Re: Null scheduler and vwfi native problem

[Julien Grall <julien@xxxxxxx>]

Hi Juergen,

On 03/02/2021 11:00, Jürgen Groß wrote:
> On 03.02.21 10:19, Julien Grall wrote:
> > Hi,
> >
> > On 03/02/2021 07:31, Dario Faggioli wrote:
> > > On Tue, 2021-02-02 at 15:23 +0000, Julien Grall wrote:
> > > > In reality, it is probably still too early as a pCPU can be
> > > > considered
> > > > quiesced until a call to rcu_lock*() (such rcu_lock_domain()).
> > > Well, yes, in theory, we could track down which is the first RCU read
> > > side crit. section on this path, and put the call right before that (if
> > > I understood what you mean).
> > Oh, that's not what I meant. This will indeed be far more complex than 
> > I originally had in mind.
> > AFAIU, the RCU uses critical section to protect data. So the 
> > "entering" could be used as "the pCPU is not quiesced" and "exiting" 
> > could be used as "the pCPU is quiesced".
> > The concern with my approach is we would need to make sure that Xen 
> > correctly uses the rcu helpers. I know Juergen worked on that 
> > recently, but I don't know whether this is fully complete.
> I think it is complete, but I can't be sure, of course.
>
> One bit missing (for catching some wrong uses of the helpers) is this
> patch:
>
> https://lists.xen.org/archives/html/xen-devel/2020-03/msg01759.html
>
> I don't remember why it hasn't been taken, but I think there was a
> specific reason for that.
Looking at v8 and the patch is suitably reviewed by Jan. So I am a bit 
puzzled to why this wasn't committed... I had to go to v6 and notice the 
following message:
"albeit to be honest I'm not fully convinced we need to go this far."

Was the implication that his reviewed-by was conditional to someone else 
answering to the e-mail?
Cheers,

--
Julien Grall