linux-kernel - Re: [RFC PATCH v3 06/10] sched/fair: Prepare switched_from & switched

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240712152641.GT27299@noisy.programming.kicks-ass.net>
Date: Fri, 12 Jul 2024 17:26:41 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Valentin Schneider <vschneid@...hat.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Phil Auld <pauld@...hat.com>, Clark Williams <williams@...hat.com>,
	Tomas Glozar <tglozar@...hat.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Arnd Bergmann <arnd@...db.de>, Guo Ren <guoren@...nel.org>,
	Palmer Dabbelt <palmer@...osinc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC PATCH v3 06/10] sched/fair: Prepare switched_from &
 switched_to for per-task throttling

On Thu, Jul 11, 2024 at 03:00:00PM +0200, Valentin Schneider wrote:
> Later commits will change CFS bandwidth control throttling from a
> per-cfs_rq basis to a per-task basis. This means special care needs to be
> taken around any transition a task can have into and out of a cfs_rq.
> 
> To ease reviewing, the transitions are patched with dummy-helpers that are
> implemented later on.
> 
> Add helpers to switched_from_fair() and switched_to_fair() to cover class
> changes. If switching from CFS, a task may need to be unthrottled. If
> switching to CFS, a task may need to be throttled.
> 
> Signed-off-by: Valentin Schneider <vschneid@...hat.com>
> ---
>  kernel/sched/fair.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 095357bd17f0e..acac0829c71f3 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5694,6 +5694,10 @@ static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
>  	return cfs_bandwidth_used() && cfs_rq->throttle_count;
>  }
>  
> +static inline bool task_needs_throttling(struct task_struct *p) { return false; }
> +static inline void task_throttle_setup(struct task_struct *p) { }
> +static inline void task_throttle_cancel(struct task_struct *p) { }
> +
>  /*
>   * Ensure that neither of the group entities corresponding to src_cpu or
>   * dest_cpu are members of a throttled hierarchy when performing group
> @@ -6622,6 +6626,10 @@ static inline int throttled_lb_pair(struct task_group *tg,
>  	return 0;
>  }
>  
> +static inline bool task_needs_throttling(struct task_struct *p) { return false; }
> +static inline void task_throttle_setup(struct task_struct *p) { }
> +static inline void task_throttle_cancel(struct task_struct *p) { }
> +
>  #ifdef CONFIG_FAIR_GROUP_SCHED
>  void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b, struct cfs_bandwidth *parent) {}
>  static void init_cfs_rq_runtime(struct cfs_rq *cfs_rq) {}
> @@ -12847,11 +12855,15 @@ static void attach_task_cfs_rq(struct task_struct *p)
>  static void switched_from_fair(struct rq *rq, struct task_struct *p)
>  {
>  	detach_task_cfs_rq(p);
> +	if (cfs_bandwidth_used())
> +		task_throttle_cancel(p);
>  }
>  
>  static void switched_to_fair(struct rq *rq, struct task_struct *p)
>  {
>  	attach_task_cfs_rq(p);
> +	if (cfs_bandwidth_used() && task_needs_throttling(p))
> +		task_throttle_setup(p);
>  
>  	set_task_max_allowed_capacity(p);

Other functions seem to have cfs_bandwidth_used() inside them, and not
bother the caller with this detail.