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

On 26.03.2020 11:00, Jürgen Groß wrote:
> On 26.03.20 10:54, Jan Beulich wrote:
>> On 26.03.2020 10:45, Juergen Gross wrote:
>>> Today the maximum number of event channels for a guest is defaulting
>>> to 1023. For large guests with lots of vcpus this is not enough, as
>>> e.g. the Linux kernel uses 7 event channels per vcpu, limiting the
>>> guest to about 140 vcpus.
>> I don't think any particular guest OS should "dictate" the default
>> here. What if another OS (or even a future version of Linux) requires
>> more than 8? And why would the value depend on number of vCPU-s but
>> not number and kind of virtual devices?
> It is a rough estimate. And with HVM guests being limited to 128 cpus
> anyway, this problem is more relevant for PV guests, limiting the
> available options for guest OS's.

How many evtchns would e.g. mini-os require? I.e. wouldn't such stubdoms
get a much larger than necessary allowance this way?




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