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CPU Optimizations for FP8 #2559
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Signed-off-by: Varun Thumbe <[email protected]>
for more information, see https://pre-commit.ci
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations Signed-off-by: Varun Thumbe <[email protected]>
for more information, see https://pre-commit.ci
|
/te-ci L1 pytorch |
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations Signed-off-by: Varun Thumbe <[email protected]>
|
/te-ci L1 pytorch |
Greptile SummaryThis PR implements CPU optimizations for FP8 operations by reducing Python/C++ overhead through several techniques:
Confidence Score: 4/5
Important Files Changed
Sequence DiagramsequenceDiagram
participant User as User Code
participant Linear as Linear Module
participant QT as QuantizedTensor
participant Quantizer as C++ Quantizer
participant PyAPI as Python C API
User->>Linear: forward(inp, weight, bias)
Note over Linear: Cache requires_grad values early
Linear->>QT: Access dtype, requires_grad
Note over QT: Return cached values (fast path)
Linear->>Quantizer: create_tensor()
Quantizer->>Quantizer: Compute stride in C++
Quantizer->>PyAPI: PyDict_New(), PyObject_Call()
Note over PyAPI: Direct C API bypasses pybind11 overhead
PyAPI-->>Quantizer: Float8Tensor instance
Quantizer-->>Linear: TensorWrapper + py::object
Linear->>QT: Access shape, is_cuda
Note over QT: Return from internal _data/_transpose
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Additional Comments (3)
-
transformer_engine/pytorch/csrc/util.cpp, line 18-20 (link)logic: Critical logical error:
||should be&&. This condition will always betruesince a value cannot simultaneously be both scaling modes, causing the function to always return nullopt for valid inputs. -
transformer_engine/pytorch/quantized_tensor.py, line 373-393 (link)style: commented-out code for
requires_gradcaching optimization - consider removing dead code entirely. Is this code planned to be implemented later or should it be removed?Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!
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transformer_engine/pytorch/module/linear.py, line 484 (link)logic: Logical error: this condition should use OR (||) not AND (&&). The original logic was checking if ANY tensor requires gradients for FP8 handling, but this now only activates when ALL three require gradients, including bias which may be None.
Should the FP8 condition check if any tensor requires gradients (OR logic) rather than all tensors (AND logic)?
10 files reviewed, 3 comments
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations Signed-off-by: Varun Thumbe <[email protected]>
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/te-ci L1 pytorch |
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Greptile Overview
Greptile Summary
This PR implements CPU-side performance optimizations for FP8 operations by caching frequently accessed attributes and reducing redundant function calls. The optimizations target expensive PyObject attribute lookups on custom tensor types and repeated C++ function calls.
Key Changes:
- Caches
requires_grad,dtype,shape, andis_cudaattribute accesses to avoid expensive PyObject lookups on custom tensors - Reorders attribute checks in
get_tensor_device()to prioritize internal quantized tensor attributes - Makes
num_devicesstatic innvte_is_non_tn_fp8_gemm_supported()to cache device count - Stores GEMM support check results in local variables to avoid redundant function calls
Critical Issues Found:
- Variable redeclaration error in
cublaslt_gemm.cu(line 224) will prevent compilation - Logic bug in
linear.py(line 484) changes FP8 state management from OR logic to AND logic, breaking functionality when bias is None or doesn't require grad
Confidence Score: 0/5
- This PR cannot be merged due to compilation error and critical logic bug
- Two critical issues prevent merging: (1) C++ compilation will fail due to variable redeclaration at line 224 of cublaslt_gemm.cu, and (2) logic bug at line 484 of linear.py breaks FP8 state management by requiring all three tensors to have requires_grad=True instead of any one of them
- Pay close attention to
transformer_engine/common/gemm/cublaslt_gemm.cu(compilation error) andtransformer_engine/pytorch/module/linear.py(logic bug)
Important Files Changed
File Analysis
| Filename | Score | Overview |
|---|---|---|
| transformer_engine/common/gemm/cublaslt_gemm.cu | 1/5 | Caches function call result to reduce overhead, but contains variable redeclaration error that will cause compilation failure |
| transformer_engine/common/transformer_engine.cpp | 5/5 | Makes num_devices static to avoid redundant calls to cuda::num_devices() - valid optimization |
| transformer_engine/pytorch/module/linear.py | 0/5 | Caches requires_grad checks for performance, but contains critical logic bug at line 484 that changes FP8 state management behavior |
