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Re: [Xen-devel] increase evtchn limits

To: <keir.fraser@xxxxxxxxxxxxx>,<mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] increase evtchn limits
From: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Date: Fri, 21 May 2010 09:14:01 +0100
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>>> 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.


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