Re: [Xen-devel] xen/arm: Domain not fully destroyed when using credit2

[Julien Grall <julien.grall@xxxxxxx>]

Hi Dario,

On 25/01/17 16:00, Dario Faggioli wrote:
> On Wed, 2017-01-25 at 12:38 +0000, Julien Grall wrote:
> > On 25/01/17 11:10, Dario Faggioli wrote:
> And a good one. I may be wrong (I certainly wasn't around at the time),
> but ISTR out RCU code is imported/inspired by Linux... Looking there
> again may help, but, nowadays, Linux RCU subsystem is a Lernaean Hydra
> monster, with 100 heads and sharpen claws! :-O
>
> And, while, in there, it has to be like that, I don't think we need all
> such complexity, and hence we can't just re-sync. :-/
Yeah, even the tiny RCU code is quite complex :/. I've looked at our RCU 
code and noticed there is a link in the header to [1].
It seems to be a documentation about the RCU code we used. From my 
understanding of the "RCU Implementations", the authors are expecting a 
timer to kick periodically pCPU and check if there is some RCU work pending.
We could add this timer but it would prevent an idle pCPU to stay in low 
power mode for a long time. Another solution would be to send an 
interrupt to each pCPU when call_rcu is called rather depending on a 
mark. Although this would still wake-up the pCPU even it was doing nothing.
Any better ideas?

Cheers,

[1] http://lse.sourceforge.net/locking/rcupdate.html

--
Julien Grall

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