Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

Waiman Long
2020-07-09T16:06:21Z

On 7/9/20 6:53 AM, Michael Ellerman wrote:
> Nicholas Piggin <npiggin@gmail.com> writes:
>
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>> arch/powerpc/include/asm/paravirt.h | 28 ++++++++
>> arch/powerpc/include/asm/qspinlock.h | 66 +++++++++++++++++++
>> arch/powerpc/include/asm/qspinlock_paravirt.h | 7 ++
>> arch/powerpc/platforms/pseries/Kconfig | 5 ++
>> arch/powerpc/platforms/pseries/setup.c | 6 +-
>> include/asm-generic/qspinlock.h | 2 +
> Another ack?
>
I am OK with adding the #ifdef around queued_spin_lock().

Acked-by: Waiman Long <longman@redhat.com>

>> diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
>> index 7a8546660a63..f2d51f929cf5 100644
>> --- a/arch/powerpc/include/asm/paravirt.h
>> +++ b/arch/powerpc/include/asm/paravirt.h
>> @@ -45,6 +55,19 @@ static inline void yield_to_preempted(int cpu, u32 yield_count)
>> {
>> ___bad_yield_to_preempted(); /* This would be a bug */
>> }
>> +
>> +extern void ___bad_yield_to_any(void);
>> +static inline void yield_to_any(void)
>> +{
>> + ___bad_yield_to_any(); /* This would be a bug */
>> +}
> Why do we do that rather than just not defining yield_to_any() at all
> and letting the build fail on that?
>
> There's a condition somewhere that we know will false at compile time
> and drop the call before linking?
>
>> diff --git a/arch/powerpc/include/asm/qspinlock_paravirt.h b/arch/powerpc/include/asm/qspinlock_paravirt.h
>> new file mode 100644
>> index 000000000000..750d1b5e0202
>> --- /dev/null
>> +++ b/arch/powerpc/include/asm/qspinlock_paravirt.h
>> @@ -0,0 +1,7 @@
>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> +#ifndef __ASM_QSPINLOCK_PARAVIRT_H
>> +#define __ASM_QSPINLOCK_PARAVIRT_H
> _ASM_POWERPC_QSPINLOCK_PARAVIRT_H please.
>
>> +
>> +EXPORT_SYMBOL(__pv_queued_spin_unlock);
> Why's that in a header? Should that (eventually) go with the generic implementation?
The PV qspinlock implementation is not that generic at the moment. Even
though native qspinlock is used by a number of archs, PV qspinlock is
only currently used in x86. This is certainly an area that needs
improvement.
>> diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
>> index 24c18362e5ea..756e727b383f 100644
>> --- a/arch/powerpc/platforms/pseries/Kconfig
>> +++ b/arch/powerpc/platforms/pseries/Kconfig
>> @@ -25,9 +25,14 @@ config PPC_PSERIES
>> select SWIOTLB
>> default y
>>
>> +config PARAVIRT_SPINLOCKS
>> + bool
>> + default n
> default n is the default.
>
>> diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
>> index 2db8469e475f..747a203d9453 100644
>> --- a/arch/powerpc/platforms/pseries/setup.c
>> +++ b/arch/powerpc/platforms/pseries/setup.c
>> @@ -771,8 +771,12 @@ static void __init pSeries_setup_arch(void)
>> if (firmware_has_feature(FW_FEATURE_LPAR)) {
>> vpa_init(boot_cpuid);
>>
>> - if (lppaca_shared_proc(get_lppaca()))
>> + if (lppaca_shared_proc(get_lppaca())) {
>> static_branch_enable(&shared_processor);
>> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>> + pv_spinlocks_init();
>> +#endif
>> + }
> We could avoid the ifdef with this I think?
>
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 434615f1d761..6ec72282888d 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -10,5 +10,9 @@
> #include <asm/simple_spinlock.h>
> #endif
>
> +#ifndef CONFIG_PARAVIRT_SPINLOCKS
> +static inline void pv_spinlocks_init(void) { }
> +#endif
> +
> #endif /* __KERNEL__ */
> #endif /* __ASM_SPINLOCK_H */
>
>
> cheers
>
We don't really need to do a pv_spinlocks_init() if pv_kick() isn't
supported.

Cheers,
Longman