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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210118123451.1452206-1-npiggin@gmail.com

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 107bb4319e0e069547801826ae8b1dd3341f487b..eebb4a8c156caddc834f5b37ae51373b6a1a5e3a 100644 (file)
--- 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