Re: [PATCH 2/8] xen/evtchn: modify evtchn_alloc_unbound to allocate specified port

[Julien Grall <julien@xxxxxxx>]

Hi Rahul,

On 28/07/2022 16:37, Rahul Singh wrote:
> As you mentioned, if we don’t restrict the number of events channel for the 
> dom0 system will boot slower.
> This is a good reason to restrict the number of event channels for dom0.
Let me start that I am still fine if you want to push for a new 
parameter (so long it is not Arm specific). However, I am afraid that I 
will not be able to argue for it because I don't see a strict need for it.
Let me play the devil's advocate for a bit. AFAIU, you would like to 
introduce the new parameter just to tell the admin the boot is going to 
be slower if you use a event channel ID higher than N.
To me this sounds like the same as if an admin decide to use 10GB rather 
than 1GB. There will be slow down.
This slowness is only boot specific and will not vary. So one could 
argue this is easily noticeable and an admin can take remediation.
Given Jan's objection, I would like to propose to document it in the 
bindings instead (a concerned admin will likely read it). Below a rough 
proposal for the documentation:
"It is recommended to use low event channel ID."

Would that be suitable for you?

Cheers,

--
Julien Grall