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Re: [Xen-devel] increase evtchn limits

To: Jan Beulich <jbeulich@xxxxxxxxxx>, "mukesh.rathor@xxxxxxxxxx" <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] increase evtchn limits
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 21 May 2010 10:25:57 +0100
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On 21/05/2010 09:14, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

>>>> Keir Fraser  05/21/10 9:06 AM >>>
>> How many CPUs do you have to bring up? How many event channels are we
>> squandering per CPU in PV Linux right now (can you enumerate them)?
> There are 5 event channels per CPU (timer, reschedule IPI, SMP call function
> IPI, SMP call function single IPI, and spinlock wakeup IPI).
> While 4096 may seem plenty, I don't think it really is: With larger systems
> you not only have more CPUs, but you also generally have more devices (with
> e.g. MSI-X ones possibly requiring quite a number of event channels per
> device) plus you also expect to be able to run more guests, which in turn
> requires more event channels in Dom0. So I agree with Mukesh that we ought to
> find a reasonable way to overcome this limit.

Has the event channel limit *actually* been hit? Or is this another "what if
we had over a thousand CPUs" scenario?

 -- Keir

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