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[Xen-devel] RE: [PATCH] avoid injection of missed timer interrupts while

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: [Xen-devel] RE: [PATCH] avoid injection of missed timer interrupts while debugging a guest
From: "Kamble, Nitin A" <nitin.a.kamble@xxxxxxxxx>
Date: Wed, 19 Apr 2006 14:28:00 -0700
Cc: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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Thread-index: AcZj7uyotHwTLEx6SLypyeBTAdhljwABzrkw
Thread-topic: [PATCH] avoid injection of missed timer interrupts while debugging a guest
Hi Keir,
  Gdbserver does use the xc_ptrace(PTRACE_ATTACH), and the PTRACE_ATTACH uses 
xc_domain_pause() to pause the running guest for debugging.
  This is the same interface called by "xm pause". 
One more thing, the PIT missed timer ticks injection code is invoked later 
after the domain is un-paused, so at the time of that invocation the domain is 
no more paused.
  I think what you are saying can be achieved by keeping a flag that will tell 
the PIT code that the domain was paused & unpaused and so if you have missed 
ticks do not try to inject it.
  Did I understand you correctly, and do you think the "domain_was_paused" flag 
is the right solution?

Thanks & Regards,
Open Source Technology Center, Intel Corp

>-----Original Message-----
>From: Keir Fraser [mailto:Keir.Fraser@xxxxxxxxxxxx]
>Sent: Wednesday, April 19, 2006 1:18 PM
>To: Kamble, Nitin A
>Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Ian Pratt
>Subject: Re: [PATCH] avoid injection of missed timer interrupts while
>debugging a guest
>On 19 Apr 2006, at 21:02, Kamble, Nitin A wrote:
>> Hi Keir, Ian,
>> Today if we stop the guest for debugging using the gdbserver and then
>> continue with the guest execution the PIT finds that the time has gone
>> ahead and it missed to inject so many timer ticks, and it tries to
>> inject all of those one by one. So after the gdb continue command the
>> guest just handles the timer interrupts for a long time before it can
>> do anything else.
>>     This patch changes this PIT behavior, if it finds that the guest
>> is being debugged then it does not try to inject missing timer ticks.
>How about not accounting missed ticks across DOMF_ctrl_pause'd periods?
>This would mean that missing_ticks would still be accounted for a
>DOMF_debugger guest that is not currently being debugged, and will also
>nicely handle any other circumstances in which a guest might get paused
>by control software for any reason. I suppose it'll be a bigger patch
>  -- Keir

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