Sequence Diagram
sequenceDiagram
participant User as User Code
participant Linear as Linear Module
participant Quantizer as Quantizer/QuantizedTensor
participant GEMM as GEMM Operations
participant CPP as C++ Extensions
Note over Linear,CPP: Performance Optimization Flow
User->>Linear: forward(input, weight, bias)
Note over Linear: Cache requires_grad checks
Linear->>Linear: inp_requires_grad = inp.requires_grad<br/>weight_requires_grad = weight.requires_grad<br/>bias_requires_grad = bias.requires_grad
Linear->>Quantizer: Check if quantized tensor
alt QuantizedTensor
Note over Quantizer: Use cached dtype property
Quantizer->>Quantizer: return self._dtype
Note over Quantizer: Use cached shape/is_cuda
Quantizer->>Quantizer: return self._data.shape
else Regular Tensor
Quantizer->>Linear: Standard attribute access
end
Linear->>CPP: get_tensor_device(tensor)
Note over CPP: Reordered attribute checks
CPP->>CPP: Check _rowwise_data first<br/>Check _columnwise_data<br/>Check device last
CPP-->>Linear: device_index
Linear->>GEMM: Configure GEMM parameters
Note over GEMM: Cache nvte_is_non_tn_fp8_gemm_supported
GEMM->>CPP: nvte_is_non_tn_fp8_gemm_supported()
Note over CPP: Static num_devices cached
CPP-->>GEMM: support_flag
GEMM->>GEMM: Store in local variable
GEMM->>GEMM: Execute optimized GEMM
GEMM-->>Linear: output
Note over Linear: FP8 State Management
alt FP8 enabled and requires_grad check
Linear->>Linear: Update FP8 tensors<br/>based on cached flags
end
Linear-->>User: output
Additional Comments (2)
|
Signed-off-by: Varun Thumbe <[email protected]>
|
/te-ci L1 pytorch |
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/te-ci L1 pytorch |
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8 files reviewed, 8 comments
| ret.A_scale_inv = A.scale_inv.dptr; | ||
| ret.lda = is_A_transposed ? k : m; | ||
| if (!nvte_is_non_tn_fp8_gemm_supported() && !is_A_transposed) { | ||
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); |
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Variable is_nvte_non_tn_fp8_gemm_supported is redeclared in the same scope - it was already declared at line 224 for the B matrix configuration. This causes a compilation error or shadowing issue.
The variable should only be declared once at the beginning of the function scope and reused for both A and B matrix configurations.
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); | |
| // Move this declaration before line 125 (Configure A matrix) | |
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); |
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | ||
| PyTuple_New(0), kwargs); |
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Memory leak: PyTuple_New(0) creates a new Python tuple object with a reference count of 1, but this reference is never decremented. The tuple is passed directly to PyObject_Call which doesn't steal the reference, so it must be explicitly released.
This same issue occurs at lines 186, 398, 417, 697, 718, 1039, 1058, 1346, and 1367.
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | |
| PyTuple_New(0), kwargs); | |
| PyObject* args = PyTuple_New(0); | |
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | |
| args, kwargs); | |
| Py_DECREF(args); | |
| Py_DECREF(kwargs); |
| PyDict_SetItemString(kwargs, "fp8_dtype", py::cast(this->dtype).ptr()); | ||
| PyDict_SetItemString(kwargs, "data_transpose", transpose_py.ptr()); | ||
| PyDict_SetItemString(kwargs, "quantizer", this->quantizer.ptr()); | ||
| PyDict_SetItemString(kwargs, "device", py::cast(device).ptr()); |
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Invalid parameter: The Float8TensorStorage.__new__ method does not accept a device parameter. Looking at the Python class definition in float8_tensor_storage.py, the __new__ signature only expects: data, fp8_scale_inv, fp8_dtype, data_transpose, and quantizer.
This will cause a runtime error when trying to create Float8TensorStorage instances. This issue also occurs at lines 184, 396, 415, and in similar patterns for MXFP8 and other quantizers.
| PyDict_SetItemString(kwargs, "device", py::cast(device).ptr()); | |
| // Remove this line - device parameter is not accepted | |
| // PyDict_SetItemString(kwargs, "device", py::cast(device).ptr()); |
| PyTypeObject *NVFP4TensorPythonClass = nullptr; | ||
| PyTypeObject *NVFP4TensorStoragePythonClass = nullptr; | ||
| PyTypeObject *NVFP4QuantizerClass = nullptr; | ||
| bool is_extension_initialized = false; |
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Race condition: The is_extension_initialized flag is not thread-safe. If init_extension() is called concurrently from multiple threads, both threads could pass the check at line 105 before either sets the flag at line 110, causing the initialization code to run multiple times.
