linux-kernel - Re: [RFC patch v3 02/20] sched: Several fixes for cache aware scheduling

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Message-ID: <7aff826a-87b4-43e8-9b15-19ea5f043d16@oracle.com>
Date: Tue, 8 Jul 2025 08:47:37 -0700
From: Libo Chen <libo.chen@...cle.com>
To: "Chen, Yu C" <yu.c.chen@...el.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>,
        Tim Chen <tim.c.chen@...el.com>,
        Vincent Guittot
 <vincent.guittot@...aro.org>,
        Abel Wu <wuyun.abel@...edance.com>,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>,
        Hillf Danton <hdanton@...a.com>, Len Brown <len.brown@...el.com>,
        linux-kernel@...r.kernel.org, Tim Chen <tim.c.chen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>
Subject: Re: [RFC patch v3 02/20] sched: Several fixes for cache aware
 scheduling



On 7/8/25 00:54, Chen, Yu C wrote:
> On 7/8/2025 9:15 AM, Libo Chen wrote:
>> Hi Chenyu
>>
>> On 6/18/25 11:27, Tim Chen wrote:
>>> From: Chen Yu <yu.c.chen@...el.com>
>>>
>>> 1. Fix compile error on percpu allocation.
>>> 2. Enqueue to the target CPU rather than the current CPU.
>>> 3. NULL LLC sched domain check(Libo Chen).
>>
>> Can I suggest we completely disable cache-aware scheduling
>> for systems without any LLC in the next version? No more added
>> fields, function code for them. This info should be easily
>> determinable during bootup while building up the topology,
>> and cannot be modified during runtime. Sometimes it's not
>> possible for distros to disable it in kconfig just for one
>> particular CPU, and SCHED_CACHE_LB isn't enough for removing
>> the added fields and users can turn it back on anyway.
>>
> 
> Good point, my understanding is that we should introduce
> a static key similar to sched_smt_present to get rid of the
Exactly!
> cache-aware scheduling code path if either LLC is not present
> or there is only 1 LLC within the Node.
> 
> Thanks,
> Chenyu
> 
>> Thanks,
>> Libo
>>
>>
>