From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.fraser@eu.citrix.com>
Subject: Re: Patch: implementing least priority interrupt routing
Date: Tue, 18 Nov 2008 10:10:47 +0000
Message-ID: <C5484527.1F525%keir.fraser@eu.citrix.com>
References: <49229202.3030505@fujitsu-siemens.com>
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To: Juergen Gross <juergen.gross@fujitsu-siemens.com>, xen-devel@lists.xensource.com
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On 18/11/08 09:59, "Juergen Gross" <juergen.gross@fujitsu-siemens.com>
wrote:

> the attached patch implements interrupt routing to least priority processor
> for HVM domains.
> Instead of round robin the vcpu with the lowest processor priority is selected
> for the interrupt. If multiple vcpus share the same low priority interrupts
> are distributed between those round robin.
> Tested with BS2000 domain (3 vcpus, idle processors are now preferred
> interrupt target).

Where idle means 'not processing an interrupt'. Which ought to be by far the
most common case even for a non-idle CPU. Does this really improve load
balancing all that much? Does BS2000 spend lots of time in IRQ context?

My fear is that extra complexity here slows down dest_lowprio for all OSes
(and it's used by a lot of OSes) for every ExtInt delivered.

 -- Keir