The original implementation using null-checks on the individual class pointers was safer because Python's module import system provides thread safety. Consider using std::once_flag and std::call_once for proper thread-safe initialization:
| bool is_extension_initialized = false; | |
| bool is_extension_initialized = false; | |
| std::once_flag extension_init_flag; |
And in init_extension():
void init_extension() {
std::call_once(extension_init_flag, []() {
init_float8_extension();
init_mxfp8_extension();
init_float8blockwise_extension();
init_nvfp4_extensions();
});
}| static int num_devices = transformer_engine::cuda::num_devices(); | ||
| static std::vector<int> cache(num_devices, -1); | ||
| static std::vector<std::once_flag> flags(num_devices); |
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Potential edge case: The num_devices is captured once as a static variable, so if the number of devices changes at runtime (e.g., with CUDA MPS or device enumeration changes), the cache and flags vectors could be undersized, leading to out-of-bounds access at line 968.
While dynamic device changes are rare, consider adding a bounds check:
| static int num_devices = transformer_engine::cuda::num_devices(); | |
| static std::vector<int> cache(num_devices, -1); | |
| static std::vector<std::once_flag> flags(num_devices); | |
| static int num_devices = transformer_engine::cuda::num_devices(); | |
| static std::vector<int> cache(num_devices, -1); | |
| static std::vector<std::once_flag> flags(num_devices); | |
| int device_id = transformer_engine::cuda::current_device(); | |
| NVTE_CHECK(device_id < num_devices, "Device ID exceeds cached device count"); |
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4 files reviewed, 4 comments
| ret.B_scale_inv = B.scale_inv.dptr; | ||
| ret.ldb = is_B_transposed ? n : k; | ||
| if (!nvte_is_non_tn_fp8_gemm_supported() && is_B_transposed) { | ||
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); |
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Variable is_nvte_non_tn_fp8_gemm_supported is redeclared in the same function scope (already declared at line 132). In C++, this is a compilation error. The variable should be declared once at the function scope level before both the A matrix and B matrix configuration blocks.
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); | |
| // Move declaration to line 104 (after GemmParam ret;) to avoid redeclaration |
| py::object scale_inv_py = py::cast(scale_inv); | ||
| // Initialize scale-inverse tensor | ||
| if (!scale_inv) { | ||
| scale_inv = at::reciprocal(scale); | ||
| } |
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Critical bug: scale_inv_py is created on line 146 by dereferencing scale_inv (which is std::optional<at::Tensor>), but scale_inv is only initialized on lines 148-150 if it's empty. When scale_inv is not provided to this function, line 146 will dereference an empty optional, causing undefined behavior or a crash.
The fix is to move line 146 after the initialization block:
| py::object scale_inv_py = py::cast(scale_inv); | |
| // Initialize scale-inverse tensor | |
| if (!scale_inv) { | |
| scale_inv = at::reciprocal(scale); | |
| } | |
| py::object transpose_py = with_transpose ? py::cast(*transpose) : py::none(); | |
| // Initialize scale-inverse tensor | |
| if (!scale_inv) { | |
| scale_inv = at::reciprocal(scale); | |
| } | |
| py::object scale_inv_py = py::cast(*scale_inv); |
| PyDict_SetItemString(kwargs, "device", py::cast(device).ptr()); | ||
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| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | ||
| PyTuple_New(0), kwargs); |
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Memory leak: PyTuple_New(0) creates a new tuple with reference count 1, but PyObject_Call does not steal the reference. The tuple must be stored and explicitly DECREF'd after the call. This pattern is repeated 12 times throughout this file (lines 166, 186, 398, 417, 697, 718, 1039, 1058, 1346, 1367).
| PyTuple_New(0), kwargs); | |
| PyObject* args = PyTuple_New(0); | |
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | |
| args, kwargs); | |
| Py_DECREF(args); |
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations Signed-off-by: Varun Thumbe <[email protected]>
Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com> Signed-off-by: vthumbe1503 <[email protected]>
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13 files reviewed, 13 comments
| ret.B_scale_inv = B.scale_inv.dptr; | ||
| ret.ldb = is_B_transposed ? n : k; | ||
| if (!nvte_is_non_tn_fp8_gemm_supported() && is_B_transposed) { | ||
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); |
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[P0] Variable is_nvte_non_tn_fp8_gemm_supported is already declared at line 132. Declaring it again here causes a compilation error. Remove this declaration and reuse the variable from line 132.
