[v2,10/10] riscv: Add qspinlock support based on Zabha extension

Commit Message

Alexandre Ghiti June 26, 2024, 1:03 p.m. UTC

In order to produce a generic kernel, a user can select
CONFIG_COMBO_SPINLOCKS which will fallback at runtime to the ticket
spinlock implementation if Zabha is not present.

Note that we can't use alternatives here because the discovery of
extensions is done too late and we need to start with the qspinlock
implementation because the ticket spinlock implementation would pollute
the spinlock value, so let's use static keys.

This is largely based on Guo's work and Leonardo reviews at [1].

Link: https://lore.kernel.org/linux-riscv/[e-mail]/ [1]
Signed-off-by: Alexandre Ghiti <[e-mail]>
---
 .../locking/queued-spinlocks/arch-support.txt |  2 +-
 arch/riscv/Kconfig                            | 10 +++++
 arch/riscv/include/asm/Kbuild                 |  4 +-
 arch/riscv/include/asm/spinlock.h             | 39 +++++++++++++++++++
 arch/riscv/kernel/setup.c                     | 21 ++++++++++
 include/asm-generic/qspinlock.h               |  2 +
 include/asm-generic/ticket_spinlock.h         |  2 +
 7 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/include/asm/spinlock.h

Comments

Andrea Parri June 27, 2024, 3:19 p.m. UTC | #1

> This is largely based on Guo's work and Leonardo reviews at [1].

Guo, could/should this have your Co-developed-by:/Signed-off-by:?

(disclaimer: I haven't looked at the last three patches of this submission
with due calm and probably won't before ~mid-July...)


> Link: https://lore.kernel.org/linux-riscv/[e-mail]/ [1]

There seems to be a distinct lack of experimental results, compared to the
previous/cited submission (and numbers are good to have!!  ;-)). Maybe Guo
/others can provide some? to confirm this is going in the right direction.

  Andrea

Patch

diff --git a/Documentation/features/locking/queued-spinlocks/arch-support.txt b/Documentation/features/locking/queued-spinlocks/arch-support.txt
index 22f2990392ff..cf26042480e2 100644
--- a/Documentation/features/locking/queued-spinlocks/arch-support.txt
+++ b/Documentation/features/locking/queued-spinlocks/arch-support.txt
@@ -20,7 +20,7 @@ 
     |    openrisc: |  ok  |
     |      parisc: | TODO |
     |     powerpc: |  ok  |
-    |       riscv: | TODO |
+    |       riscv: |  ok  |
     |        s390: | TODO |
     |          sh: | TODO |
     |       sparc: |  ok  |
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 0bbaec0444d0..c2ba673e58ca 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -72,6 +72,7 @@  config RISCV
 	select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE
+	select ARCH_WEAK_RELEASE_ACQUIRE if ARCH_USE_QUEUED_SPINLOCKS
 	select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU
 	select BUILDTIME_TABLE_SORT if MMU
 	select CLINT_TIMER if RISCV_M_MODE
@@ -482,6 +483,15 @@  config NODES_SHIFT
 	  Specify the maximum number of NUMA Nodes available on the target
 	  system.  Increases memory reserved to accommodate various tables.
 
