[Qemu-devel] Re: [PATCH] fix halt emulation with icount and CONFIG_IOTHREAD (v2)

[Paolo Bonzini <pbonzini@redhat.com>]

On 02/16/2011 11:04 AM, Jan Kiszka wrote:
> On 2011-02-16 10:57, Paolo Bonzini wrote:
>> On 02/16/2011 10:46 AM, Jan Kiszka wrote:
>>> What should this be good for? The iothread already kicks the vcpu if it
>>> wants to acquire the contended global mutex.
>>
>> Assuming the VCPU is in the timedwait that Marcelo changed, the global
>> mutex is free and the iothread will not kick the VCPU.
>
> Then why should it kick it at all?

To make it notice something changed in all_cpu_threads_idle---but that's 
wrong, it should have been kicked in cpu_interrupt.

> If we change the halt condition, we should not kick the vcpus but only
> signal the condition variable. Actually, I've a patch queued that skips
> pointless qemu_thread_signal in qemu_cpu_kick for TCG.

Yes, I was kicking just because that's the wrapper that is used to 
signal the condition variable---just like I was kicking in my patches to 
eliminate timedwait.

>> So, perhaps the correct fix is to kick the cpu in cpu_interrupt, and all
>> I wrote about timeouts and timers is wrong.  My patch would band-aid it.
>
> That's my strong suspect. We really need to understand what goes wrong.

I agree on both counts.

Paolo