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[Xen-devel] RE: latest xen-unstable fails to boot on Dell D630 (likely h

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] RE: latest xen-unstable fails to boot on Dell D630 (likely hpet/Cstate problem)
From: "Yu, Ke" <ke.yu@xxxxxxxxx>
Date: Tue, 8 Dec 2009 15:07:31 +0800
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Thread-topic: latest xen-unstable fails to boot on Dell D630 (likely hpet/Cstate problem)
>-----Original Message-----
>In this thread, I observed that I was unable to
>provoke deep C state (C3) on my Dell D630, which has
>a Intel Merom (dual-core laptop) processor.  At that
>time, when I tried enabling hpetbroadcast, dom0 boot failed.
>As it turned out, all RHEL5-based (maybe RHEL4- also) dom0
>default installation run /sbin/hwclock, which IIRC takes
>the RTC away from Xen and gives it to dom0.  Since the
>Xen hpet emulation does not do RTC emulation, bad things
>then happen when a deep Cstate is entered (dom0 apparently
>never wakes up).  I think Ke Yu has also reproduced this problem.
>Sometime in the last few weeks, some patch in xen-unstable
>apparently changed some defaults and xen-unstable will
>no longer boot with this processor/dom0, with or without
>hpetbroadcast on the Xen command line.  However, specifying
>max_cstate=2 on the Xen command line allows a successful
>dom0 boot, so I suspect the problem is the same (or at
>least very similar).
>I did a quick scan for hpet changes and found c/s 20497,
>but backing it out made no difference.
>I have a workaround for now, but since it is likely that
>many customers (including all of Oracle's OVS customers)
>use a RHEL5-based dom0 boot sequence, and Merom processors
>work fine otherwise, it would be nice to get this identified
>and fixed before 4.0.

Let's firstly figure out which component the issue resides. 

Firstly, in the default boot (i.e. without specifying max_cstate=2), when dom0 
hangs, is xen still alive, E.g. can Xen response to three Ctrl-'A' in serial?

If only dom0 hangs, it is probably that RTC malfunction make incorrect dom0 
time and lead dom0 fail to boot. Then RTC emulation in hypervisor should fix 
this issue.

If Xen also hangs, it should be another bug, i.e. hpet broadcast does not wake 
up CPU in deep C states. in this case, if convenient, could you help to do some 
bisect to see which cset cause this bug?

Best Regards
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