From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [PATCH] Dont' round-robin the callback interrupt Date: Tue, 13 Jul 2010 06:59:34 +0200 Message-ID: <4C3BF2B6.4050807@ts.fujitsu.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: Tim Deegan , Paul Durrant , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 07/12/2010 07:41 PM, Keir Fraser wrote: > On 12/07/2010 18:17, "Keir Fraser" wrote: > >>> However, that's not the motivation for this patch. In the windows code, we >>> only bind event channels to vcpu 0 since we cannot get callback interrupts on >>> multiple vcpus simultaneously, since the interrupt is level sensitive. Thus >>> round-robining is wasteful in terms of kicking certain data structures >>> between >>> caches (assuming a reasonably constant vcpu -> pcpu mapping). >> >> Surely that argument can be made for any interrupt that is set up to >> round-robin among multiple CPUs? Obviously in the PV drivers case the >> event-channel IRQ is probably the only significant source of round-robin >> interrupts. But I don't see that it's special in any other way. > > Further, the correct semantics for LowestPrio delivery was implemented by > Juergen Gross at Fujitsu for a reason. Cc'ing him. I suspect he will say > that relaxing the delivery semantics will cause something he cares about to > break. Thanks for CC'ing me, Keir. Selecting different CPUs gives at least our BS2000 system a performance win of a few percent. As Keir already said, that's the reason I implemented the LPP delivery of interrupts. If you really need a different interrupt delivery behaviour I would at least recommend a per-domain parameter for violating the correct semantics using the LPP delivery as default. Juergen -- Juergen Gross Principal Developer Operating Systems TSP ES&S SWE OS6 Telephone: +49 (0) 89 3222 2967 Fujitsu Technology Solutions e-mail: juergen.gross@ts.fujitsu.com Domagkstr. 28 Internet: ts.fujitsu.com D-80807 Muenchen Company details: ts.fujitsu.com/imprint.html