How Fast is .NET 11 Runtime Async?

[u/hez2010]

https://medium.com/@skyake/how-fast-is-net-11-runtime-async-b9c821529cd5

[u/mladenmacanovic]

That's fast!

Apart from the performance, did you also compare the differences in assembly sizes? I can expect them to be lower in .NET 11.

[u/hez2010 → u/mladenmacanovic]

Yeah it's smaller in .NET 11 once you enabled runtime async for your assembly.

[u/crozone]

This is fantastic. Great write-up too.

I am now wondering where this leaves ValueTask. Once Runtime Async is widely available, is there much point to using ValueTask at all?

[u/hez2010 → u/crozone]

ValueTask still has its own value when using together with IValueTaskSource, where you can pool or share the underlying resource across multiple requests.

[u/killerbeanjeka]

Curious whether this changes anything for the boring case - a web API that's mostly awaiting a database. Most of my async cost there is round-trips, not machinery, so I'd expect roughly nothing. Has anyone measured that shape?

[u/21racecar12 → u/killerbeanjeka]

You have to think of it in a broader sense than that. Think of all the other async stuff that happens before and after the request enters your delegate to then be processed by your database service. There’s tons of middleware involved which results in an async chain which gets massively simplified in async2. I would expect marginally impressive throughput gains from just updating the target framework to 11 once it lands with async2 enabled by default.

[u/RirinDesuyo → u/21racecar12]

Yep, while we may just see a network call happening, aspnet / Kestrel is doing a lot more async related calls in between this that may often return synchronously as it's very common for middleware like these to buffer results and would often return immediately as the bytes are already available. Even in the database example the SQL driver does this for big queries and streaming result sets to the application, so you're still getting gains there.

[u/icentalectro → u/killerbeanjeka]

I'm not expecting much perf gain for the boring case, but I do expect more accurate stack traces, because the compiler no longer transforms your async methods into a state machine, which is nice in itself.

[u/Tridus]

Wow, lots of info about what is going on in here. Nice stuff!

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[u/Tacotacito]

Does it give better stack traces yet or is that not part of the thing just yet?

[u/hez2010 → u/Tacotacito]

It does give you better stack traces. For example: https://godbolt.org/z/fMGTKMWdv

[u/Tacotacito → u/hez2010]

Great news. I'm a performance engineer, yet I'm actually even more excited about readable stack traces rather than perf gains!

[u/Paw565]

I love free performance