[PATCH v2] powerpc: always enable queued spinlocks for 64s, disable for others

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@gmail.com>
---
Since v1, made the condition simpler as suggested by Christophe.
Verified this works as expected for a bunch of old configs
(e.g., updates old !EXPERT configs to PPC_QUEUED_SPINLOCKS=y if they
were previously =n).

Thanks,
Nick

 arch/powerpc/Kconfig | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 107bb4319e0e..eebb4a8c156c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -505,18 +505,14 @@ config HOTPLUG_CPU
 	  Say N if you are unsure.
 
 config PPC_QUEUED_SPINLOCKS
-	bool "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

-- 
2.23.0

On Mon, 18 Jan 2021 22:34:51 +1000, Nicholas Piggin wrote:

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.

Applied to powerpc/next.

[1/1] powerpc: Always enable queued spinlocks for 64s, disable for others
      https://git.kernel.org/powerpc/c/c9f3401313a5089f100d7d1ef4b75cd7b49b2190

cheers