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

[Philippe Mathieu-Daudé]

On 9/10/20 10:28 AM, Claudio Fontana wrote:
> Hi Philippe,
> 
> On 9/8/20 9:56 AM, Philippe Mathieu-Daudé wrote:
>> +Laurent
>>
>> On 9/8/20 9:09 AM, Claudio Fontana wrote:
>>> 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 .
>>
>> Better send a patch to prove your point :)
> 
> Yes, I am already testing without problems the cpus-refactoring series with 
> this applied:
> 
> commit 53f6db772f1522025650441102b16be17773bdc9
> Author: Claudio Fontana <cfontana@suse.de>
> Date:   Tue Sep 8 10:59:07 2020 +0200
> 
>     accel/tcg: use current_machine as it is always set for softmmu
>     
>     current_machine is always set before accelerators are initialized,
>     so use that instead of MACHINE(qdev_get_machine()).
>     
>     Signed-off-by: Claudio Fontana <cfontana@suse.de>
> 
> diff --git a/accel/tcg/tcg-cpus.c b/accel/tcg/tcg-cpus.c
> index ec7158b55e..05af1168a2 100644
> --- a/accel/tcg/tcg-cpus.c
> +++ b/accel/tcg/tcg-cpus.c
> @@ -484,7 +484,7 @@ static void tcg_start_vcpu_thread(CPUState *cpu)
>           * 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;
>              }
> 
> 
> 
>>
>> I have bad remember about the last time I tried to understand/modify
>> that part, because IIRC the user-mode creates some fake machine to
>> satisfy various QEMU generic code assumptions. Sincerely I now prefer
>> stay away from this; too many unmerged patches there.
> 
> 
> linux-user/main.c and bsd-user/main.c seem to use cpu_create() to create the 
> cpus,
> then they have their own cpu_loop(), they do not use any of the cpus.c code.
> 
> By contrast, softmmu/vl.c initializes current_machine in qemu_init(),
> even before accelerator is chosen and configured.
> 
> So there is no chance currently that current_machine is not set correctly when
> the accelerator vcpu startup code in is called.

Thanks for checking and correcting me!

We are good then :)

> 
> Ciao,
> 
> CLaudio