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Re: [Xen-devel] [PATCH v1] libxl: remove limit for default number of event channels


On 27/03/2020 14:37, Olaf Hering wrote:
On Fri, Mar 27, Ian Jackson wrote:

This seems likely to be right, but: what is the default in Xen ?  Is
it sufficiently tight to stop a guest using too many resources ?

The value of d->max_evtchns will be either 4k or 128k.
AFAICS no extra resources are allocated with the changed value.

Event channels are allocated using buckets. Everytime you will a bucket, a new bucket will be allocated.

By increasing the limit, you effectively increase the number of buckets than can be allocated.

So while I agree that the default allocation will be the same, you effectively allow the guest to use more resource in Xen. Therefore I don't think this is acceptable to lift the limits for all the guests.


Julien Grall



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