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Re: Null scheduler and vwfi native problem

Hi Juergen,

On 03/02/2021 11:00, Jürgen Groß wrote:
On 03.02.21 10:19, Julien Grall wrote:

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
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


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?


Julien Grall



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