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[Xen-devel] Re: Large system boot problems

To: Bill Burns <bburns@xxxxxxxxxx>
Subject: [Xen-devel] Re: Large system boot problems
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 08 Feb 2008 15:45:45 +0000
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, "Carb, Brian A" <Brian.Carb@xxxxxxxxxx>
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On 8/2/08 15:22, "Bill Burns" <bburns@xxxxxxxxxx> wrote:

>> But ultimately the calibration code should be robust to long delays before
>> it is executed. It shouldn't go haywire. So something is bad there. Do you
>> have a dump of the decision made by the calibration code on cpu0 the very
>> first time it actually gets invoked? We probably need to trace the hell out
>> of that first invocation to work out why it gets things so badly wrong.
> I don't have more than in the earlier email where is shows the
> large delta in tsc time, which seems to cause the bogus result.

Okay, well looking at the inputs on that first invocation -- master_stime
and local_stime -- they are totally out of sync. One says that 9.3s has
elapsed since init_xen_time() was invoked, the other says that 4.6s has
elapsed (curiously exactly half the time). The former is correct if the CPU
really is a 3.4GHz part and is running at full speed for the duration. But
you ought to be able to work out which is the correct ballpark by timing
with a stopwatch the time between init_xen_time() and that first invocation
on cpu0 of local_time_calibration() (you'll have to printk() when
init_xen_time() is executed).

 -- Keir

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