[Question] [k8s] [Performanjce ]Force Tier1 compilation on start

[yahorsi]

Hi Guys,

We run a highly loaded app in Kubernetes and we see perf issues after releasing new versions, partially caused by the JIT compilation, we do have probes but it does not help.

Question: How can we force full app tier1 compilation on the startup? Startup duration is not a big deal as we have liveness probes and k8 will use prev version pods while new starts.

[stephentoub]

You can disable tiered compilation such that everything will initially be compiled with full optimization:
https://learn.microsoft.com/en-us/dotnet/core/runtime-config/compilation#tiered-compilation

Just keep in mind that tiering isn't just about startup. By disabling tiering, you'll also be disabling throughput optimizations that depend on tiering, like dynamic PGO.

You could also explore getting the best of both worlds, using Ready To Run to precompile much of your app but allowing tiering / dynamic PGO to further optimize.

[yahorsi]

Thank you for the reply, disabling tiering won't make the whole app to JIT, my idea was that while the app in k8 starts it still. does not get any requests, so, we have time to fully JIT compile it and use the most optimized tier1, it's not a mobile app where startup time is critical, it's a k8 app that has a liveness probe, so we have time to make all possible optimizations to guarantee that when app responds to the liveness probe - it is fully ready and no any other warmup is needed.

[AndyAyersMS]

We run a highly loaded app in Kubernetes and we see perf issues after releasing new versions, partially caused by the JIT compilation, we do have probes but it does not help.

I think we need to understand better what it is you're seeing. Can you share more details?

Thank you for the reply, disabling tiering won't make the whole app to JIT, my idea was that while the app in k8 starts it still. does not get any requests, so, we have time to fully JIT compile it and use the most optimized tier1,
 
PGO needs to observe the current instance of the app doing its normal processing. There is no way to short-circuit this. The initial observation period is what gives PGO the ability to focus its optimizations.