linux-kernel - Re: [RFC PATCH] sched/deadline: Avoid dl_server boosting with expired deadline

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Message-ID: <20251031154455.GU3245006@noisy.programming.kicks-ass.net>
Date: Fri, 31 Oct 2025 16:44:55 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Clark Williams <williams@...hat.com>, arighi@...dia.com
Subject: Re: [RFC PATCH] sched/deadline: Avoid dl_server boosting with
 expired deadline

On Fri, Oct 31, 2025 at 04:41:22PM +0100, Gabriele Monaco wrote:

> > Humm, let me noodle a bit more on this. Also, I should see if I can get
> > graphviz to draw ascii art state diagrams :-)
> 
> Dot doesn't do it but graph-easy does reasonably well.

yep, just found that. Seems to work well:


                          +----------------------+
                          |        A:init        | <+
                          +----------------------+  |
                            |                       |
                            | 1:dl_server_start     | 4:pick_task_dl
                            v                       |
    2:update_curr_dl_se   +----------------------+  |
  +---------------------- |                      |  |
  |                       |  B:zero_laxity-wait  |  |
  +---------------------> |                      | <+------------------+
                          +----------------------+  |                  |
                            |                       |                  |
                            | 3:dl_server_timer     |                  |
                            v                       |                  |
                          +----------------------+  |                  |
  +---------------------> |      C:running       | -+                  | 2:update_curr_dl_se
  |                       +----------------------+                     |
  |                         |                                          |
  | 6:dl_server_timer       | 5:update_curr_dl_se                      |
  |                         v                                          |
  |                       +----------------------+                     |
  +---------------------- |     D:replenish      | --------------------+
                          +----------------------+

Anyway, back to noodling on how to make it stop on idle :-)