linux-kernel - Re: [PATCH v2 16/23] sched/cache: Introduce sched_cache_present to enable cache aware scheduling for multi LLCs NUMA node

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Message-ID: <20251210163235.GX3707891@noisy.programming.kicks-ass.net>
Date: Wed, 10 Dec 2025 17:32:35 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Chen Yu <yu.c.chen@...el.com>, Juri Lelli <juri.lelli@...hat.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
	Hillf Danton <hdanton@...a.com>,
	Shrikanth Hegde <sshegde@...ux.ibm.com>,
	Jianyong Wu <jianyong.wu@...look.com>,
	Yangyu Chen <cyy@...self.name>,
	Tingyin Duan <tingyin.duan@...il.com>,
	Vern Hao <vernhao@...cent.com>, Vern Hao <haoxing990@...il.com>,
	Len Brown <len.brown@...el.com>, Aubrey Li <aubrey.li@...el.com>,
	Zhao Liu <zhao1.liu@...el.com>, Chen Yu <yu.chen.surf@...il.com>,
	Adam Li <adamli@...amperecomputing.com>,
	Aaron Lu <ziqianlu@...edance.com>, Tim Chen <tim.c.chen@...el.com>,
	linux-kernel@...r.kernel.org, Libo Chen <libo.chen@...cle.com>
Subject: Re: [PATCH v2 16/23] sched/cache: Introduce sched_cache_present to
 enable cache aware scheduling for multi LLCs NUMA node

On Wed, Dec 03, 2025 at 03:07:35PM -0800, Tim Chen wrote:
> From: Chen Yu <yu.c.chen@...el.com>
> 
> Cache-aware load balancing should only be enabled if there are more
> than 1 LLCs within 1 NUMA node. sched_cache_present is introduced to
> indicate whether this platform supports this topology.
> 
> Suggested-by: Libo Chen <libo.chen@...cle.com>
> Suggested-by: Adam Li <adamli@...amperecomputing.com>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> ---
> 
> Notes:
>     v1->v2:
>     	Use flag sched_cache_present to indicate whether a platform
>     	supports cache aware scheduling. Change this flag from staic key.
>     	There should be only 1 static key to control the cache aware
>     	scheduling. (Peter Zijlstra)
> 
>  kernel/sched/topology.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index d583399fc6a1..9799e3a9a609 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -24,6 +24,8 @@ int max_llcs;
>  
>  #ifdef CONFIG_SCHED_CACHE
>  
> +static bool sched_cache_present;

sched_energy_present
sched_asym_cpucapacity
sched_cluster_active
sched_smt_present

are all static keys tied to the current topology, why break the streak
and make this a boolean?