linux-kernel - Re: [PATCH v2 21/23] -- DO NOT APPLY!!! -- sched/cache/stats: Add schedstat for cache aware load balancing

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Message-ID: <c3d765f6-46e2-4158-bc61-e10bad134789@intel.com>
Date: Fri, 19 Dec 2025 22:41:28 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Yangyu Chen <cyy@...self.name>, Tim Chen <tim.c.chen@...ux.intel.com>
CC: 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>, "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>, 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>
Subject: Re: [PATCH v2 21/23] -- DO NOT APPLY!!! -- sched/cache/stats: Add
 schedstat for cache aware load balancing

On 12/19/2025 1:03 PM, Yangyu Chen wrote:
> 
>> On 4 Dec 2025, at 07:07, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
>>
>> From: Chen Yu <yu.c.chen@...el.com>
>>
>> Debug patch only.
>>
>> With cache-aware load balancing enabled, statistics related to its activity
>> are exposed via /proc/schedstat and debugfs. For instance, if users want to
>> verify metrics like the number of exceeding RSS and nr_running limits, they
>> can filter the output of /sys/kernel/debug/sched/debug and compute the required
>> statistics manually:
>>
>> llc_exceed_cap SUM: 6
>> llc_exceed_nr SUM: 4531
>>
>> Furthermore, these statistics exposed in /proc/schedstats can be queried manually
>> or via perf sched stats[1] with minor modifications.
>>
> 
> Hi Tim,
> 
> This patch looks great, especially for multithread Verilator workloads
> on clustered LLC (like AMD EPYC). I'm discussing with Verilator
> upstream to disable automatic userspace affinity assignment in
> Verilator if such feature exist [1]. During the discussion, I think
> there should be a way for userspace software to detect if such a
> feature exists. Could we expose it in `/proc/schedstats` to allow
> userspace software to detect such a feature? We can just use this
> patch and remove the "DO NOT APPLY" tag.
> 

Thanks for the test Yangyu. Does /sys/kernel/debug/sched/llc_enabled
work for you?
Anyway we can try to include /proc/schedstats as the formal one
in the next version.

Thanks,
Chenyu

> [1] https://github.com/verilator/verilator/issues/6826#issuecomment-3671287551
> 
> Thanks,
> Yangyu Chen
> 

>