| int is_nvte_non_tn_fp8_gemm_supported = nvte_is_non_tn_fp8_gemm_supported(); | |
| // Reuse is_nvte_non_tn_fp8_gemm_supported from line 132 |
| } | ||
| py::object transpose_py = with_transpose ? py::cast(*transpose) : py::none(); | ||
|
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| py::object transpose_py = with_transpose ? py::cast(*transpose) : py::none(); |
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[P0] Use-after-free bug: scale_inv_py is created from scale_inv before scale_inv is initialized. When scale_inv parameter is empty (lines 148-150), this dereferences an empty std::optional, causing undefined behavior. Move this line after the scale_inv initialization.
| py::object transpose_py = with_transpose ? py::cast(*transpose) : py::none(); | |
| // Move scale_inv_py creation after initialization (line 150) |
| PyDict_SetItemString(kwargs, "quantizer", this->quantizer.ptr()); | ||
| PyDict_SetItemString(kwargs, "device", py::cast(device).ptr()); | ||
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| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), |
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[P0] Memory leak: PyTuple_New(0) creates a new Python object with refcount 1, but it's never decremented. This leaks memory on every tensor creation. Add Py_DECREF for the tuple:
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), | |
| PyObject* args = PyTuple_New(0); | |
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8TensorStoragePythonClass), args, kwargs); | |
| Py_DECREF(args); |
| PyDict_SetItemString(kwargs, "is_2D_scaled", py::cast(block_scaling_dim == 2).ptr()); | ||
| PyDict_SetItemString(kwargs, "data_format", py::cast(data_format).ptr()); | ||
|
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||
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(Float8BlockwiseQTensorPythonClass), |
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[P0] Memory leak: PyTuple_New(0) is not decremented (same pattern as line 166).
| PyDict_SetItemString(kwargs, "fp8_dtype", py::cast(this->dtype).ptr()); | ||
| PyDict_SetItemString(kwargs, "quantizer", this->quantizer.ptr()); | ||
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| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(MXFP8TensorStoragePythonClass), |
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[P0] Memory leak: PyTuple_New(0) is not decremented (same pattern as line 166).
| PyDict_SetItemString(kwargs, "fp4_dtype", py::cast(this->dtype).ptr()); | ||
| PyDict_SetItemString(kwargs, "quantizer", this->quantizer.ptr()); | ||
|
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||
| PyObject* result = PyObject_Call(reinterpret_cast<PyObject*>(NVFP4TensorStoragePythonClass), |
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[P0] Memory leak: PyTuple_New(0) is not decremented (same pattern as line 166).
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11 files reviewed, 1 comment
| @dtype.setter | ||
| def dtype(self, value: torch.dtype) -> None: | ||
| """Set dtype property""" | ||
| # Update the cached value | ||
| self._dtype = value | ||
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") |
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logic: The warning is emitted unconditionally, but this setter is called in Float8Tensor._set_data, MXFP8Tensor._set_data, and NVFP4Tensor._set_data during normal copy operations when any tensor attribute differs (size, stride, device, etc.), not just dtype. This will cause spurious warnings.
Consider only warning when the value actually changes:
| @dtype.setter | |
| def dtype(self, value: torch.dtype) -> None: | |
| """Set dtype property""" | |
| # Update the cached value | |
| self._dtype = value | |
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| @dtype.setter | |
| def dtype(self, value: torch.dtype) -> None: | |
| """Set dtype property""" | |
| # Update the cached value | |
| if hasattr(self, "_dtype") and self._dtype != value: | |
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| self._dtype = value |
Signed-off-by: Varun Thumbe <[email protected]>
Signed-off-by: Varun Thumbe <[email protected]>
Signed-off-by: Varun Thumbe <[email protected]>
for more information, see https://pre-commit.ci
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11 files reviewed, 1 comment
| @dtype.setter | ||
| def dtype(self, value: torch.dtype) -> None: | ||
| """Set dtype property""" | ||
| # Update the cached value | ||
| self._dtype = value | ||
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") |
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logic: The dtype setter unconditionally emits a warning, but this setter is called in normal _set_data operations (e.g., float8_tensor.py:1004, mxfp8_tensor.py:789, nvfp4_tensor.py:693) during legitimate tensor copy operations. This will cause spurious warnings every time tensor data is copied.
