[Xamarin.Android] Performance regression between net7 and net8

[grendello]

We've observed that a plain "hello world" Xamarin.Android application (dotnet new android) starts up slower
than it did under net7. The slowdown cannot be attribute to changes in XA itself, as there haven't been any
changes that could affect performance to this degree. Our performance test measures three startup metrics:

• "Application displayed time" as reported by the Android OS. This is measured by the system and is the
  time between starting the application (via intent or by clicking its icon in the UI) and the point where
  the application frame is fully painted. This metric regressed by an average of 11% across 10 test runs.
• First managed call performance (we call a static class method which does some initialization for us).
  This metric regressed by around 50%
• The "total init time" is the time spent in the native XA runtime. This includes the "first managed call"
  sequence above, plus MonoVM initialization, loading of some assemblies as needed to make the first managed
  call, setting up handlers etc. This metric regressed by about 25%

XA uses profiled AOT to improve startup time, and recording a new profile allowed me to see what new methods
are called at startup. Here's a set of them that has the biggest potential to adversely affect performance:

+       bool System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:MoveNext ()
+       bool System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:MoveNextRare ()
+       bool System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:Contains (System.Diagnostics.Metrics.Instrument)
+       bool System.Diagnostics.Metrics.Meter:AddInstrument (System.Diagnostics.Metrics.Instrument)
+       bool System.Globalization.CultureData:IsValidCultureName (string,int&,int&)
+       bool System.Guid:TryWriteBytes (System.Span`1<byte>)
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1/ConfiguredTaskAwaiter<Java.Net.Proxy>:get_IsCompleted ()
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1/ConfiguredTaskAwaiter<System.Net.HttpStatusCode>:get_IsCompleted ()
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable/ConfiguredTaskAwaiter:get_IsCompleted ()
+       bool System.RuntimeTypeHandle:IsFunctionPointer (System.RuntimeType)
+       Interop/Globalization/ResultCode System.TimeZoneInfo/<>c:<GetDisplayName>b__192_0 (System.Span`1<char>,string,string,Interop/Globalization/TimeZoneDisplayNameType)
+       Interop/Sys/OpenFlags Microsoft.Win32.SafeHandles.SafeFileHandle:PreOpenConfigurationFromOptions (System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,System.IO.FileOptions,bool)
+       int System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:IndexOf (System.Diagnostics.Metrics.Instrument)
+       object System.Diagnostics.Metrics.Instrument:get_SyncObject ()
+       object System.Reflection.MethodBaseInvoker:InterpretedInvoke_Constructor (object,intptr*)
+       object System.Reflection.MethodBaseInvoker:InterpretedInvoke_Method (object,intptr*)
+       object System.Reflection.MethodBaseInvoker:InvokeConstructorWithoutAlloc (object,bool)
+       object System.Reflection.MethodBaseInvoker:InvokeDirectByRefWithFewArgs (object,System.Span`1<object>,System.Reflection.BindingFlags)
+       object System.Reflection.MethodBaseInvoker:InvokeWithFewArgs (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo)
+       object System.Reflection.MethodBaseInvoker:InvokeWithNoArgs (object,System.Reflection.BindingFlags)
+       string System.Globalization.CultureData:NormalizeCultureName (string,System.ReadOnlySpan`1<char>,int&)
+       string System.TimeZoneInfo:get_DaylightName ()
+       string System.TimeZoneInfo:get_DisplayName ()
+       string System.TimeZoneInfo:PopulateDaylightDisplayName ()
+       string System.TimeZoneInfo:PopulateDisplayName ()
+       string System.TimeZoneInfo:PopulateStandardDisplayName ()
+       System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument> System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:GetEnumerator ()
+       System.Collections.Generic.List`1<System.Diagnostics.Metrics.MeterListener> System.Diagnostics.Metrics.MeterListener:GetAllListeners ()
+       System.Diagnostics.Metrics.Counter`1<long> System.Diagnostics.Metrics.Meter:CreateCounter (string,string,string)
+       System.Diagnostics.Metrics.Counter`1<long> System.Diagnostics.Metrics.Meter:CreateCounter (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Histogram`1<double> System.Diagnostics.Metrics.Meter:CreateHistogram (string,string,string)
