[Xen-devel] Re: [PATCH] avoid injection of missed timer interrupts while debugging a guest

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 19 Apr 2006, at 22:28, Kamble, Nitin A wrote:

>   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?
Yes, you've got it. It is rather a pain as you note -- you essentially 
want a notifier on pause so the hvm code can maintain this flag that 
you can check-and-clear the next time you try to account missed ticks. 
On the other hand, a check for debugger mode is a bit gross and bizarre 
in the guts of HVM timer handling code. :-) I would at least like to 
see a patch that tries the more general approach and then we can pick 
between them.
There is also the question of whether or not we do generally want to 
account missed ticks if a domain is paused for some reason. But I'm 
pretty sure the answer is 'no'.
 -- Keir


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