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

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Message-ID: <CAJWu+opjcGs8vs9=NcgSU_nuWZE+z73rMaOO7s7OX_=AHvSOiQ@mail.gmail.com>
Date: Thu, 22 Aug 2024 08:58:26 -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 Wed, Aug 21, 2024 at 5:41 PM Joel Fernandes <joelaf@...gle.com> wrote:
>
> 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

One of these 29 in sched/core broke core-scheduling, causes hangs.
Haven't narrowed it down to which. Not much time today. Will probably
try to collect some logs.
https://hastebin.com/share/uqubojiqiy.yaml

Also I realized I should apply the 9 in this set too. But very least
it appears the above 29 broke core-sched vs bissection, probably the
delayed-dequeue or task-pick rework?

I will try the sched/prep branch now, which has the 9 in this set too..

 thanks,

 - Joel