MIPS: Use queued spinlocks (qspinlock)

This patch switches MIPS to make use of generically implemented queued
spinlocks, rather than the ticket spinlocks used previously. This allows
us to drop a whole load of inline assembly, share more generic code, and
is also a performance win.

Results from running the AIM7 short workload on a MIPS Creator Ci40 (ie.
2 core 2 thread interAptiv CPU clocked at 546MHz) with v4.12-rc4
pistachio_defconfig, with ftrace disabled due to a current bug, and both
with & without use of queued rwlocks & spinlocks:

  Forks | v4.12-rc4 | +qlocks  | Change
 -------|-----------|----------|--------
     10 | 52630.32  | 53316.31 | +1.01%
     20 | 51777.80  | 52623.15 | +1.02%
     30 | 51645.92  | 52517.26 | +1.02%
     40 | 51634.88  | 52419.89 | +1.02%
     50 | 51506.75  | 52307.81 | +1.02%
     60 | 51500.74  | 52322.72 | +1.02%
     70 | 51434.81  | 52288.60 | +1.02%
     80 | 51423.22  | 52434.85 | +1.02%
     90 | 51428.65  | 52410.10 | +1.02%

The kernels used for these tests also had my "MIPS: Hardcode cpu_has_*
where known at compile time due to ISA" patch applied, which allows the
kernel_uses_llsc checks in cmpxchg() & xchg() to be optimised away at
compile time.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16358/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 7c2a64b..ef1cb20 100644 (file)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -12,6 +12,7 @@ config MIPS
        select ARCH_USE_BUILTIN_BSWAP
        select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
        select ARCH_USE_QUEUED_RWLOCKS
+       select ARCH_USE_QUEUED_SPINLOCKS
        select ARCH_WANT_IPC_PARSE_VERSION
        select BUILDTIME_EXTABLE_SORT
        select CLONE_BACKWARDS

diff --git a/arch/mips/include/asm/Kbuild b/arch/mips/include/asm/Kbuild
index ae6cb47..7c8aab2 100644 (file)
--- a/arch/mips/include/asm/Kbuild
+++ b/arch/mips/include/asm/Kbuild
@@ -13,6 +13,7 @@ generic-y += parport.h
 generic-y += percpu.h
 generic-y += preempt.h
 generic-y += qrwlock.h
+generic-y += qspinlock.h
 generic-y += sections.h
 generic-y += segment.h
 generic-y += serial.h

diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h
index 3e7afff..a7d21da 100644 (file)
--- a/arch/mips/include/asm/spinlock.h
+++ b/arch/mips/include/asm/spinlock.h
@@ -9,217 +9,9 @@
 #ifndef _ASM_SPINLOCK_H
 #define _ASM_SPINLOCK_H
 
