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Date:   Mon, 6 Nov 2023 15:55:19 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Daniel Bristot de Oliveira <bristot@kernel.org>
Cc:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        linux-kernel@vger.kernel.org,
        Luca Abeni <luca.abeni@santannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
        Thomas Gleixner <tglx@linutronix.de>,
        Joel Fernandes <joel@joelfernandes.org>,
        Vineeth Pillai <vineeth@bitbyteword.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Phil Auld <pauld@redhat.com>
Subject: Re: [PATCH v5 6/7] sched/deadline: Deferrable dl server
Message-ID: <20231106145519.GG3818@noisy.programming.kicks-ass.net>
References: <cover.1699095159.git.bristot@kernel.org>
 <c7b706d30d6316c52853ca056db5beb82ba72863.1699095159.git.bristot@kernel.org>
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On Sat, Nov 04, 2023 at 11:59:23AM +0100, Daniel Bristot de Oliveira wrote:

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index b15f7f376a67..399237cd9f59 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1201,6 +1201,8 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  		account_group_exec_runtime(curtask, delta_exec);
>  		if (curtask->server)
>  			dl_server_update(curtask->server, delta_exec);
> +		else
> +			dl_server_update(&rq_of(cfs_rq)->fair_server, delta_exec);
>  	}
>  
>  	account_cfs_rq_runtime(cfs_rq, delta_exec);

I've rewritten that something like so..

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1182,12 +1182,13 @@ s64 update_curr_common(struct rq *rq)
 static void update_curr(struct cfs_rq *cfs_rq)
 {
 	struct sched_entity *curr = cfs_rq->curr;
+	struct rq *rq = rq_of(cfs_rq);
 	s64 delta_exec;
 
 	if (unlikely(!curr))
 		return;
 
-	delta_exec = update_curr_se(rq_of(cfs_rq), curr);
+	delta_exec = update_curr_se(rq, curr);
 	if (unlikely(delta_exec <= 0))
 		return;
 
@@ -1195,8 +1196,17 @@ static void update_curr(struct cfs_rq *c
 	update_deadline(cfs_rq, curr);
 	update_min_vruntime(cfs_rq);
 
-	if (entity_is_task(curr))
-		update_curr_task(task_of(curr), delta_exec);
+	if (entity_is_task(curr)) {
+		struct task_struct *p = task_of(curr);
+		update_curr_task(p, delta_exec);
+		/*
+		 * Any fair task that runs outside of fair_server should
+		 * account against fair_server such that it can account for
+		 * this time and possible avoid running this period.
+		 */
+		if (p->dl_server != &rq->fair_server)
+			dl_server_update(&rq->fair_server, delta_exec);
+	}
 
 	account_cfs_rq_runtime(cfs_rq, delta_exec);
 }