linux-kernel - [PATCH 0/9] sched: Prepare for sched

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Message-Id: <20240813222548.049744955@infradead.org>
Date: Wed, 14 Aug 2024 00:25:48 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org,
 tj@...nel.org,
 void@...ifault.com
Cc: peterz@...radead.org,
 juri.lelli@...hat.com,
 vincent.guittot@...aro.org,
 dietmar.eggemann@....com,
 rostedt@...dmis.org,
 bsegall@...gle.com,
 mgorman@...e.de,
 vschneid@...hat.com,
 linux-kernel@...r.kernel.org,
 joelaf@...gle.com
Subject: [PATCH 0/9] sched: Prepare for sched_ext

Hi,

These patches apply on top of the EEVDF series (queue/sched/core), which
re-arranges the fair pick_task() functions to make them state invariant such
that they can easily be restarted upon picking (and dequeueing) a delayed task.

This same is required to push (the final) put_prev_task() beyond pick_task(),
like we do for sched_core already.

This in turn is done to prepare for sched_ext, which wants a final callback to
be in possesion of the next task, such that it can tell if the context switch
will leave the sched_class.

As such, this all re-arranges the current order of:

  put_prev_task(rq, prev);
  next = pick_next_task(rq); /* implies set_next_task(.first=true); */

to sometihng like:

  next = pick_task(rq)
  if (next != prev) {
    put_prev_task(rq, prev, next);
    set_next_task(rq, next, true);
  }

The patches do a fair bit of cleaning up. Notably a bunch of sched_core stuff
-- Joel, could you please test this stuff, because the self-tests we have are
hardly adequate.

The EEVDF stuff was supposed to be merged already, but since Valentin seems to
be doing a read-through, I figured I'd give him a little extra time. A complete
set can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/prep