Async vs Await Benchmark (.NET)

This benchmark compares the performance impact of using async/await with Task and ValueTask in C#. It focuses on scenarios where the asynchronous operation is trivial and completes immediately, such as returning a constant value.

Purpose

The goal is to understand the overhead introduced by async/await in cases where it may be unnecessary. For example, returning a cached value or a precomputed result in an async method.

Benchmark Cases

Method Name	Description
GetStringSync	Returns a string synchronously.
GetStringWithoutAsync	Returns Task<string> without using async or await.
GetStringWithAsync	Uses async + await, wrapping Task.FromResult.
GetStringWithoutAsyncValue	Returns ValueTask<string> without using async or await.
GetStringWithAsyncValue	Uses async + await, wrapping ValueTask.FromResult.

Key Takeaways

• Avoid unnecessary async/await if the method doesn't actually await anything.
• Using Task.FromResult or ValueTask.FromResult directly is more efficient, as it avoids state machine generation and heap allocations.
• ValueTask<T> can be more efficient than Task<T> for frequently synchronous results.
• In real-world I/O-bound scenarios, this overhead is negligible, but in performance-critical code paths (e.g., high-frequency methods, microservices, low-latency systems), it can add up.

Example

private Task<string> GetStringWithoutAsyncCore()
{
    return Task.FromResult("I'm great developer.");
}

private async Task<string> GetStringWithAsyncCore()
{
    return await Task.FromResult("I'm great developer.");
}

Benchmark

Method	Mean	Error	StdDev	Gen0	Allocated
GetStringWithAsync	30.4626 ns	0.7727 ns	2.2295 ns	0.0344	216 B
GetStringWithoutAsync	17.3824 ns	0.3938 ns	0.6471 ns	0.0229	144 B
GetStringWithoutAsyncValue	10.6441 ns	0.0675 ns	0.0598 ns	-	-
GetStringWithAsyncValue	17.6272 ns	0.1637 ns	0.1278 ns	-	-
GetStringSync	0.0625 ns	0.0202 ns	0.0189 ns	-	-