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Re: [Xen-devel] [timer/ticks related] dom0 hang during boot on large 1TB

To: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] [timer/ticks related] dom0 hang during boot on large 1TB system
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 21 Dec 2009 11:55:09 -0800
Cc: "kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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On 12/21/2009 11:52 AM, Mukesh Rathor wrote:
On Mon, 21 Dec 2009 19:07:39 +0000
Keir Fraser<keir.fraser@xxxxxxxxxxxxx>  wrote:

On 21/12/2009 18:20, "Dan Magenheimer"<dan.magenheimer@xxxxxxxxxx>

Not to say the problem can't or shouldn't be fixed in Xen.
Keir, would bad things happen if construct_dom0 is done after
scrub_heap_pages()?  Other than some time wastage because
dom0's memory would get scrubbed just before it gets
overwritten (which is admittedly a much bigger problem
when dom0_mem is not specified in the Xen boot line
on a machine with ginormous memory).
The problem is more likely that Xen system time started ticking some
time earlier during boot process. I doubt it is to do with ordering of
construct_dom0 versus boot-time scrubbing.

  -- Keir

The problem is exactly how Dan described it. 'delta' for first interrupt
in dom0->timer_interrupt() goes up proportionately with amount of memory
on system. On this box, it appears more than 600GB causes delta to be
large enough to wrap jiffies.

  1TB delta: 940b7d68a4
32GB delta: 02ae56eadb

xen->send_guest_vcpu_virq() ---->  dom0->handle_IRQ() ->  timer_interrupt()

timer_interrupt will call do_timer delta/NS_PER_TICK number of times.

How is it computing that delta?

Anyway, I'm not at all sure this will apply to a pvops dom0 kernel as it does timekeeping quite differently from 2.6.18-xen.


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