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[Xen-devel] latest xen-unstable fails to boot on Dell D630 (likely hpet/

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Subject: [Xen-devel] latest xen-unstable fails to boot on Dell D630 (likely hpet/Cstate problem)
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 7 Dec 2009 15:31:10 -0800 (PST)
Cc: "Yu, Ke" <ke.yu@xxxxxxxxx>
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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.


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