[PATCH] powerpc: always enable queued spinlocks for 64s, disable for others

[Christophe Leroy]

Le 21/12/2020 à 04:22, Nicholas Piggin a écrit :
> Queued spinlocks have shown to have good performance and fairness
> properties even on smaller (2 socket) POWER systems. This selects
> them automatically for 64s. For other platforms they are de-selected,
> the standard spinlock is far simpler and smaller code, and single
> chips with a handful of cores is unlikely to show any improvement.
> 
> CONFIG_EXPERT still allows this to be changed, e.g., to help debug
> performance or correctness issues.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/Kconfig | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index ae7391627054..1f9f9e64d638 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -255,6 +255,7 @@ config PPC
>   	select PCI_MSI_ARCH_FALLBACKS		if PCI_MSI
>   	select PCI_SYSCALL			if PCI
>   	select PPC_DAWR				if PPC64
> +	select PPC_QUEUED_SPINLOCKS		if !EXPERT && PPC_BOOK3S_64 && SMP

The condition is a bit complicated, and it doesn't set it to Y by default when EXPERT is selected.

>   	select RTC_LIB
>   	select SPARSE_IRQ
>   	select SYSCTL_EXCEPTION_TRACE
> @@ -506,16 +507,13 @@ config HOTPLUG_CPU
>   config PPC_QUEUED_SPINLOCKS
>   	bool "Queued spinlocks"
>   	depends on SMP
> +	depends on EXPERT || PPC_BOOK3S_64
> +

I would do:

    config PPC_QUEUED_SPINLOCKS
  	bool "Queued spinlocks" if EXPERT
  	depends on SMP
	default PPC_BOOK3S_64



>   	help
>   	  Say Y here to use queued spinlocks which give better scalability and
>   	  fairness on large SMP and NUMA systems without harming single threaded
>   	  performance.
>   
> -	  This option is currently experimental, the code is more complex and
> -	  less tested so it defaults to "N" for the moment.
> -
> -	  If unsure, say "N".
> -
>   config ARCH_CPU_PROBE_RELEASE
>   	def_bool y
>   	depends on HOTPLUG_CPU
> 

Christophe