+       System.Diagnostics.Metrics.Histogram`1<double> System.Diagnostics.Metrics.Meter:CreateHistogram (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass29_0`1<System.Int64>:<CreateCounter>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass31_0`1<System.Double>:<CreateHistogram>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass33_0`1<System.Int64>:<CreateUpDownCounter>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetCachedInstrument (System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>,System.Type,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetOrCreateInstrument (System.Type,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,System.Func`1<System.Diagnostics.Metrics.Instrument>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetOrCreateInstrument (System.Type,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,System.Func`1<System.Diagnostics.Metrics.Instrument>)
+       System.Diagnostics.Metrics.Meter System.Net.Http.Metrics.MetricsHandler/SharedMeter:get_Instance ()
+       System.Diagnostics.Metrics.UpDownCounter`1<long> System.Diagnostics.Metrics.Meter:CreateUpDownCounter (string,string,string)
+       System.Diagnostics.Metrics.UpDownCounter`1<long> System.Diagnostics.Metrics.Meter:CreateUpDownCounter (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Guid System.Reflection.RuntimeModule:get_ModuleVersionId ()
+       System.Guid System.Reflection.RuntimeModule:GetModuleVersionId ()
+       System.Net.Http.Metrics.MetricsHandler System.Net.Http.HttpClientHandler:SetupHandlerChain ()
+       System.Reflection.MethodInfo System.Type:GetMethod (string,System.Reflection.BindingFlags,System.Reflection.Binder,System.Reflection.CallingConventions,System.Type[],System.Reflection.ParameterModifier[])
+       System.Reflection.MethodInfo System.Type:GetMethod (string,System.Reflection.BindingFlags,System.Reflection.Binder,System.Type[],System.Reflection.ParameterModifier[])
+       System.Reflection.Module System.RuntimeType:get_Module ()
+       System.Threading.Tasks.Task`1<System.Net.Http.HttpResponseMessage> System.Net.Http.HttpMessageHandlerStage:SendAsync (System.Net.Http.HttpRequestMessage,System.Threading.CancellationToken)
+       System.Threading.Tasks.Task`1<System.Net.Http.HttpResponseMessage> System.Threading.Tasks.ValueTask`1<System.Net.Http.HttpResponseMessage>:AsTask ()
+       System.Threading.Tasks.ValueTask`1<System.Net.Http.HttpResponseMessage> System.Net.Http.Metrics.MetricsHandler:SendAsync (System.Net.Http.HttpRequestMessage,bool,System.Threading.CancellationToken)
+       System.TimeZoneInfo/AdjustmentRule[] System.Collections.Generic.List`1<System.TimeZoneInfo/AdjustmentRule>:ToArray ()
+       void System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:.ctor (System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>)
+       void System.Diagnostics.Metrics.Counter`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Histogram`1<System.Double>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument`1<System.Double>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument/<>c:.cctor ()
+       void System.Diagnostics.Metrics.Instrument/<>c:.ctor ()
+       void System.Diagnostics.Metrics.Instrument:.cctor ()
+       void System.Diagnostics.Metrics.Instrument:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument:Publish ()
+       void System.Diagnostics.Metrics.Instrument:ValidateTypeParameter ()
+       void System.Diagnostics.Metrics.Instrument:ValidateTypeParameter ()
+       void System.Diagnostics.Metrics.Meter/<>c:.cctor ()
+       void System.Diagnostics.Metrics.Meter/<>c:.ctor ()
+       void System.Diagnostics.Metrics.Meter:.cctor ()
+       void System.Diagnostics.Metrics.Meter:.ctor (string)
+       void System.Diagnostics.Metrics.Meter:.ctor (string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,object)
+       void System.Diagnostics.Metrics.Meter:Initialize (string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,object)
+       void System.Diagnostics.Metrics.MeterListener:.cctor ()
+       void System.Diagnostics.Metrics.MetricsEventSource:.cctor ()
+       void System.Diagnostics.Metrics.MetricsEventSource:.ctor ()
+       void System.Diagnostics.Metrics.UpDownCounter`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Net.Http.Metrics.MetricsHandler:.ctor (System.Net.Http.HttpMessageHandler,System.Diagnostics.Metrics.IMeterFactory,System.Diagnostics.Metrics.Meter&)
+       void System.Net.Http.Metrics.MetricsHandler/SharedMeter:.cctor ()
+       void System.Net.Http.Metrics.MetricsHandler/SharedMeter:.ctor ()
+       void System.TimeZoneInfo:GetDaylightDisplayName (string,string&)
+       void System.TimeZoneInfo:GetFullValueForDisplayNameField (string,System.TimeSpan,string&)
+       void System.TimeZoneInfo:GetStandardDisplayName (string,string&)

The worrying parts are the HTTP requests, the System.Diagnostic.Metrics calls, the TPL use and the timezone data - the latter was greatly improved lately, but it appears that accessing timezone data has somehow become part of the default startup path.
startup (the biggest issue here is retrieving the zone's display name, which is an expensive operation)

Tagging subscribers to 'arch-android': @steveisok, @akoeplinger
See info in area-owners.md if you want to be subscribed.

