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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Feb 02, 2017 at 04:22:53AM -0700, Jan Beulich wrote:
> >>> On 01.02.17 at 19:21, <wei.liu2@xxxxxxxxxx> wrote:
> > On Tue, Jan 31, 2017 at 04:30:50PM +0000, Julien Grall wrote:
> >> 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?
> > 
> > Worth checking all the RCU docs in Linux (Documentation/RCU).
> > 
> > I think there are descriptions about idle or no-tick variants. It would
> > be useful to know how Linux handles this. I suspect RCU in Linux is more
> > capable than the one in Xen...
> 
> Isn't all we need an rcu_idle_{enter,exit}() implementation (and of
> course calls to them placed where needed)?
> 

I'm no RCU expert, but having checked Linux source code and the
documentation of rcu_idle_{enter,exit}, what you said makes sense to me.

Wei.

> Jan
> 

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