connor O'Brien <connoro@...gle.com>
> [jstultz: rebased, resovling minor conflicts]
> Signed-off-by: John Stultz <jstultz@...gle.com>
> ---
> NOTE: This patch is a general cleanup and if no one objects
> could be merged at this point. If needed, I'll resend separately
> if it isn't picked up on its own.

Looks like this actually got merged into tip via the deadline server work :-)

Though not sure if I caught a bug here

> diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> index 85590599b4d6..7595494ceb6d 100644
> --- a/kernel/sched/stop_task.c
> +++ b/kernel/sched/stop_task.c
> @@ -70,18 +70,7 @@ static void yield_task_stop(struct rq *rq)
>  
>  static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
>  {
> -	struct task_struct *curr = rq->curr;
> -	u64 now, delta_exec;
> -
> -	now = rq_clock_task(rq);
> -	delta_exec = now - curr->se.exec_start;
> -	if (unlikely((s64)delta_exec < 0))
> -		delta_exec = 0;

If negative instead of returning for stopper task; we set delta_exec to 0

> -
> -	schedstat_set(curr->stats.exec_max,
> -		      max(curr->stats.exec_max, delta_exec));
> -
> -	update_current_exec_runtime(curr, now, delta_exec);

And curry on to do time accounting

> +	update_curr_common(rq);

But the new function will return early without doing accounting. Wouldn't this
re-introrduce 8f6189684eb4 ("sched: Fix migration thread runtime bogosity")?

>  }


Cheers

--
Qais Yousef