From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 2 Sep 2022 20:19:06 +0000 (-0400)
Subject: __lttng_counter_add: skip effect-less code when global_sum_step=0
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=bf59e80cf46469333f2b7ad74f294640742baaf5;p=lttng-modules.git

__lttng_counter_add: skip effect-less code when global_sum_step=0

Skip effect-less code in the common case where global_sum_step=0.
This saves about 1.5ns on x86-64.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I62e8d163143780e64d7130051b1013470fef48fe
---

diff --git a/include/counter/counter-api.h b/include/counter/counter-api.h
index be372f45..ffc5ff7d 100644
--- a/include/counter/counter-api.h
+++ b/include/counter/counter-api.h
@@ -63,11 +63,13 @@ static __always_inline int __lttng_counter_add(const struct lib_counter_config *
 				move_sum = 0;
 				old = res;
 				n = (int8_t) ((uint8_t) old + (uint8_t) v);
-				if (unlikely(n > (int8_t) global_sum_step))
-					move_sum = (int8_t) global_sum_step / 2;
-				else if (unlikely(n < -(int8_t) global_sum_step))
-					move_sum = -((int8_t) global_sum_step / 2);
-				n -= move_sum;
+				if (unlikely(global_sum_step)) {
+					if (unlikely(n > (int8_t) global_sum_step))
+						move_sum = (int8_t) global_sum_step / 2;
+					else if (unlikely(n < -(int8_t) global_sum_step))
+						move_sum = -((int8_t) global_sum_step / 2);
+					n -= move_sum;
+				}
 				res = cmpxchg_local(int_p, old, n);
 			} while (old != res);
 			break;
@@ -104,11 +106,13 @@ static __always_inline int __lttng_counter_add(const struct lib_counter_config *
 				move_sum = 0;
 				old = res;
 				n = (int16_t) ((uint16_t) old + (uint16_t) v);
-				if (unlikely(n > (int16_t) global_sum_step))
-					move_sum = (int16_t) global_sum_step / 2;
-				else if (unlikely(n < -(int16_t) global_sum_step))
-					move_sum = -((int16_t) global_sum_step / 2);
-				n -= move_sum;
+				if (unlikely(global_sum_step)) {
+					if (unlikely(n > (int16_t) global_sum_step))
+						move_sum = (int16_t) global_sum_step / 2;
+					else if (unlikely(n < -(int16_t) global_sum_step))
+						move_sum = -((int16_t) global_sum_step / 2);
+					n -= move_sum;
+				}
 				res = cmpxchg_local(int_p, old, n);
 			} while (old != res);
 			break;
@@ -145,11 +149,13 @@ static __always_inline int __lttng_counter_add(const struct lib_counter_config *
 				move_sum = 0;
 				old = res;
 				n = (int32_t) ((uint32_t) old + (uint32_t) v);
-				if (unlikely(n > (int32_t) global_sum_step))
-					move_sum = (int32_t) global_sum_step / 2;
-				else if (unlikely(n < -(int32_t) global_sum_step))
-					move_sum = -((int32_t) global_sum_step / 2);
-				n -= move_sum;
+				if (unlikely(global_sum_step)) {
+					if (unlikely(n > (int32_t) global_sum_step))
+						move_sum = (int32_t) global_sum_step / 2;
+					else if (unlikely(n < -(int32_t) global_sum_step))
+						move_sum = -((int32_t) global_sum_step / 2);
+					n -= move_sum;
+				}
 				res = cmpxchg_local(int_p, old, n);
 			} while (old != res);
 			break;
@@ -187,11 +193,13 @@ static __always_inline int __lttng_counter_add(const struct lib_counter_config *
 				move_sum = 0;
 				old = res;
 				n = (int64_t) ((uint64_t) old + (uint64_t) v);
-				if (unlikely(n > (int64_t) global_sum_step))
-					move_sum = (int64_t) global_sum_step / 2;
-				else if (unlikely(n < -(int64_t) global_sum_step))
-					move_sum = -((int64_t) global_sum_step / 2);
-				n -= move_sum;
+				if (unlikely(global_sum_step)) {
+					if (unlikely(n > (int64_t) global_sum_step))
+						move_sum = (int64_t) global_sum_step / 2;
+					else if (unlikely(n < -(int64_t) global_sum_step))
+						move_sum = -((int64_t) global_sum_step / 2);
+					n -= move_sum;
+				}
 				res = cmpxchg_local(int_p, old, n);
 			} while (old != res);
 			break;