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Re: [Xen-devel] [PATCH] Dont' round-robin the callback interrupt

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>

From: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>

Date: Tue, 13 Jul 2010 06:59:34 +0200

Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>

Delivery-date: Mon, 12 Jul 2010 22:00:47 -0700

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On 07/12/2010 07:41 PM, Keir Fraser wrote:

On 12/07/2010 18:17, "Keir Fraser"<keir.fraser@xxxxxxxxxxxxx>  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@xxxxxxxxxxxxxx Domagkstr. 28 Internet: ts.fujitsu.com D-80807 Muenchen Company details: ts.fujitsu.com/imprint.html _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel

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