Issue Details

---

We've observed that a plain "hello world" Xamarin.Android application (dotnet new android) starts up slower
than it did under net7. The slowdown cannot be attribute to changes in XA itself, as there haven't been any
changes that could affect performance to this degree. Our performance test measures three startup metrics:

• "Application displayed time" as reported by the Android OS. This is measured by the system and is the
  time between starting the application (via intent or by clicking its icon in the UI) and the point where
  the application frame is fully painted. This metric regressed by an average of 11% across 10 test runs.
• First managed call performance (we call a static class method which does some initialization for us).
  This metric regressed by around 50%
• The "total init time" is the time spent in the native XA runtime. This includes the "first managed call"
  sequence above, plus MonoVM initialization, loading of some assemblies as needed to make the first managed
  call, setting up handlers etc. This metric regressed by about 25%

XA uses profiled AOT to improve startup time, and recording a new profile allowed me to see what new methods
are called at startup. Here's a set of them that has the biggest potential to adversely affect performance:

+       bool System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:MoveNext ()
+       bool System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:MoveNextRare ()
+       bool System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:Contains (System.Diagnostics.Metrics.Instrument)
+       bool System.Diagnostics.Metrics.Meter:AddInstrument (System.Diagnostics.Metrics.Instrument)
+       bool System.Globalization.CultureData:IsValidCultureName (string,int&,int&)
+       bool System.Guid:TryWriteBytes (System.Span`1<byte>)
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1/ConfiguredTaskAwaiter<Java.Net.Proxy>:get_IsCompleted ()
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1/ConfiguredTaskAwaiter<System.Net.HttpStatusCode>:get_IsCompleted ()
+       bool System.Runtime.CompilerServices.ConfiguredTaskAwaitable/ConfiguredTaskAwaiter:get_IsCompleted ()
+       bool System.RuntimeTypeHandle:IsFunctionPointer (System.RuntimeType)
+       Interop/Globalization/ResultCode System.TimeZoneInfo/<>c:<GetDisplayName>b__192_0 (System.Span`1<char>,string,string,Interop/Globalization/TimeZoneDisplayNameType)
+       Interop/Sys/OpenFlags Microsoft.Win32.SafeHandles.SafeFileHandle:PreOpenConfigurationFromOptions (System.IO.FileMode,System.IO.FileAccess,System.IO.FileShare,System.IO.FileOptions,bool)
+       int System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:IndexOf (System.Diagnostics.Metrics.Instrument)
+       object System.Diagnostics.Metrics.Instrument:get_SyncObject ()
+       object System.Reflection.MethodBaseInvoker:InterpretedInvoke_Constructor (object,intptr*)
+       object System.Reflection.MethodBaseInvoker:InterpretedInvoke_Method (object,intptr*)
+       object System.Reflection.MethodBaseInvoker:InvokeConstructorWithoutAlloc (object,bool)
+       object System.Reflection.MethodBaseInvoker:InvokeDirectByRefWithFewArgs (object,System.Span`1<object>,System.Reflection.BindingFlags)
+       object System.Reflection.MethodBaseInvoker:InvokeWithFewArgs (object,System.Reflection.BindingFlags,System.Reflection.Binder,object[],System.Globalization.CultureInfo)
+       object System.Reflection.MethodBaseInvoker:InvokeWithNoArgs (object,System.Reflection.BindingFlags)
+       string System.Globalization.CultureData:NormalizeCultureName (string,System.ReadOnlySpan`1<char>,int&)
+       string System.TimeZoneInfo:get_DaylightName ()
+       string System.TimeZoneInfo:get_DisplayName ()
+       string System.TimeZoneInfo:PopulateDaylightDisplayName ()
+       string System.TimeZoneInfo:PopulateDisplayName ()
+       string System.TimeZoneInfo:PopulateStandardDisplayName ()
+       System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument> System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>:GetEnumerator ()
+       System.Collections.Generic.List`1<System.Diagnostics.Metrics.MeterListener> System.Diagnostics.Metrics.MeterListener:GetAllListeners ()
+       System.Diagnostics.Metrics.Counter`1<long> System.Diagnostics.Metrics.Meter:CreateCounter (string,string,string)
+       System.Diagnostics.Metrics.Counter`1<long> System.Diagnostics.Metrics.Meter:CreateCounter (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Histogram`1<double> System.Diagnostics.Metrics.Meter:CreateHistogram (string,string,string)
+       System.Diagnostics.Metrics.Histogram`1<double> System.Diagnostics.Metrics.Meter:CreateHistogram (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass29_0`1<System.Int64>:<CreateCounter>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass31_0`1<System.Double>:<CreateHistogram>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter/<>c__DisplayClass33_0`1<System.Int64>:<CreateUpDownCounter>b__0 ()
