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RE: [Xen-devel] [Question] vcpu-set before or after xen_pause_requested

To: "Liu, Jinsong" <jinsong.liu@xxxxxxxxx>
Subject: RE: [Xen-devel] [Question] vcpu-set before or after xen_pause_requested
From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Date: Tue, 20 Apr 2010 19:47:12 +0100
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>, "alex.nixon@xxxxxxxxxx" <alex.nixon@xxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
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Liu, Jinsong writes ("RE: [Xen-devel] [Question] vcpu-set before or after 
xen_pause_requested"):
> How about this solution:
...
> In this way, old PV guest can still work in old way (no bad than
> before) with warning message, suggesting user to update their PV
> driver.

But, in new guests which are malfunctioning, things will not be
handled properly: the timeout will trigger and it will seem to have
worked.  (Consider a guest which is paused or is starved of CPU
because the host is very busy.)  There is also no good value for the
timeout.

I would suggest using a different xenstore key name for the new
protocol.  That way you don't get the feature with old drivers but at
least you don't make malfunctions worse with the new ones.

Ian.

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