Re: [PULL 3/5] softmmu/cpus: Only set parallel_cpus for SMP

[Philippe Mathieu-Daudé]

On 9/7/20 6:30 PM, Claudio Fontana wrote:
> On 9/7/20 12:20 PM, Philippe Mathieu-Daudé wrote:
>> On 9/7/20 12:05 PM, Claudio Fontana wrote:
>>> Hi Richard,
>>>
>>> currently rebasing on top of this one,
>>> just a question, why is the patch not directly using "current_machine"?
>>
>> For user mode?
> 
> In user mode I'd not expect softmmu/cpus.c to be built at all...

Which is why :) current_machine is NULL in user-mode.

> 
> Ciao,
> 
> Claudio
> 
>>
>>>
>>> Is using MACHINE(qdev_get_machine()) preferrable here?
>>>
>>> Thanks,
>>>
>>> Claudio
>>>
>>> On 9/3/20 11:40 PM, Richard Henderson wrote:
>>>> Do not set parallel_cpus if there is only one cpu instantiated.
>>>> This will allow tcg to use serial code to implement atomics.
>>>>
>>>> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>>>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>>>> ---
>>>>  softmmu/cpus.c | 11 ++++++++++-
>>>>  1 file changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/softmmu/cpus.c b/softmmu/cpus.c
>>>> index a802e899ab..e3b98065c9 100644
>>>> --- a/softmmu/cpus.c
>>>> +++ b/softmmu/cpus.c
>>>> @@ -1895,6 +1895,16 @@ static void qemu_tcg_init_vcpu(CPUState *cpu)
>>>>      if (!tcg_region_inited) {
>>>>          tcg_region_inited = 1;
>>>>          tcg_region_init();
>>>> +        /*
>>>> +         * If MTTCG, and we will create multiple cpus,
>>>> +         * then we will have cpus running in parallel.
>>>> +         */
>>>> +        if (qemu_tcg_mttcg_enabled()) {
>>>> +            MachineState *ms = MACHINE(qdev_get_machine());
>>>
>>> MachineState *ms = current_machine;
>>> ?
>>>
>>>
>>>> +            if (ms->smp.max_cpus > 1) {
>>>> +                parallel_cpus = true;
>>>> +            }
>>>> +        }
>>>>      }
>>>>  
>>>>      if (qemu_tcg_mttcg_enabled() || !single_tcg_cpu_thread) {
>>>> @@ -1904,7 +1914,6 @@ static void qemu_tcg_init_vcpu(CPUState *cpu)
>>>>  
>>>>          if (qemu_tcg_mttcg_enabled()) {
>>>>              /* create a thread per vCPU with TCG (MTTCG) */
>>>> -            parallel_cpus = true;
>>>>              snprintf(thread_name, VCPU_THREAD_NAME_SIZE, "CPU %d/TCG",
>>>>                   cpu->cpu_index);
>>>>  
>>>>
>>>
>>>
> 
>