Re: Null scheduler and vwfi native problem

[Anders Törnqvist <anders.tornqvist@xxxxxxxxx>]

On 1/22/21 3:02 PM, Julien Grall wrote:
> Hi Dario,
>
> On 21/01/2021 23:35, Dario Faggioli wrote:
> > On Thu, 2021-01-21 at 19:40 +0000, Julien Grall wrote:
> > > Hi Dario,
> > Hi!
> >
> > > On 21/01/2021 18:32, Dario Faggioli wrote:
> > > > On Thu, 2021-01-21 at 11:54 +0100, Anders Törnqvist wrote:
> > > > > https://lists.xenproject.org/archives/html/xen-devel/2018-09/msg01213.html
> > > > > .
> > > > Right. Back then, PCI passthrough was involved, if I remember
> > > > correctly. Is it the case for you as well?
> > > PCI passthrough is not yet supported on Arm :). However, the bug was
> > > reported with platform device passthrough.
> > Yeah, well... That! Which indeed is not PCI. Sorry for the terminology
> > mismatch. :-)
> >
> > > > Well, I'll think about it. >
> > > > > Starting the system without "sched=null vwfi=native" does not
> > > > > result
> > > > > in
> > > > > the problem.
> > > > Ok, how about, if you're up for some more testing:
> > > >
> > > >    - booting with "sched=null" but not with "vwfi=native"
> > > >    - booting with "sched=null vwfi=native" but not doing the IRQ
> > > >      passthrough that you mentioned above
> > > >
> > > > ?
> > > I think we can skip the testing as the bug was fully diagnostics back
> > > then. Unfortunately, I don't think a patch was ever posted.
> > True. But an hackish debug patch was provided and, back then, it
> > worked.
> >
> > OTOH, Anders seems to be reporting that such a patch did not work here.
> > I also continue to think that we're facing the same or a very similar
> > problem... But I'm curious why applying the patch did not help this
> > time. And that's why I asked for more testing.
> I wonder if this is because your patch doesn't modify rsinterval. So 
> even if we call force_quiescent_state(), the softirq would only be 
> raised for the current CPU.
> I guess the following HACK could confirm the theory:
>
> diff --git a/xen/common/rcupdate.c b/xen/common/rcupdate.c
> index a5a27af3def0..50020bc34ddf 100644
> --- a/xen/common/rcupdate.c
> +++ b/xen/common/rcupdate.c
> @@ -250,7 +250,7 @@ static void force_quiescent_state(struct rcu_data 
> *rdp,
>  {
>      cpumask_t cpumask;
>      raise_softirq(RCU_SOFTIRQ);
> -    if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
> +    if (1 || unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
>          rdp->last_rs_qlen = rdp->qlen;
>          /*
>           * Don't send IPI to itself. With irqs disabled,
>
> Cheers,
I applied the patch above. No change. The function 
complete_domain_destroy function is not call when I destroy the domain.
/Anders