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Message-ID: <49F76295.2010403@codemonkey.ws>
Date: Tue, 28 Apr 2009 15:09:57 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] KVM brokenness due to IO thread changes
References: <49F6B2D1.8070906@web.de> <20090428125146.GB19142@amt.cnet>
	<49F75F67.9040402@web.de>
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To: Jan Kiszka <jan.kiszka@web.de>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

Jan Kiszka wrote:
> Marcelo Tosatti wrote:
>   
>> Jan,
>>
>> On Tue, Apr 28, 2009 at 09:40:01AM +0200, Jan Kiszka wrote:
>>     
>>> Hi,
>>>
>>> this is a heads-up, maybe someone has some time to look into this over
>>> the day: I seems like the IO thread changes caused a few regressions to
>>> the KVM mode.
>>>
>>> When I keep this feature disabled, I see strange hick-ups of the event
>>> delivery mechanism, and the guest stops once in a while for a second or
>>> so. Attaching strace makes the whole process terminate early (looks like
>>> it triggers a race in the signal handling). And when I enable the IO
>>> thread, I immediately get a deadlock on qemu_global_mutex.
>>>       
>> Yes its borked. The iothread should signal the vcpu thread whenever it
>> wants to grab the mutex lock, because unlike kvm-userspace it does not
>> drop the global mutex when entering guest mode (VCPU_RUN ioctl).
>>
>> Anthony will commit patches to fix that soon.
>>     
>
> Looking forward. It's far more efficient to test my infrastructure
> changes against the KVM mode.
>   

N.B. he's seeing issues with the IO thread disabled.

I've not seen this myself and my patch doesn't fix that problem.

Regards,

Anthony Liguori