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Re: [PATCH 2/8] xen/evtchn: modify evtchn_alloc_unbound to allocate specified port
- To: Julien Grall <julien@xxxxxxx>
- From: Rahul Singh <Rahul.Singh@xxxxxxx>
- Date: Fri, 29 Jul 2022 12:35:37 +0000
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- Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- Delivery-date: Fri, 29 Jul 2022 12:36:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH 2/8] xen/evtchn: modify evtchn_alloc_unbound to allocate specified port
Hi Julien
> On 28 Jul 2022, at 9:50 pm, Julien Grall <julien@xxxxxxx> wrote:
>
> 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?
Yes, that will works for me. I will restrict the max event channel for domU
only and also add the comment in
"docs/misc/arm/device-tree/booting.txt” as suggested by you.
Regards,
Rahul
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