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

[Jan Kiszka <jan.kiszka@siemens.com>]

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?

> 
>> And when the vcpu thread is
>> in halt state, kicking it should change no other state.
> 
> Kicking the VCPU will start running it, if an interrupt request from the 
> devices caused cpu_has_work to become true (and hence 
> all_cpu_threads_idle to become false).

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.

> 
> 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.

Jan

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