Re: [Xen-devel] [PATCH 1/3] xen/sched: populate cpupool0 only after all cpus are up

From: Dario Faggioli <dfaggioli@suse.com>
To: George Dunlap <dunlapg@umich.edu>, Juergen Gross <jgross@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [Xen-devel] [PATCH 1/3] xen/sched: populate cpupool0 only after all cpus are up
Date: Wed, 14 Aug 2019 18:58:56 +0200	[thread overview]
Message-ID: <5996e059f0babfad9f79c1bf535f80dcc68cd14e.camel@suse.com> (raw)
In-Reply-To: <CAFLBxZa=ymiPSQP+Z8_3+6UFnt1eu15Wv5Km-xpShwB=Mpx0MA@mail.gmail.com>

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On Wed, 2019-08-14 at 17:15 +0100, George Dunlap wrote:
> On Fri, Aug 2, 2019 at 2:08 PM Juergen Gross <jgross@suse.com> wrote:
> > --- a/xen/common/cpupool.c
> > +++ b/xen/common/cpupool.c
> > @@ -762,18 +762,28 @@ static struct notifier_block cpu_nfb = {
> >      .notifier_call = cpu_callback
> >  };
> > 
> > -static int __init cpupool_presmp_init(void)
> > +static int __init cpupool_init(void)
> >  {
> > +    unsigned int cpu;
> >      int err;
> > -    void *cpu = (void *)(long)smp_processor_id();
> > +
> >      cpupool0 = cpupool_create(0, 0, &err);
> >      BUG_ON(cpupool0 == NULL);
> >      cpupool_put(cpupool0);
> > -    cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
> >      register_cpu_notifier(&cpu_nfb);
> > +
> > +    spin_lock(&cpupool_lock);
> > +
> > +    cpumask_copy(&cpupool_free_cpus, &cpu_online_map);
> > +
> > +    for_each_cpu ( cpu, &cpupool_free_cpus )
> > +        cpupool_assign_cpu_locked(cpupool0, cpu);
> > +
> > +    spin_unlock(&cpupool_lock);
> 
> Just to make sure I understand what's happening here --
> cpu_callback()
> now won't get called with CPU_ONLINE early in the boot process; but
> it
> will still be called with CPU_ONLINE in other circumstances (e.g.,
> hot-plug / suspend / whatever)?
> 
Exactly.

It is not used for resume (from suspend) any longer, since commit
6870ea9d1fad ("xen/cpupool: simplify suspend/resume handling).

But it is used for putting the various CPUs in Pool-0, as they come-up, 
during boot.

This patch remove the "hack" of calling it directly, during cpupool
initialization, for the BSP.

> Sorry that's an overly-basic question; I don't have a good picture
> for
> the cpu state machine.
> 
Well, I used to... I tried to quickly double check things, and what I
said above should be still valid, even after the latest changes (or so
I hope :-) ).

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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