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetCachedInstrument (System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>,System.Type,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetOrCreateInstrument (System.Type,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,System.Func`1<System.Diagnostics.Metrics.Instrument>)
+       System.Diagnostics.Metrics.Instrument System.Diagnostics.Metrics.Meter:GetOrCreateInstrument (System.Type,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,System.Func`1<System.Diagnostics.Metrics.Instrument>)
+       System.Diagnostics.Metrics.Meter System.Net.Http.Metrics.MetricsHandler/SharedMeter:get_Instance ()
+       System.Diagnostics.Metrics.UpDownCounter`1<long> System.Diagnostics.Metrics.Meter:CreateUpDownCounter (string,string,string)
+       System.Diagnostics.Metrics.UpDownCounter`1<long> System.Diagnostics.Metrics.Meter:CreateUpDownCounter (string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       System.Guid System.Reflection.RuntimeModule:get_ModuleVersionId ()
+       System.Guid System.Reflection.RuntimeModule:GetModuleVersionId ()
+       System.Net.Http.Metrics.MetricsHandler System.Net.Http.HttpClientHandler:SetupHandlerChain ()
+       System.Reflection.MethodInfo System.Type:GetMethod (string,System.Reflection.BindingFlags,System.Reflection.Binder,System.Reflection.CallingConventions,System.Type[],System.Reflection.ParameterModifier[])
+       System.Reflection.MethodInfo System.Type:GetMethod (string,System.Reflection.BindingFlags,System.Reflection.Binder,System.Type[],System.Reflection.ParameterModifier[])
+       System.Reflection.Module System.RuntimeType:get_Module ()
+       System.Threading.Tasks.Task`1<System.Net.Http.HttpResponseMessage> System.Net.Http.HttpMessageHandlerStage:SendAsync (System.Net.Http.HttpRequestMessage,System.Threading.CancellationToken)
+       System.Threading.Tasks.Task`1<System.Net.Http.HttpResponseMessage> System.Threading.Tasks.ValueTask`1<System.Net.Http.HttpResponseMessage>:AsTask ()
+       System.Threading.Tasks.ValueTask`1<System.Net.Http.HttpResponseMessage> System.Net.Http.Metrics.MetricsHandler:SendAsync (System.Net.Http.HttpRequestMessage,bool,System.Threading.CancellationToken)
+       System.TimeZoneInfo/AdjustmentRule[] System.Collections.Generic.List`1<System.TimeZoneInfo/AdjustmentRule>:ToArray ()
+       void System.Collections.Generic.List`1/Enumerator<System.Diagnostics.Metrics.Instrument>:.ctor (System.Collections.Generic.List`1<System.Diagnostics.Metrics.Instrument>)
+       void System.Diagnostics.Metrics.Counter`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Histogram`1<System.Double>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument`1<System.Double>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument/<>c:.cctor ()
+       void System.Diagnostics.Metrics.Instrument/<>c:.ctor ()
+       void System.Diagnostics.Metrics.Instrument:.cctor ()
+       void System.Diagnostics.Metrics.Instrument:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Diagnostics.Metrics.Instrument:Publish ()
+       void System.Diagnostics.Metrics.Instrument:ValidateTypeParameter ()
+       void System.Diagnostics.Metrics.Instrument:ValidateTypeParameter ()
+       void System.Diagnostics.Metrics.Meter/<>c:.cctor ()
+       void System.Diagnostics.Metrics.Meter/<>c:.ctor ()
+       void System.Diagnostics.Metrics.Meter:.cctor ()
+       void System.Diagnostics.Metrics.Meter:.ctor (string)
+       void System.Diagnostics.Metrics.Meter:.ctor (string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,object)
+       void System.Diagnostics.Metrics.Meter:Initialize (string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>,object)
+       void System.Diagnostics.Metrics.MeterListener:.cctor ()
+       void System.Diagnostics.Metrics.MetricsEventSource:.cctor ()
+       void System.Diagnostics.Metrics.MetricsEventSource:.ctor ()
+       void System.Diagnostics.Metrics.UpDownCounter`1<System.Int64>:.ctor (System.Diagnostics.Metrics.Meter,string,string,string,System.Collections.Generic.IEnumerable`1<System.Collections.Generic.KeyValuePair`2<string, object>>)
+       void System.Net.Http.Metrics.MetricsHandler:.ctor (System.Net.Http.HttpMessageHandler,System.Diagnostics.Metrics.IMeterFactory,System.Diagnostics.Metrics.Meter&)
+       void System.Net.Http.Metrics.MetricsHandler/SharedMeter:.cctor ()
+       void System.Net.Http.Metrics.MetricsHandler/SharedMeter:.ctor ()
+       void System.TimeZoneInfo:GetDaylightDisplayName (string,string&)
+       void System.TimeZoneInfo:GetFullValueForDisplayNameField (string,System.TimeSpan,string&)
+       void System.TimeZoneInfo:GetStandardDisplayName (string,string&)

