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Re: [Xen-devel] softtsc for PV guests

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] softtsc for PV guests
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Fri, 21 Aug 2009 16:02:18 -0700
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On 08/21/09 15:17, Dan Magenheimer wrote:
> I'm starting to play with implementing softtsc for
> PV guests, but am not adequately familiar with the low
> level x86 instruction set or emulation code in Xen.
> The attached patch seems to work fine for awhile.
> Dom0 begins the boot process and the printk added
> to traps.c observes more than 256K TSC traps (mostly
> in the BogoMIPS calculation) and continues on loading
> drivers etc but eventually freezes after:

The Xen clocksource uses rdtsc extensively for timing; emulating it
would be a bad idea.  I guess it would make some sense to emulate
usermode rdtsc, but it shouldn't affect kernel rdtscs.

> device-mapper: ioctl: 4.7.0-ioctl (2006-06-24) initialised: 
> dm-devel@xxxxxxxxxx
> kjournald starting.  Commit interval 5 seconds
> EXT3-fs: mounted filesystem with ordered data mode.
> Any ideas on what might be stopping the dom0 boot?

How dead is the system?  Does it respond to sysrq-p?  'q' or '0' on the
Xen console?


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