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

[Claudio Fontana]

On 9/7/20 6:49 PM, Philippe Mathieu-Daudé wrote:
> 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 Philippe,

then why does the patch change softmmu/cpus.c in a way that accounts for user 
mode?

The function that the patch changes is never called in user mode.

The patch could instead use current_machine without any concern of it being 
NULL, it will always be set in vl.c .

Ciao,

Claudio

> 
>>
>> 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);
>>>>>  
>>>>>
>>>>
>>>>
>>
>>