kparzysz-quic commented on code in PR #71: URL: https://github.com/apache/tvm-rfcs/pull/71#discussion_r874091083
########## rfcs/0070-target-preprocessing.md: ########## @@ -0,0 +1,208 @@ +- Feature Name: target-architecture-preprocessor +- Start Date: 2022-04-04 +- RFC PR: [apache/tvm-rfcs#0070](https://github.com/apache/tvm-rfcs/pull/0000) +- GitHub Issue: [apache/tvm#0000](https://github.com/apache/tvm/issues/0000) + +# Summary +[summary]: #summary +Provide a standard and easily testable way to inspect architecture extensions and provide them to the various parts of TVM which utilise that information. + +# Motivation +[motivation]: #motivation +TVM has multiple ways to define a `Target`s architectural features for use in deciding on schedules or other calculations, here's a few different ways we do this: + +* CPU to Feature Mapping: https://github.com/apache/tvm/blob/d2db9cb0d839e32778f461b77e59f6418282a511/python/tvm/target/arm_isa.py#L22-L39 +* Inspecting `Target` in utility functions: https://github.com/apache/tvm/blob/d2db9cb0d839e32778f461b77e59f6418282a511/python/tvm/topi/arm_cpu/arm_utils.py#L24-L70 +* Inspecting `Target` in utility functions inside legalization code: https://github.com/apache/tvm/blob/02fbaf0ed9120a8f95155e63de42459f230584aa/python/tvm/relay/qnn/op/legalizations.py#L350-L359 +* Inspecting `Target` inside the definition a strategy: https://github.com/apache/tvm/blob/b542724873140bb051492530d97a78b9b7b7983d/python/tvm/relay/op/strategy/arm_cpu.py#L232 +* Processing bespoke Compiler arguments: https://github.com/apache/tvm/blob/d2db9cb0d839e32778f461b77e59f6418282a511/src/relay/backend/contrib/cmsisnn/compiler_attrs.cc#L47-L70 +* Registered as a `PackedFunc` (https://github.com/apache/tvm/blob/24e5498021cecca2fe7d44149ce90efe28b6d930/python/tvm/topi/x86/utils.py#L21-L34) and then used as part of `Op` processing: https://github.com/apache/tvm/blob/24e5498021cecca2fe7d44149ce90efe28b6d930/src/relay/qnn/op/requantize_config.h#L58-L73 + +This RFC aims to standardise the way in which we convert `Target` attributes into architectural features by processing them ahead of time. + +# Guide-level explanation +[guide-level-explanation]: #guide-level-explanation + +Two additional pre-processors can be added to the `Target`, for users to preprocess architectural information when the `Target` is created: +* Architecture Pre-processing - maps `Target` `attrs` to a new `arch` object +* Keys Pre-processing - maps `Target` `attrs` and `keys` to a new set of `keys` + +These new preprocessors will be illustrated using examples targeting TVM for Arm(R) Cortex(R)-M4. + +## Architecture Pre-processing +```c++ +Target("c") + .set_arch_preprocessor(MyArchPreprocessor) +``` + +This takes the `attrs` from `Target` and converts them into an object representing the architectural features of the `Target`, which can then be accessed using the `GetArch` method similar to `GetAttr`: + +```c++ +Target my_target("c -mcpu=cortex-m4"); +my_target->GetArch<Bool>("is_aarch64", false); // false +my_target->GetArch<Bool>("has_dsp", false); // true +``` + +```python +my_target = Target("c -mcpu=cortex-m4") +my_target.arch.is_aarch64 // false +my_target.arch.has_dsp // true +``` + +## Keys Pre-processing + +```c++ +Target("c") + .set_keys_preprocessor(MyKeysPreprocessor) +``` + +This takes the `attrs` from `Target` and maps them to relevant `keys` for use when selecting schedules: + +```c++ +Target my_target("c -mcpu=cortex-m4"); +my_target->keys; // ["arm_cpu", "cpu"] <-- "cpu" is taken from default keys and merged by the pre-preprocessor +``` + +# Reference-level explanation +[reference-level-explanation]: #reference-level-explanation + +Currently, there is a single `preprocessor` which takes an input of `attrs` and expects the same `attrs` returned with pre-processing applied: + +https://github.com/apache/tvm/blob/d2db9cb0d839e32778f461b77e59f6418282a511/src/target/target.cc#L810-L814 + +In extension to this, a series of new pre-processors will be defined: + +```c++ +using TargetAttrs = Map<String, ObjectRef>; +using TargetArch = Map<String, ObjectRef>; +using TargetKeys = Array<String>; + +using FTVMAttrPreprocessor = runtime::TypedPackedFunc<TargetAttrs(TargetAttrs)>; +using FTVMArchPreprocessor = runtime::TypedPackedFunc<TargetArch(TargetAttrs)>; +using FTVMKeysPreprocessor = runtime::TypedPackedFunc<TargetKeys(TargetAttrs, TargetKeys)>; +``` + +These implementations can be stored under `src/target/preprocessors/<arch_identifier>.{cc.h}` to allow them to be composed together such as: + +* src/target/preprocessors/aarch64.cc +* src/target/preprocessors/cpu.cc + +Where the `cpu` pre-processor can utilise the `aarch64` pre-processor if detected. + +## Rename Attr Preprocessor +To help avoid confusion between the existing `attrs` `preprocessor` and the new pre-processors, the `attrs` pre-processor will be renamed from `preprocessor` to `attr_preprocessor`: + +```c++ +class TargetKind { + ... + FTVMAttrPreprocessor attr_preprocessor; + + ... +} +``` + +## Architecture Preprocessor +The first new pre-processor, which processes `attrs` in to an `arch` object, is registered as a new field is added to `TargetKind`: + +```c++ +class TargetKind { + ... + FTVMArchPreprocessor arch_preprocessor; Review Comment: This would be equivalent to adding `arch` as an attribute, and setting it using the attribute preprocessor, wouldn't it? The difference here is that we don't access `arch` as an attribute, but as a member. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
