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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/03/2020 09:45, 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.
>
> Instead of requiring to specify the allowed number of event channels
> via the "event_channels" domain config option, make the default
> depend on the maximum number of vcpus of the guest.
>
> In order not to regress current configs use 1023 as the minimum
> default setting.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

:(

I suspect I regressed this by making it not actually dead code.

1023 is the 32bit EVT 2L ABI limit, but until I moved max_evtchn into
the createdomain hypercall, I'm pretty sure a limit never used to get set.

If this is the case, then unlimited should be the default.

~Andrew