yanyanyanggg opened a new issue, #18562:
URL: https://github.com/apache/tvm/issues/18562
### Issue: [RISC-V RVV] Performance Degradation: ReLU activation slower with
vector extension
#### Description
The ReLU (rectified linear unit) operator shows significant performance
degradation with the RISC‑V Vector (RVV) extension. The acceleration ratio is
0.337, meaning the RVV version is about 3× slower than the scalar
implementation. This is unexpected for a simple elementwise operation that
should benefit greatly from vectorization.
#### Steps to Reproduce
1. Generate the ReLU operator with the following configuration:
```python
params = {
"dtype": "float32",
"batch": 14,
"channels": 23,
"input_height": 67,
"input_width": 99
}
```
2. Export the operator to two targets:
- **RV target** (scalar, without vector extension):
```
llvm -mtriple=riscv64-linux-gnu -mcpu=generic-rv64 -mabi=lp64d
-mattr=+64bit,+m,+a,+f,+d,+c
```
- **RVV target** (with vector extension):
```
llvm -mtriple=riscv64-linux-gnu -mcpu=generic-rv64 -mabi=lp64d
-mattr=+64bit,+m,+a,+f,+d,+c,+v
```
3. Run performance measurement on both targets.
Operator definition code:
```python
def export_relu(params, set_dir=None, platform="rv"):
data = relay.var("data",
shape=(params["batch"], params["channels"],
params["input_height"], params["input_width"]),
dtype=params["dtype"])
relu = relay.nn.relu(data)
export_op(relu, params["op_name"], [data], params, set_dir=set_dir)
```
#### Performance Data
- **RV execution time**: 7.945310 ms
- **RVV execution time**: 23.579300 ms
- **Acceleration ratio (RV/RVV)**: 0.337 (RVV is ~3× slower)
#### Environment Information
- **TVM version**: 0.19.0
- **LLVM version**: [Please provide: `llvm-config --version`]
- **Hardware**: Spacemit K1‑X bit‑brick board
- **CPU**: Spacemit X60 (8 cores, 1.6 GHz)
- **ISA**: rv64imafdcv (with vector extensions)
- **Memory**: 7.6 GB
- **OS**: Bianbu 2.2, Linux kernel 6.6.63
- **Operation**: Elementwise ReLU on ~1.7M elements
#### Expected Behavior
RVV vectorization should provide a performance improvement over the scalar
RV baseline for simple elementwise operations like ReLU.
#### Additional Context
- The ReLU operation is applied elementwise to a tensor of ~1.7M elements.
- The severe performance regression (3× slower) is particularly surprising
for such a simple operation that should be a perfect candidate for
vectorization.
- This issue is part of a broader pattern where multiple operators (sum,
log, relu, bias_add, sqrt, etc.) show significant performance degradation with
RVV, suggesting a potential systemic issue in TVM's RVV code generation or
optimization.
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