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Re: [Qemu-devel] KVM brokenness due to IO thread changes

From: Anthony Liguori
Subject: Re: [Qemu-devel] KVM brokenness due to IO thread changes
Date: Tue, 28 Apr 2009 15:09:57 -0500
User-agent: Thunderbird (X11/20090320)

Jan Kiszka wrote:
Marcelo Tosatti wrote:

On Tue, Apr 28, 2009 at 09:40:01AM +0200, Jan Kiszka wrote:

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.


Anthony Liguori

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