linux-kernel - Re: [PATCH v2 04/14] sched_ext: Use per-CPU DSQs instead of per-node global DSQs in bypass mode

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Message-ID: <CABFh=a6GNZSzrLzyonv5aYn8Rh06YquVoGHJfJnYL8rMOymZ+Q@mail.gmail.com>
Date: Mon, 10 Nov 2025 18:26:19 -0500
From: Emil Tsalapatis <linux-lists@...alapatis.com>
To: Tejun Heo <tj@...nel.org>
Cc: David Vernet <void@...ifault.com>, Andrea Righi <andrea.righi@...ux.dev>, 
	Changwoo Min <changwoo@...lia.com>, Dan Schatzberg <schatzberg.dan@...il.com>, 
	Emil Tsalapatis <etsal@...a.com>, sched-ext@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Andrea Righi <arighi@...dia.com>
Subject: Re: [PATCH v2 04/14] sched_ext: Use per-CPU DSQs instead of per-node
 global DSQs in bypass mode

Hi Tejun,

On Mon, Nov 10, 2025 at 4:59 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello, Emil.
>
> On Mon, Nov 10, 2025 at 04:43:23PM -0500, Emil Tsalapatis wrote:
> > > @@ -1298,7 +1298,7 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
> > >
> > >         if (scx_rq_bypassing(rq)) {
> > >                 __scx_add_event(sch, SCX_EV_BYPASS_DISPATCH, 1);
> >
> > Nit: The bypass label has a single statement, and there is no fallthrough to it.
> > Can we just add the logic here:
> >
> > dsq = &task_rq(p)->scx.bypass_dsq;
> > goto enqueue;
> >
> > and remove the new label?
> >
> > > -               goto global;
> > > +               goto bypass;
> > >         }
> > >
> > >         if (p->scx.ddsp_dsq_id != SCX_DSQ_INVALID)
> > > @@ -1356,6 +1356,9 @@ static void do_enqueue_task(struct rq *rq, struct task_struct *p, u64 enq_flags,
> > >  global:
> > >         dsq = find_global_dsq(sch, p);
> > >         goto enqueue;
> > > +bypass:
> > > +       dsq = &task_rq(p)->scx.bypass_dsq;
> >
> > Nit: If we keep the bypass label, we can remove the goto since the
> > label is right below. Otherwise, we could remove it
>
> This is really subjective but I like the fact that the local, global and
> bypass labels look symmetric. It doesn't make any different to compilers and
> I think keeping them so is less likely to trip up people.
>

Ack, makes total sense.

> Thanks.
>
> --
> tejun