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Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration

To: "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 14 Mar 2011 15:03:48 +0000
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>>> On 14.03.11 at 15:39, Juergen Gross <juergen.gross@xxxxxxxxxxxxxx> wrote:
> On multi-thread multi-core systems an endless loop can occur in vcpu_migrate()
> with credit scheduler. Avoid this loop by changing the interface of pick_cpu
> to indicate a repeated call in this case.

But you're not changing in any way the loop that doesn't get
exited - did you perhaps read my original description as the
pick function itself looping (which - afaict - it doesn't)?

Further, the change still isn't consistent with idle_bias - the
updating ought to happen on the last iteration (if you need
to call the function more than once), not the first one, which
creates a chicken-and-egg problem for you as you will know
it's the last one only when it returned.

Jan


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