Re: RT-Xen on ARM

From: Dario Faggioli <dario.faggioli@citrix.com>
To: Meng Xu <xumengpanda@gmail.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
	Andrii Anisov <andrii_anisov@epam.com>
Subject: Re: RT-Xen on ARM
Date: Wed, 12 Jul 2017 08:13:01 +0200	[thread overview]
Message-ID: <1499839981.7756.11.camel@citrix.com> (raw)
In-Reply-To: <CAENZ-+mhn6=Ta9xfUsumNW_wTsR5KJ9p78CQkRDWS=uQ8ivbxQ@mail.gmail.com>

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On Fri, 2017-07-07 at 14:29 -0400, Meng Xu wrote:
> On Wed, Jul 5, 2017 at 4:29 AM, Dario Faggioli
> <dario.faggioli@citrix.com> wrote:
> > 
> The total utilization can help answer if the VCPU parameters are
> feasible or not.
>
I'm just saying that we could keep track of utilization and, if on an
host with N CPUs, we reach more than (N*100)%, we can warn the user
that deadlines will be missed.

This is a simple enough check, and it can live in the hypervisor.

> But I'm thinking there may exist a better (yet optimal) approach to
> answer the question: If all VCPUs on K cores are globally scheduled
> or
> completely partitioned onto each of the K cores, we can use
> Utilization Bound of the EDF scheduling algorithm for checking if the
> VCPU's performance can be safely provided.
> This requires the VCPUs' parameters (which also computes the total
> utilization), which are easy to get.
> 
I know there's math we can use, I'm just saying we don't want that in
Xen.

> Another thing is where this schedulability check should be provided:
> in Xen kernel, in Xen toolstack, or as a separate utility tool?
> In my opinion, a separate utility tool seems to be better than the
> other tool approaches?
> 
Exactly. As said above, you don't put something as complex as that
inside Xen. It can well live in toolstack, IMO, as far as we also add a
(global, non per-domain) for telling whether we want admission or
control not.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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