linux-kernel - Re: [PATCH 04/19] sched/fair: Introduce a static key to enable cache aware only for multi LLCs

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Message-ID: <20251016074227.GY3289052@noisy.programming.kicks-ass.net>
Date: Thu, 16 Oct 2025 09:42:27 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Chen, Yu C" <yu.c.chen@...el.com>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, Ingo Molnar <mingo@...hat.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	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>,
	Jianyong Wu <jianyong.wu@...look.com>,
	Yangyu Chen <cyy@...self.name>,
	Tingyin Duan <tingyin.duan@...il.com>,
	Vern Hao <vernhao@...cent.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>,
	Tim Chen <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
	Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH 04/19] sched/fair: Introduce a static key to enable cache
 aware only for multi LLCs

On Thu, Oct 16, 2025 at 01:01:05AM +0800, Chen, Yu C wrote:

> Oh, do you mean only using sched_cache_allowed in sched_cache_enabled()?
> I misunderstood that Peter suggested introducing only one key. But I didn't
> quite catch up - do you mean we should monitor the switch of FEAT, modify
> sched_cache_allowed when needed, and that the OS only queries
> sched_cache_allowed
> at runtime?

Just don't use sched_feat(), add a debugfs file like numa_balancing and
then combine the userspace and topology information when setting the one
static_branch.