From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: increase evtchn limits Date: Fri, 21 May 2010 10:25:57 +0100 Message-ID: References: <4BF64EDA020000780005E1FE@vpn.id2.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4BF64EDA020000780005E1FE@vpn.id2.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Jan Beulich , "mukesh.rathor@oracle.com" Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 21/05/2010 09:14, "Jan Beulich" 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