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authorjaszha03 <jason.zhang2@arm.com>2019-07-01 17:08:57 -0500
committerFlorin Coras <florin.coras@gmail.com>2019-08-01 18:01:33 +0000
commit30aaf97a90230d68c0f2736b0a026e07b06e7e32 (patch)
treefcfa22ff97deab6c60be759f183b2fcab92c6210
parent691a3b7f11c41851d747e35c6bc5db9319d92c20 (diff)
vppinfra: refactor clib_rwlock_t to use single condition variable
Previous implementation of clib_rwlock_t used two spinlocks: one writer lock, and one to guard the counter for the number of readers. This implementation uses a single condition variable rw_cnt which has the following properties: if a writer has the rwlock, rw_cnt = -1 if the rwlock is free, rw_cnt = 0 otherwise, rw_cnt > 0 and rw_cnt = number of readers rw_cnt will never be less than -1 Benchmarking: The results below are the cycle counts from test_rwlock.c, configured so that for 10000 iterations, 6 reader and 6 writer threads on separate cores are spawned such that each writer thread increments a global counter 10000 times in each iteration. For Taishan, 4 reader and 4 writer threads are spawned in each test. x86 Xeon old rwlock: 12.473e8, 11.655e8, 13.201e8, 11.347e8, 13.182e8 x86 Xeon new rwlock: 5.881e8, 5.796e8, 6.536e8, 5.540e8, 5.890e8 Aarch64 ThX2* old rwlock: 9.263e7, 8.933e7, 9.074e7, 8.979e7, 9.378e7 Aarch64 ThX2* new rwlock: 7.221e7, 8.107e7, 7.515e7, 7.672e7, 7.386e7 A72 old rwlock: 3.268e6, 3.200e6, 3.086e6, 3.176e6, 3.170e6 A72 new rwlock: 1.261e6, 1.288e6, 1.251e6, 1.229e6, 1.234e6 *ThunderX2 used additional gcc options "-march=armv8.1-a+crc+crypto+lse" Type: refactor Change-Id: I7c347d3037b36205ab532cbcb52a374c846eb275 Signed-off-by: Jason Zhang <jason.zhang2@arm.com> Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com> Reviewed-by: Lijian Zhang <Lijian.Zhang@arm.com>
-rw-r--r--src/vnet/session/segment_manager.c1
-rw-r--r--src/vppinfra/lock.h43
2 files changed, 19 insertions, 25 deletions
diff --git a/src/vnet/session/segment_manager.c b/src/vnet/session/segment_manager.c
index c0785695d4f..9c33e35e8f0 100644
--- a/src/vnet/session/segment_manager.c
+++ b/src/vnet/session/segment_manager.c
@@ -280,7 +280,6 @@ segment_manager_get_segment_w_lock (segment_manager_t * sm, u32 segment_index)
void
segment_manager_segment_reader_unlock (segment_manager_t * sm)
{
- ASSERT (sm->segments_rwlock->n_readers > 0);
clib_rwlock_reader_unlock (&sm->segments_rwlock);
}
diff --git a/src/vppinfra/lock.h b/src/vppinfra/lock.h
index c1f0b87dfc6..49e849b1bdd 100644
--- a/src/vppinfra/lock.h
+++ b/src/vppinfra/lock.h
@@ -118,9 +118,8 @@ clib_spinlock_unlock_if_init (clib_spinlock_t * p)
typedef struct clib_rw_lock_
{
CLIB_CACHE_LINE_ALIGN_MARK (cacheline0);
- volatile u32 n_readers;
- volatile u32 n_readers_lock;
- volatile u32 writer_lock;
+ /* -1 when W lock held, > 0 when R lock held */
+ volatile i32 rw_cnt;
#if CLIB_DEBUG > 0
pid_t pid;
uword thread_index;
@@ -148,41 +147,37 @@ clib_rwlock_free (clib_rwlock_t * p)
always_inline void
clib_rwlock_reader_lock (clib_rwlock_t * p)
{
- while (clib_atomic_test_and_set (&(*p)->n_readers_lock))
- CLIB_PAUSE ();
-
- (*p)->n_readers += 1;
- if ((*p)->n_readers == 1)
+ i32 cnt;
+ do
{
- while (clib_atomic_test_and_set (&(*p)->writer_lock))
+ /* rwlock held by a writer */
+ while ((cnt = clib_atomic_load_relax_n (&(*p)->rw_cnt)) < 0)
CLIB_PAUSE ();
}
- clib_atomic_release (&(*p)->n_readers_lock);
+ while (!clib_atomic_cmp_and_swap_acq_relax_n
+ (&(*p)->rw_cnt, &cnt, cnt + 1, 1));
CLIB_LOCK_DBG (p);
}
always_inline void
clib_rwlock_reader_unlock (clib_rwlock_t * p)
{
- ASSERT ((*p)->n_readers > 0);
+ ASSERT ((*p)->rw_cnt > 0);
CLIB_LOCK_DBG_CLEAR (p);
-
- while (clib_atomic_test_and_set (&(*p)->n_readers_lock))
- CLIB_PAUSE ();
-
- (*p)->n_readers -= 1;
- if ((*p)->n_readers == 0)
- {
- clib_atomic_release (&(*p)->writer_lock);
- }
- clib_atomic_release (&(*p)->n_readers_lock);
+ clib_atomic_fetch_sub_rel (&(*p)->rw_cnt, 1);
}
always_inline void
clib_rwlock_writer_lock (clib_rwlock_t * p)
{
- while (clib_atomic_test_and_set (&(*p)->writer_lock))
- CLIB_PAUSE ();
+ i32 cnt = 0;
+ do
+ {
+ /* rwlock held by writer or reader(s) */
+ while ((cnt = clib_atomic_load_relax_n (&(*p)->rw_cnt)) != 0)
+ CLIB_PAUSE ();
+ }
+ while (!clib_atomic_cmp_and_swap_acq_relax_n (&(*p)->rw_cnt, &cnt, -1, 1));
CLIB_LOCK_DBG (p);
}
@@ -190,7 +185,7 @@ always_inline void
clib_rwlock_writer_unlock (clib_rwlock_t * p)
{
CLIB_LOCK_DBG_CLEAR (p);
- clib_atomic_release (&(*p)->writer_lock);
+ clib_atomic_release (&(*p)->rw_cnt);
}
#endif