Consider only warning when the value actually changes:
| @dtype.setter | |
| def dtype(self, value: torch.dtype) -> None: | |
| """Set dtype property""" | |
| # Update the cached value | |
| self._dtype = value | |
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| @dtype.setter | |
| def dtype(self, value: torch.dtype) -> None: | |
| """Set dtype property""" | |
| # Update the cached value | |
| if hasattr(self, "_dtype") and self._dtype != value: | |
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| self._dtype = value |
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations
for more information, see https://pre-commit.ci
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/te-ci L1 pytorch |
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12 files reviewed, 3 comments
| static std::unordered_map<std::string, void *> symbol_cache; | ||
|
|
||
| // Check if symbol is already cached | ||
| auto it = symbol_cache.find(symbol); | ||
| FuncT *func; | ||
|
|
||
| if (it != symbol_cache.end()) { | ||
| func = reinterpret_cast<FuncT *>(it->second); | ||
| } else { | ||
| // Symbol not in cache, look it up and cache the result | ||
| void *ptr = get_symbol(symbol); | ||
| symbol_cache[symbol] = ptr; | ||
| func = reinterpret_cast<FuncT *>(ptr); |
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logic: Thread safety issue: The static unordered_map is accessed without synchronization. If call() is invoked concurrently from multiple threads with different symbols, concurrent reads/writes to the map can cause data races and undefined behavior.
Consider using a mutex or std::shared_mutex for thread-safe access:
static std::unordered_map<std::string, void *> symbol_cache;
static std::mutex cache_mutex;
std::lock_guard<std::mutex> lock(cache_mutex);
auto it = symbol_cache.find(symbol);
// ...| PyObject* args = PyTuple_New(0); | ||
| PyDict_SetItemString(kwargs, "data", data_py.ptr()); | ||
| PyDict_SetItemString(kwargs, "fp8_scale_inv", scale_inv_py.ptr()); | ||
| PyDict_SetItemString(kwargs, "fp8_dtype", py::cast(this->dtype).inc_ref().ptr()); |
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logic: Memory leak: inc_ref() increments the reference count, but PyDict_SetItemString also increments it. When the kwargs dict is destroyed via Py_DECREF, the objects inside get one decref, leaving them with an extra reference that's never released.
Fix by storing the py::object in a local variable:
py::object fp8_dtype_obj = py::cast(this->dtype);
PyDict_SetItemString(kwargs, "fp8_dtype", fp8_dtype_obj.ptr());This pattern repeats throughout this file for all inc_ref() calls.
| """Set dtype property""" | ||
| # Update the cached value | ||
| self._dtype = value | ||
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") |
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logic: Spurious warning: The dtype setter unconditionally emits a warning, but it's called from _set_data() in Float8Tensor, MXFP8Tensor, and NVFP4Tensor during legitimate tensor copy operations. This will produce warnings in normal use.
Consider only warning when the value actually changes:
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| if hasattr(self, "_dtype") and self._dtype != value: | |
| warnings.warn("Dtype of QuantizedTensor has been changed. Ensure this is intended.") | |
| self._dtype = value |
Signed-off-by: Varun Thumbe <[email protected]>
Signed-off-by: Varun Thumbe <[email protected]>
Signed-off-by: vthumbe1503 <[email protected]>
for more information, see https://pre-commit.ci
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12 files reviewed, 1 comment
Signed-off-by: Varun Thumbe <[email protected]>
Signed-off-by: Varun Thumbe <[email protected]>
for more information, see https://pre-commit.ci
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12 files reviewed, 1 comment
| return self._data.shape | ||
| if self._transpose is not None: | ||
| transpose_shape = self._transpose.shape | ||
| return tuple(transpose_shape[1:]) + (transpose_shape[0],) |
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style: Returns tuple instead of torch.Size when computed from transpose, while self._data.shape returns torch.Size. Consider wrapping with torch.Size() for type consistency:
| return tuple(transpose_shape[1:]) + (transpose_shape[0],) | |
| return torch.Size(tuple(transpose_shape[1:]) + (transpose_shape[0],)) |
Signed-off-by: Varun Thumbe <[email protected]>
…ormerEngine into cpu_fp8_optimizations
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Signed-off-by: Varun Thumbe <[email protected]>
for more information, see https://pre-commit.ci
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/te-ci L1 pytorch |
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/te-ci L1 pytorch |
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/te-ci L1 pytorch |
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/te-ci L1 pytorch |
Description
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