[dpdk-dev] [PATCH v2 5/6] service: optimize with c11 atomics

[Phil Yang <phil.yang@arm.com>]

The num_mapped_cores is used as a statistics. Use c11 atomics with
RELAXED ordering for num_mapped_cores instead of rte_atomic ops which
enforce unnessary barriers on aarch64.

Replace execute_lock operations to spinlock_try_lock to avoid duplicate
code.

Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
---
 lib/librte_eal/common/rte_service.c | 32 ++++++++++++++++++--------------
 lib/librte_eal/meson.build          |  4 ++++
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 9c1a1d5..8cac265 100644
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -20,6 +20,7 @@
 #include <rte_atomic.h>
 #include <rte_memory.h>
 #include <rte_malloc.h>
+#include <rte_spinlock.h>
 
 #include "eal_private.h"
 
@@ -38,11 +39,11 @@ struct rte_service_spec_impl {
 	/* public part of the struct */
 	struct rte_service_spec spec;
 
-	/* atomic lock that when set indicates a service core is currently
+	/* spin lock that when set indicates a service core is currently
 	 * running this service callback. When not set, a core may take the
 	 * lock and then run the service callback.
 	 */
-	rte_atomic32_t execute_lock;
+	rte_spinlock_t execute_lock;
 
 	/* API set/get-able variables */
 	int8_t app_runstate;
@@ -54,7 +55,7 @@ struct rte_service_spec_impl {
 	 * It does not indicate the number of cores the service is running
 	 * on currently.
 	 */
-	rte_atomic32_t num_mapped_cores;
+	uint32_t num_mapped_cores;
 	uint64_t calls;
 	uint64_t cycles_spent;
 } __rte_cache_aligned;
@@ -332,7 +333,8 @@ rte_service_runstate_get(uint32_t id)
 	rte_smp_rmb();
 
 	int check_disabled = !(s->internal_flags & SERVICE_F_START_CHECK);
-	int lcore_mapped = (rte_atomic32_read(&s->num_mapped_cores) > 0);
+	int lcore_mapped = (__atomic_load_n(&s->num_mapped_cores,
+					    __ATOMIC_RELAXED) > 0);
 
 	return (s->app_runstate == RUNSTATE_RUNNING) &&
 		(s->comp_runstate == RUNSTATE_RUNNING) &&
@@ -375,11 +377,11 @@ service_run(uint32_t i, struct core_state *cs, uint64_t service_mask,
 	cs->service_active_on_lcore[i] = 1;
 
 	if ((service_mt_safe(s) == 0) && (serialize_mt_unsafe == 1)) {
-		if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1))
+		if (!rte_spinlock_trylock(&s->execute_lock))
 			return -EBUSY;
 
 		service_runner_do_callback(s, cs, i);
-		rte_atomic32_clear(&s->execute_lock);
+		rte_spinlock_unlock(&s->execute_lock);
 	} else
 		service_runner_do_callback(s, cs, i);
 
@@ -415,11 +417,11 @@ rte_service_run_iter_on_app_lcore(uint32_t id, uint32_t serialize_mt_unsafe)
 	/* Increment num_mapped_cores to indicate that the service
 	 * is running on a core.
 	 */
-	rte_atomic32_inc(&s->num_mapped_cores);
+	__atomic_add_fetch(&s->num_mapped_cores, 1, __ATOMIC_RELAXED);
 
 	int ret = service_run(id, cs, UINT64_MAX, s, serialize_mt_unsafe);
 
-	rte_atomic32_dec(&s->num_mapped_cores);
+	__atomic_sub_fetch(&s->num_mapped_cores, 1, __ATOMIC_RELAXED);
 
 	return ret;
 }
@@ -556,19 +558,19 @@ service_update(uint32_t sid, uint32_t lcore,
 
 		if (*set && !lcore_mapped) {
 			lcore_states[lcore].service_mask |= sid_mask;
-			rte_atomic32_inc(&rte_services[sid].num_mapped_cores);
+			__atomic_add_fetch(&rte_services[sid].num_mapped_cores,
+					    1, __ATOMIC_RELAXED);
 		}
 		if (!*set && lcore_mapped) {
 			lcore_states[lcore].service_mask &= ~(sid_mask);
-			rte_atomic32_dec(&rte_services[sid].num_mapped_cores);
+			__atomic_sub_fetch(&rte_services[sid].num_mapped_cores,
+					    1, __ATOMIC_RELAXED);
 		}
 	}
 
 	if (enabled)
 		*enabled = !!(lcore_states[lcore].service_mask & (sid_mask));
 
-	rte_smp_wmb();
-
 	return 0;
 }
 
@@ -616,7 +618,8 @@ rte_service_lcore_reset_all(void)
 		}
 	}
 	for (i = 0; i < RTE_SERVICE_NUM_MAX; i++)
-		rte_atomic32_set(&rte_services[i].num_mapped_cores, 0);
+		__atomic_store_n(&rte_services[i].num_mapped_cores, 0,
+				    __ATOMIC_RELAXED);
 
 	rte_smp_wmb();
 
@@ -699,7 +702,8 @@ rte_service_lcore_stop(uint32_t lcore)
 		int32_t enabled = service_mask & (UINT64_C(1) << i);
 		int32_t service_running = rte_service_runstate_get(i);
 		int32_t only_core = (1 ==
-			rte_atomic32_read(&rte_services[i].num_mapped_cores));
+			__atomic_load_n(&rte_services[i].num_mapped_cores,
+					__ATOMIC_RELAXED));
 
 		/* if the core is mapped, and the service is running, and this
 		 * is the only core that is mapped, the service would cease to
diff --git a/lib/librte_eal/meson.build b/lib/librte_eal/meson.build
index 0267c3b..c2d7a69 100644
--- a/lib/librte_eal/meson.build
+++ b/lib/librte_eal/meson.build
@@ -21,3 +21,7 @@ endif
 if cc.has_header('getopt.h')
 	cflags += ['-DHAVE_GETOPT_H', '-DHAVE_GETOPT', '-DHAVE_GETOPT_LONG']
 endif
+# for clang 32-bit compiles we need libatomic for 64-bit atomic ops
+if cc.get_id() == 'clang' and dpdk_conf.get('RTE_ARCH_64') == false
+    ext_deps += cc.find_library('atomic')
+endif
-- 
2.7.4