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

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Avoid endless loop for vcpu migration
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Mon, 14 Mar 2011 15:06:36 +0000
Cc: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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At 15:03 +0000 on 14 Mar (1300115028), Jan Beulich wrote:
> >>> 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.

Perhaps you could submit a comment patch that describes exactly what
idle_bias is and how it's supposed to work.  At the moment it's entirely


Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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