[mono][perf] iOS disk size regression on 11 Nov 2022

[kotlarmilos]

Description

Microbenchmark improvement #78182 introduced concrete instances in addition to the gshared methods in AOT mode to optimize #78163.

For Mono iOS sample app, binary disk size (SOD) has increased by 8%.

Filename	SOD without concrete instances (80208e6)	SOD with concrete instances (486682a)
HelloiOS	17382408 bytes	18872480 bytes

Number of symbols has increased by 5k.

Filename	Number of symbols without concrete instances (80208e6)	Number of symbols with concrete instances (486682a)
HelloiOS	80007	85179

---

At the same time 80208e6 excluded dynamic libraries from the bundle as static linking is used.

For Mono iOS sample app, SOD has decreased by 5%.

File	Value (bytes)
HelloiOS	17042528
Info.plist	980
PkgInfo	8
Program.aotdata	4792
Program.deps.json	11754
Program.dll	6656
Program.runtimeconfig.json	1064
System.Console.aotdata	41952
System.Console.dll	17408
System.Private.CoreLib.aotdata	826296
System.Private.CoreLib.dll	998912
icudt.dat	1824544
icudt_CJK.dat	956416
icudt_EFIGS.dat	550320
icudt_no_CJK.dat	1071600
(EXCLUDED) libSystem.IO.Compression.Native.dylib	877152
(EXCLUDED) libSystem.Native.dylib	145728
(EXCLUDED) libSystem.Net.Security.Native.dylib	72064
(EXCLUDED) libSystem.Security.Cryptography.Native.Apple.dylib	104384

cc @ivanpovazan

Configuration

OS: iOS
Architecture: arm64
.NET version: 7.0.100-rc.1.22431.12

[dotnet-issue-labeler]

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.

[ivanpovazan]

@kotlarmilos if this affected Mono iOS sample size it probably regressed MAUI iOS sizes as well.
Do you know if this is being tracked already?

[kotlarmilos]

Good point, #78182 is not backported to .net7 so the regression is not present in MAUI iOS size measurements. I haven't found an issue related to the regression in MAUI iOS.

[ivanpovazan]

/cc @jonathanpeppers

[vargaz]

So the extra methods look to be Vector/Scalar method instances, these were previously shared, but now we generate specialized instances for them, leading to the size increase.

[vargaz]

Most of these methods appear to be the fallback methods in case SIMD is not found. If SIMD is enabled on ios, then this code will not be called, if it's not enabled, then the app should not call it since the performance is not good. So there should be a way to avoid generating code for them.

[kotlarmilos]

Related issues:

#71430
#71431

[ivanpovazan]

Most of these methods appear to be the fallback methods in case SIMD is not found. If SIMD is enabled on ios, then this code will not be called, if it's not enabled, then the app should not call it since the performance is not good. So there should be a way to avoid generating code for them.

@vargaz just to clarify, are you suggesting that:

• if SIMD is enabled -> do not generate extra instances (leave codegen as is - falling back to GSHAREDVTs)
• if SIMD is disabled -> generate extra instances to improve performance

[vargaz]

If SIMD is enabled, then these methods are never going to be called. So putting a
if (!SIMDIsEnabled) else , and having either the linker or the aot compiler eliminate the if (!SIMDIsEnabled) conditional would make sure that even if these instances are aot-ed, then the method bodies will be very small, just a throw.

[ivanpovazan]

If I am understanding this correctly, something similar was attempted here: #71430 (comment)
where in my experimentation I tried to exclude Scalar fallbacks, which turned out to be impossible -> ie software fallbacks are needed even on arm64 architectures.
Am I missing the point?

[vargaz]

Was just an idea, not sure whenever it will work.

[ivanpovazan]

I guess this comment: dotnet/perf-autofiling-issues#9599 (comment) goes along with what Zoltan said. If I understand correctly, before going further, we would need to have SIMD work completed on the Mono side.

[fanyang-mono]

All the SIMD support that we added so far should be fully enabled for full AOT mode, which is what iOS is using. @vargaz Are the size increase here caused by code patterns involving generics, which used to be generated into a gsharedvt function, now generated into concrete type instances to facilitate the previous performance regression?

[vargaz]

Previously, we were emitting shared methods, now we emit the same shared methods (to handle all cases) and concrete instances as well (for better performance).

[ghost]

Tagging subscribers to 'size-reduction': @eerhardt, @SamMonoRT, @marek-safar
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Microbenchmark improvement #78182 introduced concrete instances in addition to the gshared methods in AOT mode to optimize #78163.

For Mono iOS sample app, binary disk size (SOD) has increased by 8%.

Filename	SOD without concrete instances (80208e6)	SOD with concrete instances (486682a)
HelloiOS	17382408 bytes	18872480 bytes

Number of symbols has increased by 5k.

Filename	Number of symbols without concrete instances (80208e6)	Number of symbols with concrete instances (486682a)
HelloiOS	80007	85179

---

At the same time 80208e6 excluded dynamic libraries from the bundle as static linking is used.

For Mono iOS sample app, SOD has decreased by 5%.

File	Value (bytes)
HelloiOS	17042528
Info.plist	980
PkgInfo	8
Program.aotdata	4792
Program.deps.json	11754
Program.dll	6656
Program.runtimeconfig.json	1064
System.Console.aotdata	41952
System.Console.dll	17408
System.Private.CoreLib.aotdata	826296
System.Private.CoreLib.dll	998912
icudt.dat	1824544
icudt_CJK.dat	956416
icudt_EFIGS.dat	550320
icudt_no_CJK.dat	1071600
(EXCLUDED) libSystem.IO.Compression.Native.dylib	877152
(EXCLUDED) libSystem.Native.dylib	145728
(EXCLUDED) libSystem.Net.Security.Native.dylib	72064
(EXCLUDED) libSystem.Security.Cryptography.Native.Apple.dylib	104384

cc @ivanpovazan

Configuration

OS: iOS
Architecture: arm64
.NET version: 7.0.100-rc.1.22431.12

Author:	kotlarmilos
Assignees:	vargaz, kotlarmilos
Labels:	tenet-performance, area-Codegen-AOT-mono, size-reduction
Milestone:	8.0.0