linux-kernel - Re: [RFC PATCH v4 08/28] sched: Set up LLC indexing

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Message-ID: <86fb463f-19bd-4242-8217-4d0f9e852c07@intel.com>
Date: Tue, 30 Sep 2025 10:54:01 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Adam Li <adamli@...amperecomputing.com>
CC: 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>, Libo Chen
	<libo.chen@...cle.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>, Len
 Brown <len.brown@...el.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Aubrey Li
	<aubrey.li@...el.com>, Zhao Liu <zhao1.liu@...el.com>, Chen Yu
	<yu.chen.surf@...il.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>
Subject: Re: [RFC PATCH v4 08/28] sched: Set up LLC indexing

On 9/29/2025 6:43 PM, Adam Li wrote:
> On 9/26/2025 9:51 PM, Chen, Yu C wrote:
>> Hi Adam,
>>
>> On 9/26/2025 2:14 PM, Adam Li wrote:

[snip]
>>>    #ifdef CONFIG_SCHED_CACHE
>>> -       if (llc_has_parent_sd && multi_llcs_node && !sched_asym_cpucap_active())
>>> +       if (has_llc && llc_has_parent_sd && multi_llcs_node &&
>>
>> multi_llcs_node will be false if there is no SD_SHARE_LLC domain on the
>> platform, so I suppose we don’t have to introduce has_llc?
>> multi_llcs is set to true iff there are more than 1 SD_SHARE_LLC domains under its
>> SD_SHARE_LLC parent domain.
>>
> 
> If there is *no* SD_SHARE_LLC domain, my test shows 'multi_llcs_node' is still 1 (true).
> 
> Looks it is because the default value of 'multi_llcs_node' is 1.
> 
> build_sched_domains():
> 	unsigned int multi_llcs_node = 1;
> 
> And this condition is always false since we have no SD_SHARE_LLC domain,
> therefore 'multi_llcs_node' will not be changed:
> 
>                          if (!(sd->flags & SD_SHARE_LLC) && child &&
>                              (child->flags & SD_SHARE_LLC))
> 

I see. I was looking at the v5 internal version where
multi_llcs was initialized to 0. Let me double check
and refine the logic. Thanks!

Chenyu


> Thanks,
> -adam