+config RISCV_COMBO_SPINLOCKS
+	bool "Using combo spinlock"
+	depends on SMP && MMU && TOOLCHAIN_HAS_ZABHA
+	select ARCH_USE_QUEUED_SPINLOCKS
+	default y
+	help
+	  Embed both queued spinlock and ticket lock so that the spinlock
+	  implementation can be chosen at runtime.
+
 config RISCV_ALTERNATIVE
 	bool
 	depends on !XIP_KERNEL
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 504f8b7e72d4..ad72f2bd4cc9 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -2,10 +2,12 @@ 
 generic-y += early_ioremap.h
 generic-y += flat.h
 generic-y += kvm_para.h
+generic-y += mcs_spinlock.h
 generic-y += parport.h
-generic-y += spinlock.h
 generic-y += spinlock_types.h
+generic-y += ticket_spinlock.h
 generic-y += qrwlock.h
 generic-y += qrwlock_types.h
+generic-y += qspinlock.h
 generic-y += user.h
 generic-y += vmlinux.lds.h
diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
new file mode 100644
index 000000000000..4856d50006f2
--- /dev/null
+++ b/arch/riscv/include/asm/spinlock.h
@@ -0,0 +1,39 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_RISCV_SPINLOCK_H
+#define __ASM_RISCV_SPINLOCK_H
+
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+#define _Q_PENDING_LOOPS	(1 << 9)
+
+#define __no_arch_spinlock_redefine
+#include <asm/ticket_spinlock.h>
+#include <asm/qspinlock.h>
+#include <asm/alternative.h>
+
+DECLARE_STATIC_KEY_TRUE(qspinlock_key);
+
+#define SPINLOCK_BASE_DECLARE(op, type, type_lock)			\
+static __always_inline type arch_spin_##op(type_lock lock)		\
+{									\
+	if (static_branch_unlikely(&qspinlock_key))			\
+		return queued_spin_##op(lock);				\
+	return ticket_spin_##op(lock);					\
+}
+
+SPINLOCK_BASE_DECLARE(lock, void, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(unlock, void, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(is_locked, int, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(is_contended, int, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(trylock, bool, arch_spinlock_t *)
+SPINLOCK_BASE_DECLARE(value_unlocked, int, arch_spinlock_t)
+
+#else
+
+#include <asm/ticket_spinlock.h>
+
+#endif
+
+#include <asm/qrwlock.h>
+
+#endif /* __ASM_RISCV_SPINLOCK_H */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 4f73c0ae44b2..929bccd4c9e5 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -244,6 +244,26 @@  static void __init parse_dtb(void)
 #endif
 }
 
+DEFINE_STATIC_KEY_TRUE(qspinlock_key);
+EXPORT_SYMBOL(qspinlock_key);
+
+static void __init riscv_spinlock_init(void)
+{
+	asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, RISCV_ISA_EXT_ZACAS, 1)
+		 : : : : no_zacas);
+	asm goto(ALTERNATIVE("nop", "j %[qspinlock]", 0, RISCV_ISA_EXT_ZABHA, 1)
+		 : : : : qspinlock);
+
+no_zacas:
+	static_branch_disable(&qspinlock_key);
+	pr_info("Ticket spinlock: enabled\n");
+
+	return;
+
+qspinlock:
+	pr_info("Queued spinlock: enabled\n");
+}
+
 extern void __init init_rt_signal_env(void);
 
 void __init setup_arch(char **cmdline_p)
@@ -295,6 +315,7 @@  void __init setup_arch(char **cmdline_p)
 	riscv_set_dma_cache_alignment();
 
 	riscv_user_isa_enable();
+	riscv_spinlock_init();
 }
 
 bool arch_cpu_is_hotpluggable(int cpu)
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 0655aa5b57b2..bf47cca2c375 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -136,6 +136,7 @@  static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 }
 #endif
 
+#ifndef __no_arch_spinlock_redefine
 /*
  * Remapping spinlock architecture specific functions to the corresponding
  * queued spinlock functions.
@@ -146,5 +147,6 @@  static __always_inline bool virt_spin_lock(struct qspinlock *lock)
 #define arch_spin_lock(l)		queued_spin_lock(l)
 #define arch_spin_trylock(l)		queued_spin_trylock(l)
 #define arch_spin_unlock(l)		queued_spin_unlock(l)
+#endif
 
 #endif /* __ASM_GENERIC_QSPINLOCK_H */
diff --git a/include/asm-generic/ticket_spinlock.h b/include/asm-generic/ticket_spinlock.h
index cfcff22b37b3..325779970d8a 100644
--- a/include/asm-generic/ticket_spinlock.h
+++ b/include/asm-generic/ticket_spinlock.h
@@ -89,6 +89,7 @@  static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock)
 	return (s16)((val >> 16) - (val & 0xffff)) > 1;
 }
 
+#ifndef __no_arch_spinlock_redefine
 /*
  * Remapping spinlock architecture specific functions to the corresponding
  * ticket spinlock functions.
@@ -99,5 +100,6 @@  static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock)
 #define arch_spin_lock(l)		ticket_spin_lock(l)
 #define arch_spin_trylock(l)		ticket_spin_trylock(l)
 #define arch_spin_unlock(l)		ticket_spin_unlock(l)
+#endif
 
 #endif /* __ASM_GENERIC_TICKET_SPINLOCK_H */