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Date: Mon, 17 Dec 2007 23:36:27 +0200
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Subject: Re: [Qemu-devel] qemu vl.c
References: <E1J3tMn-0001vY-5p@cvs.savannah.gnu.org>	<200712161430.35113.paul@codesourcery.com>	<476543A0.9090207@flac.kalibalik.dk>
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To: qemu-devel@nongnu.org
Cc: Anders <mail@flac.kalibalik.dk>

Paul Brook wrote:
> On Sunday 16 December 2007, Anders wrote:
>   
>> Paul Brook wrote:
>>     
>>>> 	Redundant timer rearm optimisation by Anders Melchiorsen.
>>>>         
>>> I think this is incorrect.
>>>
>>> When a timer is modified, we need to rearm the host timer immediately. We
>>> can not wait for the old timer to fire, or for execution to fall back to
>>> the main_loop_wait.  Consider the case where the guest adds a timer
>>> interrupt and immediately enters a tight loop - Quite a common operation
>>> when calibrating a software delay loop. The timer won't be rearmed until
>>> some other event occurs. It the system is otherwise quiescent and you're
>>> not using SDL output it may never occur.
>>>       
>> Hi Paul,
>>
>> I am certainly open to it not being correct, but currently I fail to see
>> how it changes the scenario that you mention. The rearming is moved away
>> from qemu_run_timers(), not qemu_mod_timer(). Can you elaborate?
>>     
>
> It's possible that this code has always been broken. You changes make it much 
> more obviously so.
>
>   

I'm merging qemu-cvs into the kvm repository now, and with this commit 
in, kvm will hang after about a minute.  Attaching to it with gdb or 
strace will cause it to resume, so this is very likely a missing signal 
problem.

(qemu will happily run with this patch; kvm is much more sensitive to 
missed signals).


-- 
Any sufficiently difficult bug is indistinguishable from a feature.