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

Michael Ellerman
2020-07-09T10:51:06Z

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?

> 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?

> 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