-#include <linux/compiler.h>
-
-#include <asm/barrier.h>
 #include <asm/processor.h>
 #include <asm/qrwlock.h>
-#include <asm/compiler.h>
-#include <asm/war.h>
-
-/*
- * Your basic SMP spinlocks, allowing only a single CPU anywhere
- *
- * Simple spin lock operations.         There are two variants, one clears IRQ's
- * on the local processor, one does not.
- *
- * These are fair FIFO ticket locks
- *
- * (the type definitions are in asm/spinlock_types.h)
- */
-
-
-/*
- * Ticket locks are conceptually two parts, one indicating the current head of
- * the queue, and the other indicating the current tail. The lock is acquired
- * by atomically noting the tail and incrementing it by one (thus adding
- * ourself to the queue and noting our position), then waiting until the head
- * becomes equal to the the initial value of the tail.
- */
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
-       u32 counters = ACCESS_ONCE(lock->lock);
-
-       return ((counters >> 16) ^ counters) & 0xffff;
-}
-
-static inline int arch_spin_value_unlocked(arch_spinlock_t lock)
-{
-       return lock.h.serving_now == lock.h.ticket;
-}
-
-#define arch_spin_lock_flags(lock, flags) arch_spin_lock(lock)
-
-static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
-{
-       u16 owner = READ_ONCE(lock->h.serving_now);
-       smp_rmb();
-       for (;;) {
-               arch_spinlock_t tmp = READ_ONCE(*lock);
-
-               if (tmp.h.serving_now == tmp.h.ticket ||
-                   tmp.h.serving_now != owner)
-                       break;
-
-               cpu_relax();
-       }
-       smp_acquire__after_ctrl_dep();
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
-       u32 counters = ACCESS_ONCE(lock->lock);
-
-       return (((counters >> 16) - counters) & 0xffff) > 1;
-}
-#define arch_spin_is_contended arch_spin_is_contended
-
-static inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-       int my_ticket;
-       int tmp;
-       int inc = 0x10000;
-
-       if (R10000_LLSC_WAR) {
-               __asm__ __volatile__ (
-               "       .set push               # arch_spin_lock        \n"
-               "       .set noreorder                                  \n"
-               "                                                       \n"
-               "1:     ll      %[ticket], %[ticket_ptr]                \n"
-               "       addu    %[my_ticket], %[ticket], %[inc]         \n"
-               "       sc      %[my_ticket], %[ticket_ptr]             \n"
-               "       beqzl   %[my_ticket], 1b                        \n"
-               "        nop                                            \n"
-               "       srl     %[my_ticket], %[ticket], 16             \n"
-               "       andi    %[ticket], %[ticket], 0xffff            \n"
-               "       bne     %[ticket], %[my_ticket], 4f             \n"
-               "        subu   %[ticket], %[my_ticket], %[ticket]      \n"
-               "2:                                                     \n"
-               "       .subsection 2                                   \n"
-               "4:     andi    %[ticket], %[ticket], 0xffff            \n"
-               "       sll     %[ticket], 5                            \n"
-               "                                                       \n"
-               "6:     bnez    %[ticket], 6b                           \n"
-               "        subu   %[ticket], 1                            \n"
-               "                                                       \n"
-               "       lhu     %[ticket], %[serving_now_ptr]           \n"
-               "       beq     %[ticket], %[my_ticket], 2b             \n"
-               "        subu   %[ticket], %[my_ticket], %[ticket]      \n"
-               "       b       4b                                      \n"
-               "        subu   %[ticket], %[ticket], 1                 \n"
-               "       .previous                                       \n"
-               "       .set pop                                        \n"
-               : [ticket_ptr] "+" GCC_OFF_SMALL_ASM() (lock->lock),
-                 [serving_now_ptr] "+m" (lock->h.serving_now),
-                 [ticket] "=&r" (tmp),
-                 [my_ticket] "=&r" (my_ticket)
-               : [inc] "r" (inc));
-       } else {
-               __asm__ __volatile__ (
-               "       .set push               # arch_spin_lock        \n"
-               "       .set noreorder                                  \n"
-               "                                                       \n"
-               "1:     ll      %[ticket], %[ticket_ptr]                \n"
-               "       addu    %[my_ticket], %[ticket], %[inc]         \n"
-               "       sc      %[my_ticket], %[ticket_ptr]             \n"
-               "       beqz    %[my_ticket], 1b                        \n"
-               "        srl    %[my_ticket], %[ticket], 16             \n"
-               "       andi    %[ticket], %[ticket], 0xffff            \n"
-               "       bne     %[ticket], %[my_ticket], 4f             \n"
-               "        subu   %[ticket], %[my_ticket], %[ticket]      \n"
-               "2:     .insn                                           \n"
-               "       .subsection 2                                   \n"
-               "4:     andi    %[ticket], %[ticket], 0xffff            \n"
-               "       sll     %[ticket], 5                            \n"
-               "                                                       \n"
-               "6:     bnez    %[ticket], 6b                           \n"
-               "        subu   %[ticket], 1                            \n"
-               "                                                       \n"
-               "       lhu     %[ticket], %[serving_now_ptr]           \n"
-               "       beq     %[ticket], %[my_ticket], 2b             \n"
-               "        subu   %[ticket], %[my_ticket], %[ticket]      \n"
-               "       b       4b                                      \n"
-               "        subu   %[ticket], %[ticket], 1                 \n"
-               "       .previous                                       \n"
-               "       .set pop                                        \n"
-               : [ticket_ptr] "+" GCC_OFF_SMALL_ASM() (lock->lock),
-                 [serving_now_ptr] "+m" (lock->h.serving_now),
-                 [ticket] "=&r" (tmp),
-                 [my_ticket] "=&r" (my_ticket)
-               : [inc] "r" (inc));
-       }
-
-       smp_llsc_mb();
-}
-
-static inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-       unsigned int serving_now = lock->h.serving_now + 1;
-       wmb();
-       lock->h.serving_now = (u16)serving_now;
-       nudge_writes();
-}
-
-static inline unsigned int arch_spin_trylock(arch_spinlock_t *lock)
-{
-       int tmp, tmp2, tmp3;
-       int inc = 0x10000;
-
-       if (R10000_LLSC_WAR) {
-               __asm__ __volatile__ (
-               "       .set push               # arch_spin_trylock     \n"
-               "       .set noreorder                                  \n"
-               "                                                       \n"
-               "1:     ll      %[ticket], %[ticket_ptr]                \n"
-               "       srl     %[my_ticket], %[ticket], 16             \n"
-               "       andi    %[now_serving], %[ticket], 0xffff       \n"
-               "       bne     %[my_ticket], %[now_serving], 3f        \n"
-               "        addu   %[ticket], %[ticket], %[inc]            \n"
-               "       sc      %[ticket], %[ticket_ptr]                \n"
-               "       beqzl   %[ticket], 1b                           \n"
-               "        li     %[ticket], 1                            \n"
-               "2:                                                     \n"
-               "       .subsection 2                                   \n"
-               "3:     b       2b                                      \n"
-               "        li     %[ticket], 0                            \n"
-               "       .previous                                       \n"
-               "       .set pop                                        \n"
-               : [ticket_ptr] "+" GCC_OFF_SMALL_ASM() (lock->lock),
-                 [ticket] "=&r" (tmp),
-                 [my_ticket] "=&r" (tmp2),
-                 [now_serving] "=&r" (tmp3)
-               : [inc] "r" (inc));
-       } else {
-               __asm__ __volatile__ (
-               "       .set push               # arch_spin_trylock     \n"
-               "       .set noreorder                                  \n"
-               "                                                       \n"
-               "1:     ll      %[ticket], %[ticket_ptr]                \n"
-               "       srl     %[my_ticket], %[ticket], 16             \n"
-               "       andi    %[now_serving], %[ticket], 0xffff       \n"
-               "       bne     %[my_ticket], %[now_serving], 3f        \n"
-               "        addu   %[ticket], %[ticket], %[inc]            \n"
-               "       sc      %[ticket], %[ticket_ptr]                \n"
-               "       beqz    %[ticket], 1b                           \n"
-               "        li     %[ticket], 1                            \n"
-               "2:     .insn                                           \n"
-               "       .subsection 2                                   \n"
-               "3:     b       2b                                      \n"
-               "        li     %[ticket], 0                            \n"
-               "       .previous                                       \n"
-               "       .set pop                                        \n"
-               : [ticket_ptr] "+" GCC_OFF_SMALL_ASM() (lock->lock),
-                 [ticket] "=&r" (tmp),
-                 [my_ticket] "=&r" (tmp2),
-                 [now_serving] "=&r" (tmp3)
-               : [inc] "r" (inc));
-       }
-
-       smp_llsc_mb();
-
-       return tmp;
-}
+#include <asm/qspinlock.h>
 
