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Re: [Xen-devel] Implement 3-level event channel routines in Linux.

On Wed, Jan 02, 2013 at 06:46:58PM +0000, Wei Liu wrote:
> On Wed, 2013-01-02 at 18:26 +0000, Konrad Rzeszutek Wilk wrote:
> > On Mon, Dec 31, 2012 at 06:38:54PM +0000, Wei Liu wrote:
> > > This patch series implements 3-level event channel routines in Linux 
> > > kernel.
> > > 
> > > My thought is that 3-level event channel is only useful for Dom0 or driver
> > > domain, so it is not enabled by default. Enable it with evtchn_level=3 in
> > > kernel command line.
> > 
> > Could it be enabled dynamically? Say when we are close to exhausting the
> > amount of channels? Or if the machine has some large amount of memory and
> > hence would probably allocate many many guests?
> > 
> Do you mean enabling this mechanism on the fly when Dom0 / driver domain
> is running? Or do you mean enabling it based on some metrics when
> starting up a domain?

Either one.
> If it is the first case, who is responsible for initiating the switching
> process? It looks like it is Xen's responsibility to do the switch
> because Dom0 sometimes cannot know the true capability of underlying
> hardware. If it is Xen, then we need to add callback to poke Dom0 /
> driver domain.

Huh? It would be as simple as Dom0 just figuring out that it is
at the end of the available events (b/c its close to the MAX) and
then transitioning to the 3-level one (if it can).

> For both cases, what do you have in mind for the metric that used to
> trigger the switch? How much RAM / how many CPUs is the threshold?

No idea. At what point are we running out of the events?
> Wei.
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