[V8,08/10] riscv: Add combo spinlock support

Commit Message

Guo Ren July 24, 2022, 12:25 p.m. UTC

From: Guo Ren <[e-mail]>

Combo spinlock could support queued and ticket in one Linux Image and
select them during boot time with command line option. Here is the
func-size(Bytes) comparison table below:

TYPE			: COMBO | TICKET | QUEUED
arch_spin_lock		: 106	| 60     | 50
arch_spin_unlock	: 54    | 36     | 26
arch_spin_trylock	: 110   | 72     | 54
arch_spin_is_locked	: 48    | 34     | 20
arch_spin_is_contended	: 56    | 40     | 24
rch_spin_value_unlocked	: 48    | 34     | 24

One example of disassemble combo arch_spin_unlock:
   0xffffffff8000409c <+14>:    nop # jump label slot
   0xffffffff800040a0 <+18>:    fence   rw,w # queued spinlock start
   0xffffffff800040a4 <+22>:    sb      zero,0(a4) # queued spinlock end
   0xffffffff800040a8 <+26>:    ld      s0,8(sp)
   0xffffffff800040aa <+28>:    addi    sp,sp,16
   0xffffffff800040ac <+30>:    ret
   0xffffffff800040ae <+32>:    lw      a5,0(a4) # ticket spinlock start
   0xffffffff800040b0 <+34>:    sext.w  a5,a5
   0xffffffff800040b2 <+36>:    fence   rw,w
   0xffffffff800040b6 <+40>:    addiw   a5,a5,1
   0xffffffff800040b8 <+42>:    slli    a5,a5,0x30
   0xffffffff800040ba <+44>:    srli    a5,a5,0x30
   0xffffffff800040bc <+46>:    sh      a5,0(a4) # ticket spinlock end
   0xffffffff800040c0 <+50>:    ld      s0,8(sp)
   0xffffffff800040c2 <+52>:    addi    sp,sp,16
   0xffffffff800040c4 <+54>:    ret

We could see queued spinlock is better than ticket-lock when there is no
contend into queued_spin_lock_slowpath. And combo could provide a
compatible Linux Image for a different kind of micro-arch design.

Signed-off-by: Guo Ren <[e-mail]>
Signed-off-by: Guo Ren <[e-mail]>
---
 arch/riscv/Kconfig                |  9 +++-
 arch/riscv/include/asm/Kbuild     |  1 -
 arch/riscv/include/asm/spinlock.h | 77 +++++++++++++++++++++++++++++++
 arch/riscv/kernel/setup.c         | 22 +++++++++
 4 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/include/asm/spinlock.h

Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 721f098228a8..f1d68491a1cf 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -361,7 +361,7 @@  config NODES_SHIFT
 
 choice
 	prompt "RISC-V spinlock type"
-	default RISCV_TICKET_SPINLOCKS
+	default RISCV_COMBO_SPINLOCKS
 
 config RISCV_TICKET_SPINLOCKS
 	bool "Using ticket spinlock"
@@ -373,6 +373,13 @@  config RISCV_QUEUED_SPINLOCKS
 	help
 	  Make sure your micro arch LL/SC has a strong forward progress guarantee.
 	  Otherwise, stay at ticket-lock/combo-lock.
+
+config RISCV_COMBO_SPINLOCKS
+	bool "Using combo spinlock"
+	depends on SMP && MMU
+	select ARCH_USE_QUEUED_SPINLOCKS
+	help
+	  Select queued spinlock or ticket-lock with jump_label.
 endchoice
 
 config RISCV_ALTERNATIVE
diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild
index 2cce98c7b653..59d5ea7390ea 100644
--- a/arch/riscv/include/asm/Kbuild
+++ b/arch/riscv/include/asm/Kbuild
@@ -5,7 +5,6 @@  generic-y += kvm_para.h
 generic-y += mcs_spinlock.h
 generic-y += parport.h
 generic-y += qspinlock.h
-generic-y += spinlock.h
 generic-y += spinlock_types.h
 generic-y += qrwlock.h
 generic-y += qrwlock_types.h
diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
new file mode 100644
index 000000000000..b079462d818b
--- /dev/null
+++ b/arch/riscv/include/asm/spinlock.h
@@ -0,0 +1,77 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_RISCV_SPINLOCK_H
+#define __ASM_RISCV_SPINLOCK_H
+
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+#include <asm-generic/ticket_spinlock.h>
+
+#undef arch_spin_is_locked
+#undef arch_spin_is_contended
+#undef arch_spin_value_unlocked
+#undef arch_spin_lock
+#undef arch_spin_trylock
+#undef arch_spin_unlock
+
+#include <asm-generic/qspinlock.h>
+#include <linux/jump_label.h>
+
+#undef arch_spin_is_locked
+#undef arch_spin_is_contended
+#undef arch_spin_value_unlocked
+#undef arch_spin_lock
+#undef arch_spin_trylock
+#undef arch_spin_unlock
+
+DECLARE_STATIC_KEY_TRUE(qspinlock_key);
+
+static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		queued_spin_lock(lock);
+	else
+		ticket_spin_lock(lock);
+}
+
+static __always_inline bool arch_spin_trylock(arch_spinlock_t *lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		return queued_spin_trylock(lock);
+	return ticket_spin_trylock(lock);
+}
+
+static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		queued_spin_unlock(lock);
+	else
+		ticket_spin_unlock(lock);
+}
+
+static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		return queued_spin_value_unlocked(lock);
+	else
+		return ticket_spin_value_unlocked(lock);
+}
+
+static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		return queued_spin_is_locked(lock);
+	return ticket_spin_is_locked(lock);
+}
+
+static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
+{
+	if (static_branch_likely(&qspinlock_key))
+		return queued_spin_is_contended(lock);
+	return ticket_spin_is_contended(lock);
+}
+#include <asm/qrwlock.h>
+#else
+#include <asm-generic/spinlock.h>
+#endif /* CONFIG_RISCV_COMBO_SPINLOCKS */
+
+#endif /* __ASM_RISCV_SPINLOCK_H */
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index f0f36a4a0e9b..b763039bf49b 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -261,6 +261,13 @@  static void __init parse_dtb(void)
 #endif
 }
 
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+DEFINE_STATIC_KEY_TRUE_RO(qspinlock_key);
+EXPORT_SYMBOL(qspinlock_key);
+
+static bool qspinlock_flag __initdata = false;
+#endif
+
 void __init setup_arch(char **cmdline_p)
 {
 	parse_dtb();
@@ -295,10 +302,25 @@  void __init setup_arch(char **cmdline_p)
 	setup_smp();
 #endif
 
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+	if (!qspinlock_flag)
+		static_branch_disable(&qspinlock_key);
+#endif
+
 	riscv_fill_hwcap();
 	apply_boot_alternatives();
 }
 
+#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
+static int __init enable_qspinlock(char *p)
+{
+	qspinlock_flag = true;
+
+	return 0;
+}
+early_param("qspinlock", enable_qspinlock);
+#endif
+
 static int __init topology_init(void)
 {
 	int i, ret;