 #define arch_read_lock_flags(lock, flags) arch_read_lock(lock)
 #define arch_write_lock_flags(lock, flags) arch_write_lock(lock)

diff --git a/arch/mips/include/asm/spinlock_types.h b/arch/mips/include/asm/spinlock_types.h
index 3d38bfa..177e722 100644 (file)
--- a/arch/mips/include/asm/spinlock_types.h
+++ b/arch/mips/include/asm/spinlock_types.h
@@ -1,29 +1,7 @@
 #ifndef _ASM_SPINLOCK_TYPES_H
 #define _ASM_SPINLOCK_TYPES_H
 
-#include <linux/types.h>
-
-#include <asm/byteorder.h>
-
-typedef union {
-       /*
-        * bits  0..15 : serving_now
-        * bits 16..31 : ticket
-        */
-       u32 lock;
-       struct {
-#ifdef __BIG_ENDIAN
-               u16 ticket;
-               u16 serving_now;
-#else
-               u16 serving_now;
-               u16 ticket;
-#endif
-       } h;
-} arch_spinlock_t;
-
-#define __ARCH_SPIN_LOCK_UNLOCKED      { .lock = 0 }
-
+#include <asm-generic/qspinlock_types.h>
 #include <asm-generic/qrwlock_types.h>
 
 #endif