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

Nicholas Piggin
2020-07-06T04:36:17Z

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
+ 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