The worrying parts are the HTTP requests, the System.Diagnostic.Metrics calls, the TPL use and the timezone data - the latter was greatly improved lately, but it appears that accessing timezone data has somehow become part of the default startup path.
startup (the biggest issue here is retrieving the zone's display name, which is an expensive operation)

Author:	grendello
Assignees:	-
Labels:	os-android, untriaged, area-System.Diagnostics.Metric
Milestone:	-

[steveisok]

/cc @SamMonoRT

[grendello]

The profile is recorded with this application https://github.com/xamarin/xamarin-android/blob/main/src/profiled-aot/CommonMethods.cs

This explains the TPL and the HTTP, luckily :) The TZ requests and the metrics handler are still worrying.

[SamMonoRT]

cc @vargaz @fanyang-mono

[SamMonoRT]

@mdh1418 @tarekgh - do you think #89985 should help some of the Android startup regressions related to expensive TimeZone requests?

[SamMonoRT]

@antonfirsov - can #87319 cause a startup regression. @grendello is it possible to coordinate with @antonfirsov to run some profiles before/after the change.

[antonfirsov]

/cc @MihaZupan @karelz and also @tarekgh in case this will be root caused to Meter performance.

@grendello since we don't have experience with Android, can you help us by running profiler/benchmarks?

[mdh1418]

@mdh1418 @tarekgh - do you think #89985 should help some of the Android startup regressions related to expensive TimeZone requests?

If GetSystemTimeZones is the only caller to the string System.TimeZoneInfo:get_DisplayName () reported in the new methods being hit in the profile, it would help. However not sure what exactly is invoking that right now

[grendello]

@antonfirsov if you point me to the commits I need to test, I can do the rest :) Note that this is not part of the startup for a hello world app, but the AOT profile recording app linked to above. However, any non-trivial app is likely to hit the same code path, so it would be great if we could address that.

[grendello]

@antonfirsov it would be ideal if metrics were disabled by default, but easily enabled by setting an msbuild property of something. On mobile, it's best to do as little as possible by default.

[antonfirsov]

f you point me to the commits I need to test

If we suspect metrics, you need to check #89985 #87319

Note that Meter and Instrument were designed in a way that there is no way to opt-out of their instantiation, since users can opt-in into measurements per-instrument at runtime.

If this has to be revisited, and we need global switch(es) to turn the entire feature on/off (per library? for the entire BCL?) you need to discuss it with @noahfalk.

[MihaZupan]

When nothing is listening to metrics (the default), the overhead on an individual request should be negligible (we'll do a quick check to see if anything is listening and then skip all the extra logic).

As Anton said though, someone may start collecting this information at any time, so the HttpClient instrumentation has to do some work at startup to prepare for that possibility.
This startup cost is mainly creating the shared Meter instance, and creating a few Instruments from it.

28a4c95 was the initial commit that added this logic to HttpClient. There have been a few changes to that logic in main since, but they shouldn't meaningfully affect startup costs.