Re: [PATCH v2] tools/libxl: make default of max event channels dependant on vcpus

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Jürgen Groß writes ("Re: [PATCH v2] tools/libxl: make default of max event 
channels dependant on vcpus"):
> On 06.04.20 11:24, Julien Grall wrote:
> > Large guests on which arch? Which type of guests?
> 
> I'm pretty sure this applies to x86 only. I'm not aware of event
> channels being used on ARM for IPIs.

Should this be arch-dependent then ?  It seems like the figure is just
a heuristic anyway, and ...

> The resulting number would be larger than today only for guests with
> more than 96 vcpus. So I don't think the additional amount of memory
> is really that problematic.

Julien, are there likely to be any ARM guests now which have anywhere
near that number of vcpus ?  If not do we know now what such guests
are likely to be like ?

If this is all hypothetical on ARM it would seem silly to make this
arch-specific for the benefit of ARM given that the ARM implementation
would be entirely guesswork.  Maybe we should postpone that
specialisation until we know better what the ARM function should be
like for these large numbers of vcpus.

If ARM folks want to have a different formula for the default then
that is of course fine but I wonder whether this might do ARMk more
harm than good in this case.

Ian.