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

From: Marcelo Tosatti
Subject: Re: [Qemu-devel] KVM brokenness due to IO thread changes
Date: Tue, 28 Apr 2009 09:51:46 -0300
User-agent: Mutt/1.5.18 (2008-05-17)


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.

> Moreover:
>   CC    i386-softmmu/vl.o
> /data/qemu/vl.c:4380: warning: ‘qemu_calculate_timeout’ defined but not used
> Jan

BTW, can you please review the changes made to the debugging logic in
the main loop sometime? (there's a debug_requested global now).

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