Re: [Qemu-devel] [RFC PATCH V6 06/18] tcg: remove tcg_halt_cond global variable.

[Frederic Konrad <fred.konrad@greensocs.com>]

On 07/07/2015 14:27, Alex Bennée wrote:
> Frederic Konrad <fred.konrad@greensocs.com> writes:
>
>> On 26/06/2015 17:02, Paolo Bonzini wrote:
>>> On 26/06/2015 16:47, fred.konrad@greensocs.com wrote:
>>>> From: KONRAD Frederic <fred.konrad@greensocs.com>
>>>>
>>>> This removes tcg_halt_cond global variable.
>>>> We need one QemuCond per virtual cpu for multithread TCG.
>>>>
>>>> Signed-off-by: KONRAD Frederic <fred.konrad@greensocs.com>
> <snip>
>>>> @@ -1068,7 +1065,7 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
>>>>                    qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
>>>>                }
>>>>            }
>>>> -        qemu_tcg_wait_io_event();
>>>> +        qemu_tcg_wait_io_event(QTAILQ_FIRST(&cpus));
>>> Does this work (for non-multithreaded TCG) if tcg_thread_fn is waiting
>>> on the "wrong" condition variable?  For example if all CPUs are idle and
>>> the second CPU wakes up, qemu_tcg_wait_io_event won't be kicked out of
>>> the wait.
>>>
>>> I think you need to have a CPUThread struct like this:
>>>
>>>      struct CPUThread {
>>>          QemuThread thread;
>>>          QemuCond halt_cond;
>>>      };
>>>
>>> and in CPUState have a CPUThread * field instead of the thread and
>>> halt_cond fields.
>>>
>>> Then single-threaded TCG can point all CPUStates to the same instance of
>>> the struct, while multi-threaded TCG can point each CPUState to a
>>> different struct.
>>>
>>> Paolo
>> Hmm probably not, though we didn't pay attention to keep the non MTTCG
>> working.
>> (which is probably not good).
> <snip>
>
> You may want to consider push a branch up to a github mirror and
> enabling travis-ci on the repo. That way you'll at least know how broken
> the rest of the tree is.
>
> I appreciate we are still at the RFC stage here but it will probably pay
> off in the long run to try and avoid breaking the rest of the tree ;-)
>
Good point :)

Fred