perf: Small perf optimization for logs (open-telemetry#2799)

Author: cijothomas

CHANGELOG.md

@@ -47,6 +47,8 @@ when conversion is feasible. Otherwise stored as
 `opentelemetry::logs::AnyValue::String`. This avoids unnecessary string
 allocation when values can be represented in their original types.
 
+- perf - small perf improvement by avoiding string allocation of `target`
+
 ## 0.28.1
 
 Released 2025-Feb-12

benches/logs.rs

@@ -10,7 +10,7 @@
     | noop_layer_disabled         | 12 ns       |
     | noop_layer_enabled          | 25 ns       |
     | ot_layer_disabled           | 19 ns       |
-    | ot_layer_enabled            | 167 ns      |
+    | ot_layer_enabled            | 155 ns      |
 
     Hardware: Apple M4 Pro
     Total Number of Cores:	14 (10 performance and 4 efficiency)
@@ -20,7 +20,7 @@
     | noop_layer_disabled         | 8 ns       |
     | noop_layer_enabled          | 14 ns       |
     | ot_layer_disabled           | 12 ns       |
-    | ot_layer_enabled            | 186 ns      |
+    | ot_layer_enabled            | 130 ns      |
 */
 
 use criterion::{criterion_group, criterion_main, Criterion};

src/layer.rs

@@ -189,8 +189,7 @@ where
 
         let mut log_record = self.logger.create_log_record();
 
-        // TODO: Fix heap allocation
-        log_record.set_target(target.to_string());
+        log_record.set_target(target);
         log_record.set_event_name(name);
         log_record.set_severity_number(severity);
         log_record.set_severity_text(metadata.level().as_str());