linux-kernel - Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per runqueue

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <90d1b600-6c95-418d-84af-19604ba9a7d8@intel.com>
Date: Wed, 17 Dec 2025 20:37:07 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Vern Hao <haoxing990@...il.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>, 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>, 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>, Tim Chen
	<tim.c.chen@...ux.intel.com>, Peter Zijlstra <peterz@...radead.org>, "K
 Prateek Nayak" <kprateek.nayak@....com>, "Gautham R . Shenoy"
	<gautham.shenoy@....com>, Vincent Guittot <vincent.guittot@...aro.org>, "Ingo
 Molnar" <mingo@...hat.com>
Subject: Re: [PATCH v2 06/23] sched/cache: Track LLC-preferred tasks per
 runqueue

On 12/17/2025 6:04 PM, Vern Hao wrote:
> 
> On 2025/12/4 07:07, Tim Chen wrote:
>> @@ -1346,8 +1385,13 @@ void account_mm_sched(struct rq *rq, struct 
>> task_struct *p, s64 delta_exec)
>>   #endif
>>       }
>> -    if (p->preferred_llc != mm_sched_llc)
>> +    /* task not on rq accounted later in account_entity_enqueue() */
>> +    if (task_running_on_cpu(rq->cpu, p) &&
>> +        p->preferred_llc != mm_sched_llc) {
>> #ifdef CONFIG_NUMA_BALANCING
>>                  /*
>>                   * Don't assign preferred LLC if it
>>                   * conflicts with NUMA balancing.
>>                   */
>>                  if (p->numa_preferred_nid >= 0 &&
>>                      cpu_to_node(mm->mm_sched_cpu) != p- 
>>  >numa_preferred_nid)
>>                          mm_sched_llc = -1;
>> #endif
>>          }
>> 
>>          /* task not on rq accounted later in account_entity_enqueue() */
>>          if (task_running_on_cpu(rq->cpu, p) &&
>>              p->preferred_llc != mm_sched_llc) {
>>                  account_llc_dequeue(rq, p);
>>                  p->preferred_llc = mm_sched_llc;
>>                  account_llc_enqueue(rq, p);
>> 
>>          }
>> 
> I am a little concerned that there might be cases where both |p- 
>  >preferred_llc| and |mm_sched_llc| are equal to -1 at this point.", Is 
> it necessary to add a check here?
>

Are you concerned about the mismatch between the percpu runqueue values
of nr_pref_llc_running, nr_pref_llc, and nr_llc_running? This should not
be an issue, because account_llc_dequeue() and account_llc_enqueue() are
always invoked together in account_mm_sched(). If p->preferred_llc = 
mm_sched_llc = -1,
account_llc_dequeue/enqueue() will not be invoked, so it is still paired.
Please let me know if I understand your comments correctly.

thanks,
Chenyu