[v2,4/5] spinlock: reimplement with atomic one-way barrier builtins
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The __sync builtin based implementation generates full memory barriers
('dmb ish') on Arm platforms. Using C11 atomic builtins to generate one way
barriers.
Here is the assembly code of __sync_compare_and_swap builtin.
__sync_bool_compare_and_swap(dst, exp, src);
0x000000000090f1b0 <+16>: e0 07 40 f9 ldr x0, [sp, #8]
0x000000000090f1b4 <+20>: e1 0f 40 79 ldrh w1, [sp, #6]
0x000000000090f1b8 <+24>: e2 0b 40 79 ldrh w2, [sp, #4]
0x000000000090f1bc <+28>: 21 3c 00 12 and w1, w1, #0xffff
0x000000000090f1c0 <+32>: 03 7c 5f 48 ldxrh w3, [x0]
0x000000000090f1c4 <+36>: 7f 00 01 6b cmp w3, w1
0x000000000090f1c8 <+40>: 61 00 00 54 b.ne 0x90f1d4
<rte_atomic16_cmpset+52> // b.any
0x000000000090f1cc <+44>: 02 fc 04 48 stlxrh w4, w2, [x0]
0x000000000090f1d0 <+48>: 84 ff ff 35 cbnz w4, 0x90f1c0
<rte_atomic16_cmpset+32>
0x000000000090f1d4 <+52>: bf 3b 03 d5 dmb ish
0x000000000090f1d8 <+56>: e0 17 9f 1a cset w0, eq // eq = none
The benchmarking results showed 3X performance gain on Cavium ThunderX2 and
13% on Qualcomm Falmon and 3.7% on 4-A72 Marvell macchiatobin.
Here is the example test result on TX2:
*** spinlock_autotest without this patch ***
Core [123] Cost Time = 639822 us
Core [124] Cost Time = 633253 us
Core [125] Cost Time = 646030 us
Core [126] Cost Time = 643189 us
Core [127] Cost Time = 647039 us
Total Cost Time = 95433298 us
*** spinlock_autotest with this patch ***
Core [123] Cost Time = 163615 us
Core [124] Cost Time = 166471 us
Core [125] Cost Time = 189044 us
Core [126] Cost Time = 195745 us
Core [127] Cost Time = 78423 us
Total Cost Time = 27339656 us
Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
Reviewed-by: Steve Capper <Steve.Capper@arm.com>
---
lib/librte_eal/common/include/generic/rte_spinlock.h | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
@@ -61,9 +61,14 @@ rte_spinlock_lock(rte_spinlock_t *sl);
static inline void
rte_spinlock_lock(rte_spinlock_t *sl)
{
- while (__sync_lock_test_and_set(&sl->locked, 1))
- while(sl->locked)
+ int exp = 0;
+
+ while (!__atomic_compare_exchange_n(&sl->locked, &exp, 1, 0,
+ __ATOMIC_ACQUIRE, __ATOMIC_RELAXED)) {
+ while (__atomic_load_n(&sl->locked, __ATOMIC_RELAXED))
rte_pause();
+ exp = 0;
+ }
}
#endif
@@ -80,7 +85,7 @@ rte_spinlock_unlock (rte_spinlock_t *sl);
static inline void
rte_spinlock_unlock (rte_spinlock_t *sl)
{
- __sync_lock_release(&sl->locked);
+ __atomic_store_n(&sl->locked, 0, __ATOMIC_RELEASE);
}
#endif
@@ -99,7 +104,10 @@ rte_spinlock_trylock (rte_spinlock_t *sl);
static inline int
rte_spinlock_trylock (rte_spinlock_t *sl)
{
- return __sync_lock_test_and_set(&sl->locked,1) == 0;
+ int exp = 0;
+ return __atomic_compare_exchange_n(&sl->locked, &exp, 1,
+ 0, /* disallow spurious failure */
+ __ATOMIC_ACQUIRE, __ATOMIC_RELAXED);
}
#endif
@@ -113,7 +121,7 @@ rte_spinlock_trylock (rte_spinlock_t *sl)
*/
static inline int rte_spinlock_is_locked (rte_spinlock_t *sl)
{
- return sl->locked;
+ return __atomic_load_n(&sl->locked, __ATOMIC_ACQUIRE);
}
/**