Re: [PATCH v3 4/6] powerpc/64s: implement queued spinlocks and rwlocks

["Michal Suchánek" <msuchanek@suse.de>]

On Mon, Jul 06, 2020 at 02:35:38PM +1000, Nicholas Piggin wrote:
> These have shown significantly improved performance and fairness when
> spinlock contention is moderate to high on very large systems.
> 
>  [ Numbers hopefully forthcoming after more testing, but initial
>    results look good ]
> 
> Thanks to the fast path, single threaded performance is not noticably
> hurt.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/Kconfig                      | 13 ++++++++++++
>  arch/powerpc/include/asm/Kbuild           |  2 ++
>  arch/powerpc/include/asm/qspinlock.h      | 25 +++++++++++++++++++++++
>  arch/powerpc/include/asm/spinlock.h       |  5 +++++
>  arch/powerpc/include/asm/spinlock_types.h |  5 +++++
>  arch/powerpc/lib/Makefile                 |  3 +++
>  include/asm-generic/qspinlock.h           |  2 ++
>  7 files changed, 55 insertions(+)
>  create mode 100644 arch/powerpc/include/asm/qspinlock.h
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 24ac85c868db..17663ea57697 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -146,6 +146,8 @@ config PPC
>  	select ARCH_SUPPORTS_ATOMIC_RMW
>  	select ARCH_USE_BUILTIN_BSWAP
>  	select ARCH_USE_CMPXCHG_LOCKREF		if PPC64
> +	select ARCH_USE_QUEUED_RWLOCKS		if PPC_QUEUED_SPINLOCKS
> +	select ARCH_USE_QUEUED_SPINLOCKS	if PPC_QUEUED_SPINLOCKS
>  	select ARCH_WANT_IPC_PARSE_VERSION
>  	select ARCH_WEAK_RELEASE_ACQUIRE
>  	select BINFMT_ELF
> @@ -492,6 +494,17 @@ config HOTPLUG_CPU
>  
>  	  Say N if you are unsure.
>  
> +config PPC_QUEUED_SPINLOCKS
> +	bool "Queued spinlocks"
> +	depends on SMP
> +	default "y" if PPC_BOOK3S_64
> +	help
> +	  Say Y here to use to use queued spinlocks which are more complex
> +	  but give better salability and fairness on large SMP and NUMA
                           ^ +c?
Thanks

Michal
> +	  systems.
> +
> +	  If unsure, say "Y" if you have lots of cores, otherwise "N".
> +
>  config ARCH_CPU_PROBE_RELEASE
>  	def_bool y
>  	depends on HOTPLUG_CPU
> diff --git a/arch/powerpc/include/asm/Kbuild b/arch/powerpc/include/asm/Kbuild
> index dadbcf3a0b1e..1dd8b6adff5e 100644
> --- a/arch/powerpc/include/asm/Kbuild
> +++ b/arch/powerpc/include/asm/Kbuild
> @@ -6,5 +6,7 @@ generated-y += syscall_table_spu.h
>  generic-y += export.h
>  generic-y += local64.h
>  generic-y += mcs_spinlock.h
> +generic-y += qrwlock.h
> +generic-y += qspinlock.h
>  generic-y += vtime.h
>  generic-y += early_ioremap.h
> diff --git a/arch/powerpc/include/asm/qspinlock.h b/arch/powerpc/include/asm/qspinlock.h
> new file mode 100644
> index 000000000000..c49e33e24edd
> --- /dev/null
> +++ b/arch/powerpc/include/asm/qspinlock.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_POWERPC_QSPINLOCK_H
> +#define _ASM_POWERPC_QSPINLOCK_H
> +
> +#include <asm-generic/qspinlock_types.h>
> +
> +#define _Q_PENDING_LOOPS	(1 << 9) /* not tuned */
> +
> +#define smp_mb__after_spinlock()   smp_mb()
> +
> +static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
> +{
> +	/*
> +	 * This barrier was added to simple spinlocks by commit 51d7d5205d338,
> +	 * but it should now be possible to remove it, asm arm64 has done with
> +	 * commit c6f5d02b6a0f.
> +	 */
> +	smp_mb();
> +	return atomic_read(&lock->val);
> +}
> +#define queued_spin_is_locked queued_spin_is_locked
> +
> +#include <asm-generic/qspinlock.h>
> +
> +#endif /* _ASM_POWERPC_QSPINLOCK_H */
> diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
> index 21357fe05fe0..434615f1d761 100644
> --- a/arch/powerpc/include/asm/spinlock.h
> +++ b/arch/powerpc/include/asm/spinlock.h
> @@ -3,7 +3,12 @@
>  #define __ASM_SPINLOCK_H
>  #ifdef __KERNEL__
>  
> +#ifdef CONFIG_PPC_QUEUED_SPINLOCKS
> +#include <asm/qspinlock.h>
> +#include <asm/qrwlock.h>
> +#else
>  #include <asm/simple_spinlock.h>
> +#endif
>  
>  #endif /* __KERNEL__ */
>  #endif /* __ASM_SPINLOCK_H */
> diff --git a/arch/powerpc/include/asm/spinlock_types.h b/arch/powerpc/include/asm/spinlock_types.h
> index 3906f52dae65..c5d742f18021 100644
> --- a/arch/powerpc/include/asm/spinlock_types.h
> +++ b/arch/powerpc/include/asm/spinlock_types.h
> @@ -6,6 +6,11 @@
>  # error "please don't include this file directly"
>  #endif
>  
> +#ifdef CONFIG_PPC_QUEUED_SPINLOCKS
> +#include <asm-generic/qspinlock_types.h>
> +#include <asm-generic/qrwlock_types.h>
> +#else
>  #include <asm/simple_spinlock_types.h>
> +#endif
>  
>  #endif
> diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> index 5e994cda8e40..d66a645503eb 100644
> --- a/arch/powerpc/lib/Makefile
> +++ b/arch/powerpc/lib/Makefile
> @@ -41,7 +41,10 @@ obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
>  obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
>  	   memcpy_64.o memcpy_mcsafe_64.o
>  
> +ifndef CONFIG_PPC_QUEUED_SPINLOCKS
>  obj64-$(CONFIG_SMP)	+= locks.o
> +endif
> +
>  obj64-$(CONFIG_ALTIVEC)	+= vmx-helper.o
>  obj64-$(CONFIG_KPROBES_SANITY_TEST)	+= test_emulate_step.o \
>  					   test_emulate_step_exec_instr.o
> diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
> index fde943d180e0..fb0a814d4395 100644
> --- a/include/asm-generic/qspinlock.h
> +++ b/include/asm-generic/qspinlock.h
> @@ -12,6 +12,7 @@
>  
>  #include <asm-generic/qspinlock_types.h>
>  
> +#ifndef queued_spin_is_locked
>  /**
>   * queued_spin_is_locked - is the spinlock locked?
>   * @lock: Pointer to queued spinlock structure
> @@ -25,6 +26,7 @@ static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
>  	 */
>  	return atomic_read(&lock->val);
>  }
> +#endif
>  
>  /**
>   * queued_spin_value_unlocked - is the spinlock structure unlocked?
> -- 
> 2.23.0
>