Re: sched=null vwfi=native and call_rcu()

[Julien Grall <julien@xxxxxxx>]

On 06/01/2022 00:40, Stefano Stabellini wrote:
> Hi all,
Hi,

> As you might remember, we have an outstanding issue with call_rcu() when
> sched=null vwfi=native are used. That is because in that configuration
> the CPU never goes idle so rcu_idle_enter() never gets called.
>
> The issue was caught on the field and I managed to repro the problem
> doing the following:
>
> xl destroy test
> xl create ./test.cfg
>
> Resulting in the following error:
>
> # Parsing config from ./test.cfg
> # (XEN) IRQ 54 is already used by domain 1
>
> The test domain has 3 interrupts remapped to it and they don't get
> released before the new domain creation is requested.
>
> Just FYI, the below hacky patch seems to reliably work-around the
> problem in my environment.
>
> Do you have any suggestions on what would be the right way to solve
> this issue?
This issue and solution were discussed numerous time on the ML. In 
short, we want to tell the RCU that CPU running in guest context are 
always quiesced. For more details, you can read the previous thread 
(which also contains a link to the one before):
https://lore.kernel.org/xen-devel/fe3dd9f0-b035-01fe-3e01-ddf065f182ab@xxxxxxxxx/

Cheers,

--
Julien Grall