Re: [Xen-devel] [PATCHv4 0/11] Xen: FIFO-based event channel ABI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.09.13 at 20:41, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> On Fri, Sep 27, 2013 at 11:55:48AM +0100, David Vrabel wrote:
>> This is a complete implementation of the hypervisor and xl toolstack
>> parts of the FIFO-based event channel ABI described in this design
>> document:
>> 
>> http://xenbits.xen.org/people/dvrabel/event-channels-F.pdf 
>> 
>> Changes in draft F are:
>> 
>> - READY field in the control block is now 32-bits (so guests only need
>>   to support atomic bit ops on 32-bit words).  This is only a
>>   documentation change as the implementation already used a uint32_t.
>> 
>> - DOMCTL_set_max_evtchn replaces EVTCHNOP_set_limit.
>> 
>> - DomUs default to unlimited number of event channels requiring
>>   the toolstack to set a limit.
>> 
>> The toolstack defaults to limiting guests to 127 event channels if the
>> event_channels option is omitted.  This means the minimum amount of
>> both Xen heap and global mapping space is used regardless of which ABI
>> is used.  If this is considered too restrictive a limit, 1023 would be
>> another sensible default (limits the guest to a single event array
>> page but 5 xenheap pages for the struct evtchns).
> 
> I would say 1023 (so the same value as the existing event mechanism)
> would be a sensible default.

That's the existing 32-bit default; 64-bit has 4095 (yet that surely
would be needlessly high as the new default).

Jan


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