performance-metrics: Add util module with shared micro benchmark helpers

These factor out common setup and synchronization patterns used by block
layer micro benchmarks.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

Cargo.lock

@@ -1602,6 +1602,7 @@ dependencies = [
  "serde_json",
  "test_infra",
  "thiserror 2.0.18",
+ "vmm-sys-util",
 ]
 
 [[package]]

performance-metrics/Cargo.toml

@@ -11,6 +11,7 @@ serde = { workspace = true, features = ["derive", "rc"] }
 serde_json = { workspace = true }
 test_infra = { path = "../test_infra" }
 thiserror = { workspace = true }
+vmm-sys-util = { workspace = true }
 
 [lints]
 workspace = true

performance-metrics/src/main.rs

@@ -5,6 +5,7 @@
 
 // Custom harness to run performance tests
 mod performance_tests;
+mod util;
 
 use std::process::Command;
 use std::sync::Arc;

performance-metrics/src/util.rs

@@ -0,0 +1,36 @@
+// Copyright 2026 The Cloud Hypervisor Authors. All rights reserved.
+//
+// SPDX-License-Identifier: Apache-2.0
+
+//! Shared benchmark helpers.
+
+use std::io::ErrorKind;
+use std::thread;
+use std::time::Duration;
+
+use vmm_sys_util::eventfd::EventFd;
+use vmm_sys_util::tempfile::TempFile;
+
+pub const BLOCK_SIZE: u64 = 4096;
+
+/// Create a temporary file pre sized to hold `num_blocks` blocks.
+pub fn sized_tempfile(num_blocks: usize) -> TempFile {
+    let tmp = TempFile::new().expect("failed to create tempfile");
+    tmp.as_file()
+        .set_len(BLOCK_SIZE * num_blocks as u64)
+        .expect("failed to set file length");
+    tmp
+}
+
+/// Spin and wait until the given eventfd becomes readable.
+pub fn wait_for_eventfd(notifier: &EventFd) {
+    loop {
+        match notifier.read() {
+            Ok(_) => return,
+            Err(e) if e.kind() == ErrorKind::WouldBlock => {
+                thread::sleep(Duration::from_micros(50));
+            }
+            Err(e) => panic!("eventfd read failed: {e}"),
+        }
+    }
+}