linux-kernel - Re: [PATCH 2/2] sched/dlserver: fix dlserver time accounting

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Message-ID: <41be49a210d5ef1c48cd0cbfe23a52368cb049b9.camel@codethink.co.uk>
Date: Fri, 13 Dec 2024 11:10:52 +0100
From: Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk>
To: "Vineeth Pillai (Google)" <vineeth@...byteword.org>, Peter Zijlstra
	 <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Vincent Guittot
 <vincent.guittot@...aro.org>,  Joel Fernandes <joel@...lfernandes.org>,
 shraash@...gle.com, i.maximets@....org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/dlserver: fix dlserver time accounting

Thank you very much, Vineeth

On Thu, 2024-12-12 at 22:22 -0500, Vineeth Pillai (Google) wrote:
> dlserver time is accounted when:
> - dlserver is active and the dlserver proxies the cfs task.
> - dlserver is active but deferred and cfs task runs after being picked
>   through the normal fair class pick.
> 
> dl_server_update is called in two places to make sure that both the
> above times are accounted for. But it doesn't check if dlserver is
> active or not. Now that we have this dl_server_active flag, we can
> consolidate dl_server_update into one place and all we need to check is
> whether dlserver is active or not. When dlserver is active there is only
> two possible conditions:
> - dlserver is deferred.
> - cfs task is running on behalf of dlserver.
> 
> Signed-off-by: Vineeth Pillai (Google) <vineeth@...byteword.org>

Tested-by: Marcel Ziswiler <marcel.ziswiler@...ethink.co.uk> # ROCK 5B

> ---
>  kernel/sched/fair.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 2d80aaac4413..f5329672815b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1159,8 +1159,6 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec)
>  	trace_sched_stat_runtime(p, delta_exec);
>  	account_group_exec_runtime(p, delta_exec);
>  	cgroup_account_cputime(p, delta_exec);
> -	if (p->dl_server)
> -		dl_server_update(p->dl_server, delta_exec);
>  }
>  
>  static inline bool did_preempt_short(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> @@ -1237,11 +1235,16 @@ static void update_curr(struct cfs_rq *cfs_rq)
>  		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 possibly avoid running this period.
> +		 * If the fair_server is active, we need to account for the
> +		 * fair_server time whether or not the task is running on
> +		 * behalf of fair_server or not:
> +		 *  - If the task is running on behalf of fair_server, we need
> +		 *    to limit its time based on the assigned runtime.
> +		 *  - Fair task that runs outside of fair_server should account
> +		 *    against fair_server such that it can account for this time
> +		 *    and possibly avoid running this period.
>  		 */
> -		if (p->dl_server != &rq->fair_server)
> +		if (dl_server_active(&rq->fair_server))
>  			dl_server_update(&rq->fair_server, delta_exec);
>  	}

Cheers

Marcel