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: <tencent_745BD89104F736A63D04B0D18F8F52104505@qq.com>
Date: Fri, 19 Dec 2025 22:48:36 +0800
From: Yangyu Chen <cyy@...self.name>
To: "Chen, Yu C" <yu.c.chen@...el.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>,
 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 19 Dec 2025, at 22:41, Chen, Yu C <yu.c.chen@...el.com> wrote:
> 
> 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?

It requires debugfs being mounted with enough permissions. It’s not
feasible for normal user-space software without root permission.

Thanks,
Yangyu Chen

> 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