linux-kernel - Re: [PATCH v5 0/2] sched: update the rq->avg_idle when a task is moved to an idle CPU

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <885de678-fd46-4a44-ac92-098bdb6b9cfe@arm.com>
Date: Thu, 4 Dec 2025 14:09:26 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Huang Shijie <shijie@...amperecomputing.com>, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org
Cc: patches@...erecomputing.com, cl@...ux.com,
 Shubhang@...amperecomputing.com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, linux-kernel@...r.kernel.org, vschneid@...hat.com,
 vineethr@...ux.ibm.com, kprateek.nayak@....com
Subject: Re: [PATCH v5 0/2] sched: update the rq->avg_idle when a task is
 moved to an idle CPU

On 03.12.25 06:30, Huang Shijie wrote:
> In the newidle balance, the rq->idle_stamp may set to a non-zero value
> if it cannot pull any task.
> 
> In the wakeup, it will detect the rq->idle_stamp, and updates
> the rq->avg_idle, then ends the CPU idle status by setting rq->idle_stamp
> to zero.
> 
> Besides the wakeup, current code does not end the CPU idle status
> when a task is moved to the idle CPU, such as fork/clone, execve,
> or other cases.

Is there a case which is the most important one? (e.g. idle load balancing)?

I still can't see the reason why this code should be changed (was asked
in v4 already).

Do you have a workload on your machine which gives you better scores in
case you set 'rq->idle_stamp = 0' in all those cases?

What is is actual issue in the current code?

Does 'this_rq->avg_idle' get too big so you spend too much useless time
(since pulled_task == 0) in sched_balance_newidle() because the bailout
condition:

sched_balance_newidle()

  ...
  if (!get_rd_overloaded(this_rq->rd) ||
      this_rq->avg_idle < sd->max_newidle_lb_cost) {
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

    ...
    goto out;

doesn't trigger anymore?

[...]