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: <a2c92ba3-4739-4e05-99ac-15078155fca7@intel.com>
Date: Tue, 16 Dec 2025 15:36:24 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>, 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>, 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 12/11/2025 12:52 AM, Peter Zijlstra wrote:
> On Wed, Dec 10, 2025 at 05:32:35PM +0100, Peter Zijlstra wrote:
>> 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?
> 
> Also, patch doesn't use sched_cache_present at all, so perhaps just drop
> it on the floor entirely?

The sched_cache_present flag is used in a subsequent patch:
"[20/23] sched/cache: Add user control to adjust the parameters of 
cache-aware
scheduling" This flag is used to check whether the user is eligible to 
enable
cache-aware scheduling. I will try to place the declaration and usage of 
this
flag together.

thanks,
Chenyu