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

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Message-ID: <CAJWu+oqUSOUrro-Rk-Bg7P6PyCWGKRZVT5i4Bi36XpRRFumL5w@mail.gmail.com>
Date: Wed, 21 Aug 2024 17:41:32 -0400
From: Joel Fernandes <joelaf@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, tj@...nel.org, void@...ifault.com, 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, 
	"Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: Re: [PATCH 0/9] sched: Prepare for sched_ext

On Tue, Aug 13, 2024 at 6:50 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> 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
>

So I booted queue.git sched/core branch on a newish Chromebook (after
applying 700 patches for making it boot and spending 2 days on it
since we boot old kernels -- I wasn't joking when I said I would carve
some time up for you this week :P).

With sched/core , it boots fine with core scheduling disabled, but
when core scheduling is enabled I am getting hard hangs and
occasionally get to the login screen if I'm lucky. So there's
definitely something wonky in sched/core branch and core sched.
I could not get a trace or logs yet, since once it hangs I have to
hard power off.

I could bissect it tomorrow though since it looks like a manageable
set of patches on 6.11-rc1.  Or did you already figure out the issue?

I am based on:
commit aef6987d89544d63a47753cf3741cabff0b5574c
Author: Peter Zijlstra <peterz@...radead.org>
Date:   Thu Jun 20 13:16:49 2024 +0200

    sched/eevdf: Propagate min_slice up the cgroup hierarchy

Thanks,

 - Joel
(++ my open source email)