benchmarking: fix DB read/write counts

prdoc/pr_10947.prdoc

@@ -0,0 +1,9 @@
+title: 'benchmarking: fix DB read/write counts'
+doc:
+- audience: Runtime Dev
+  description: |-
+    PR #10802 added `reset_read_write_count()` at the end of commit_db() to prevent warmup operations from appearing in benchmarking results. However, commit_db is called twice: one on `on_before_start()` closure before benchmark, and one after benchmark execution after benchmark.
+    This PR whitelists warmup key so that it doesn't appear in the read/write count.
+crates:
+- name: frame-benchmarking
+  bump: patch

substrate/frame/benchmarking/src/utils.rs

@@ -293,13 +293,16 @@ pub trait Benchmarking {
 
 		// Warmup the memory allocator after bulk deallocation.
 		// After draining the overlay with many entries, the first new allocation can trigger memory
-		// defragmentation.
+		// defragmentation. The warmup key is whitelisted so these operations don't appear in
+		// benchmark results.
 		const WARMUP_KEY: &[u8] = b":benchmark_warmup:";
+		let mut whitelist = self.get_whitelist();
+		if !whitelist.iter().any(|k| k.key == WARMUP_KEY) {
+			whitelist.push(WARMUP_KEY.to_vec().into());
+			self.set_whitelist(whitelist);
+		}
 		self.place_storage(WARMUP_KEY.to_vec(), Some(vec![0u8; 32]));
 		self.place_storage(WARMUP_KEY.to_vec(), None);
-
-		// Reset tracking so warmup operations don't appear in benchmark results.
-		self.reset_read_write_count();
 	}
 
 	/// Get the read/write count.