linux-kernel - Re: [PATCH v2 05/23] sched/cache: Assign preferred LLC ID to processes

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Message-ID: <7dab5ae3-496d-408e-83c8-d5df104b9f87@intel.com>
Date: Wed, 7 Jan 2026 16:38:33 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Jianyong Wu <jianyong.wu@...look.com>, Tim Chen
	<tim.c.chen@...ux.intel.com>
CC: 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>, "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>, Peter Zijlstra
	<peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, K Prateek Nayak
	<kprateek.nayak@....com>, "Gautham R . Shenoy" <gautham.shenoy@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v2 05/23] sched/cache: Assign preferred LLC ID to
 processes

On 1/7/2026 12:49 PM, Jianyong Wu wrote:
> Hi Tim,
> 
> On 12/4/2025 7:07 AM, Tim Chen wrote:
>> +
>> +    if (mm->mm_sched_cpu != -1) {
>> +        mm_sched_llc = llc_id(mm->mm_sched_cpu);
>> +
>> +#ifdef CONFIG_NUMA_BALANCING
>> +        /*
>> +         * Don't assign preferred LLC if it
>> +         * conflicts with NUMA balancing.
>> +         */
>> +        if (p->numa_preferred_nid >= 0 &&
>> +            cpu_to_node(mm->mm_sched_cpu) != p->numa_preferred_nid)
>> +            mm_sched_llc = -1;
> 
> Scenario: NUMA balancing is initially enabled and numa_preferred_nid is 
> set. After disabling NUMA balancing, numa_preferred_nid is not cleared, 
> leading to unintended impact of NUMA balancing on cache-aware 
> scheduling. Should we check if NUMA balancing is disabled before 
> checking numa_preferred_nid?
> 

Good point, sched_numa_balancing should be checked here.

thanks,
Chenyu

> Thanks
> Jianyong Wu
>