Re: Null scheduler and vwfi native problem

[Julien Grall <julien@xxxxxxx>]

Hi Dario,

On 30/01/2021 17:59, Dario Faggioli wrote:
> On Fri, 2021-01-29 at 09:08 +0100, Anders Törnqvist wrote:
> > On 1/26/21 11:31 PM, Dario Faggioli wrote:
> > > Thanks again for letting us see these logs.
> > Thanks for the attention to this :-)
> >
> > Any ideas for how to solve it?
> So, you're up for testing patches, right?
>
> How about applying these two, and letting me know what happens? :-D
>
> They are on top of current staging. I can try to rebase on something
> else, if it's easier for you to test.
>
> Besides being attached, they're also available here:
>
> https://gitlab.com/xen-project/people/dfaggioli/xen/-/tree/rcu-quiet-fix
>
> I could not test them properly on ARM, as I don't have an ARM system
> handy, so everything is possible really... just let me know.
>
> It should at least build fine, AFAICT from here:
>
> https://gitlab.com/xen-project/people/dfaggioli/xen/-/pipelines/249101213
>
> Julien, back in:
>
>   
> https://lore.kernel.org/xen-devel/315740e1-3591-0e11-923a-718e06c36445@xxxxxxx/
>
>
> you said I should hook in enter_hypervisor_head(),
> leave_hypervisor_tail(). Those functions are gone now and looking at
> how the code changed, this is where I figured I should put the calls
> (see the second patch). But feel free to educate me otherwise.
enter_hypervisor_from_guest() and leave_hypervisor_to_guest() are the 
new functions.
I have had a quick look at your place. The RCU call in 
leave_hypervisor_to_guest() needs to be placed just after the last call 
to check_for_pcpu_work().
Otherwise, you may be preempted and keep the RCU quiet.

The placement in enter_hypervisor_from_guest() doesn't matter too much, 
although I would consider to call it as a late as possible.
Cheers,

--
Julien Grall