Re: [Xen-devel] [RFC PATCH 2/5] XL: Increase event channels to support more vcpus

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.08.17 at 11:11, <tianyu.lan@xxxxxxxxx> wrote:
> On 8/25/2017 6:04 PM, Wei Liu wrote:
>> On Fri, Aug 25, 2017 at 10:57:26AM +0100, Roger Pau Monné wrote:
>>> On Fri, Aug 25, 2017 at 10:18:24AM +0100, Wei Liu wrote:
>>>> On Thu, Aug 24, 2017 at 10:52:17PM -0400, Lan Tianyu wrote:
>>>>> This patch is to increase event channels to support more vcpus in single 
>>>>> VM.
>>>>>
>>>>> Signed-off-by: Lan Tianyu <tianyu.lan@xxxxxxxxx>
>>>>
>>>> There is no need to bump the default. There is already a configuration
>>>> option called max_event_channel.
>>>
>>> Maybe make this somehow based on the number of vCPUs assigned to the
>>> domain?
>>>
>>> It's not very used-friendly to allow the creation of a domain with 256
>>> vCPUs for example that would then get stuck during boot.
>>>
>>> Or at least check max_event_channel and the number of vCPUs and print
>>> a warning message to alert the user that things might go wrong with
>>> this configuration.
>>>
>> 
>> The problem is number of vcpu is only one factor that would affect the
>> number of event channels needed.
> 
> How about producing a warning about event channel maybe not enough when 
> vcpu number is >128 and still uses default max event channel number?

There would be nothing wrong with that for a guest not using
PV drivers, or not requiring multiple channels per vCPU. Hence
I'm not convinced a warning is appropriate here.

Jan

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