2x RPS improvement in Json-https benchmark. why?

[EgorBo]

It'd be nice to identify why we're seeing a stable 2x RPS (very uncommon to see) improvement in this benchmark (https://aka.ms/aspnet/benchmarks, 2nd page) but only on AMD machine 😮

commit range in dotnet/runtime: a78211b...4adb117
commit range in dotnet/aspnetcore: dotnet/aspnetcore@ab3e5e2...10b1fd9

cc @sebastienros

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[EgorBo]

I wonder if it could be dotnet/aspnetcore#41790 (slow vpblendvb?) cc @meziantou

[EgorBo]

ah, looks like dotnet/aspnetcore#42237 so dotnet/runtime is probably the wrong repo for it
cc @halter73

[sebastienros]

Yes, this should be it, since this is removing the bottlenecks on high cores. Visible on AMD because it's the machine with the most used cores. So far we capped the Ampere machines to 28 cores for this reason. I will configure a different ARM profile using 80 cores. We'll see the differences compared to 6.0 in the KPIs.