From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
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 <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
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
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;
--
2.36.1
