Re: [PATCH v2 3/6] powerpc/smp: Move shared_processor static key to smp.h

Re: [PATCH v2 3/6] powerpc/smp: Move shared_processor static key to smp.h

[Michael Ellerman]

Srikar Dronamraju <srikar@linux.vnet.ibm.com> writes:
> The ability to detect if the system is running in a shared processor
> mode is helpful in few more generic cases not just in
> paravirtualization.
> For example: At boot time, different scheduler/ topology flags may be
> set based on the processor mode. Hence move it to a more generic file.

I'd rather you just included paravirt.h in the few files where you need it.

cheers

> diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
> index 0372b0093f72..cf83e837a571 100644
> --- a/arch/powerpc/include/asm/paravirt.h
> +++ b/arch/powerpc/include/asm/paravirt.h
> @@ -15,13 +15,6 @@
>  #include <asm/kvm_guest.h>
>  #include <asm/cputhreads.h>
>  
> -DECLARE_STATIC_KEY_FALSE(shared_processor);
> -
> -static inline bool is_shared_processor(void)
> -{
> -	return static_branch_unlikely(&shared_processor);
> -}
> -
>  #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
>  extern struct static_key paravirt_steal_enabled;
>  extern struct static_key paravirt_steal_rq_enabled;
> @@ -77,11 +70,6 @@ static inline bool is_vcpu_idle(int vcpu)
>  	return lppaca_of(vcpu).idle;
>  }
>  #else
> -static inline bool is_shared_processor(void)
> -{
> -	return false;
> -}
> -
>  static inline u32 yield_count_of(int cpu)
>  {
>  	return 0;
> diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
> index aaaa576d0e15..08631b2a4528 100644
> --- a/arch/powerpc/include/asm/smp.h
> +++ b/arch/powerpc/include/asm/smp.h
> @@ -34,6 +34,20 @@ extern bool coregroup_enabled;
>  extern int cpu_to_chip_id(int cpu);
>  extern int *chip_id_lookup_table;
>  
> +#ifdef CONFIG_PPC_SPLPAR
> +DECLARE_STATIC_KEY_FALSE(shared_processor);
> +
> +static inline bool is_shared_processor(void)
> +{
> +	return static_branch_unlikely(&shared_processor);
> +}
> +#else
> +static inline bool is_shared_processor(void)
> +{
> +	return false;
> +}
> +#endif
> +
>  DECLARE_PER_CPU(cpumask_var_t, thread_group_l1_cache_map);
>  DECLARE_PER_CPU(cpumask_var_t, thread_group_l2_cache_map);
>  DECLARE_PER_CPU(cpumask_var_t, thread_group_l3_cache_map);
> -- 
> 2.31.1
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Re: [PATCH v2 3/6] powerpc/smp: Move shared_processor static key to smp.h

[Michael Ellerman]

Srikar Dronamraju <srikar@linux.vnet.ibm.com> writes:
> * Michael Ellerman <mpe@ellerman.id.au> [2023-10-19 15:41:40]:
>
>> Srikar Dronamraju <srikar@linux.vnet.ibm.com> writes:
>> > The ability to detect if the system is running in a shared processor
>> > mode is helpful in few more generic cases not just in
>> > paravirtualization.
>> > For example: At boot time, different scheduler/ topology flags may be
>> > set based on the processor mode. Hence move it to a more generic file.
>> 
>> I'd rather you just included paravirt.h in the few files where you need it.
>
> I thought, detecting if a Processor was shared or not was more a
> smp/processor related than a paravirt related.

It's both really :)

It's definitely paravirt related though, because if we weren't
*para*virt then we wouldn't know there was a hypervisor at all :)

But having smaller more focused headers is preferable in general just
for mechanical reasons.

cheers
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