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Commit 9dbc491a authored by Tri Dao's avatar Tri Dao
Browse files

Rename, add benchmarking script

parent 1fcbe6f0
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Alpha release of FlashAttention. ## FlashAttention - Alpha release (0.1).
To compile: To compile (requiring NVCC and an A100 GPU):
``` ```
cd csrc/stream_attn cd csrc/flash_attn
python setup.py install python setup.py install
``` ```
Interface: `streaming_attention.py` Interface: `flash_attention.py`
Contact: `trid@stanford.edu` To run the benchmark against PyTorch standard attention:
```
PYTHONPATH=$PWD python benchmarks/benchmark_flash_attention.py
```
FlashAttention currently supports:
1. A100 GPUs.
2. fp16.
3. Head dimensions 16, 32, 64.
Our roadmap to broaden the support:
1. Refactor to use Cutlass.
2. Support SM86 GPUs (e.g. RTX 3080, 3090), support SM75 GPUs (e.g. T4).
3. Support bf16.
4. Support head dimension 128.
5. Make package pip-installable.
6. Support SM70 GPUs (V100).
7. Fused rotary embedding.
8. Attention linear bias (e.g. ALiBi).
### Acknowledgments
Our implementation uses Apex's
[FMHA](https://github.com/NVIDIA/apex/tree/master/apex/contrib/csrc/fmha) code
as a starting point.
We thank [Young-Jun Ko](https://yjk21.github.io/) for the in-depth explanation of his FMHA implementation
and for his thoughtful answers to our questions about CUDA.
from functools import partial
import math
import torch
import torch.nn as nn
import torch.nn.functional as F
from einops import rearrange, repeat
from benchmarks.utils import benchmark_all, benchmark_forward, benchmark_backward, benchmark_combined
from bert_padding import unpad_input, pad_input
from flash_attn_interface import flash_attn_func
def attention_ref(qkv, attn_mask, dropout_p, upcast=False, causal=False):
"""
Arguments:
qkv: (batch_size, seqlen, 3, nheads, head_dim)
attn_mask: (batch_size, seqlen)
dropout_p: float
Output:
output: (batch_size, seqlen, nheads, head_dim)
attention: softmax after dropout
"""
q, k, v = (qkv.float() if upcast else qkv).unbind(dim=2)
seqlen = qkv.shape[1]
d = qkv.shape[-1]
scores = torch.einsum('bthd,bshd->bhts', q, k / math.sqrt(d))
scores.masked_fill_(rearrange(~attn_mask, 'b s -> b 1 1 s'), float('-inf'))
if causal:
causal_mask = torch.triu(torch.ones(seqlen, seqlen, dtype=torch.bool, device=qkv.device), 1)
scores.masked_fill_(causal_mask, float('-inf'))
attention = torch.softmax(scores, dim=-1)
attention_drop = F.dropout(attention, dropout_p)
output = torch.einsum('bhts,bshd->bthd', attention_drop , v)
# return output.to(dtype=qkv.dtype), attention.to(dtype=qkv.dtype)
return output.to(dtype=qkv.dtype)
torch.manual_seed(0)
repeats = 30
batch_size = 64
nheads = 16
seqlen = 1024
n = 1024
d = n // nheads
dropout_p = 0.1
causal = False
dtype = torch.float16
device = 'cuda'
x = torch.randn(batch_size, seqlen, n, device='cuda', dtype=dtype, requires_grad=True)
Wqkv = torch.nn.Linear(nheads * d, 3 * nheads * d, device=device, dtype=dtype)
lengths = torch.randint(seqlen - 20, seqlen, (batch_size, 1), device='cuda')
attention_mask_bool = repeat(torch.arange(seqlen, device='cuda'), 's -> b s', b=batch_size) < lengths
attention_mask = torch.zeros(batch_size, seqlen, device='cuda', dtype=dtype)
attention_mask[~attention_mask_bool] = -10000.0
attention_mask = rearrange(attention_mask, 'b s -> b 1 1 s')
x_unpad, indices, cu_seqlens, max_seqlen_in_batch = unpad_input(x, attention_mask_bool)
qkv_unpad = rearrange(Wqkv(x_unpad), 'nnz (t h d) -> nnz t h d', t=3,
h=nheads).detach().requires_grad_()
qkv = rearrange(Wqkv(x), 'b s (t h d) -> b s t h d', t=3, h=nheads).detach().requires_grad_()
fn = lambda qkv_unpad: flash_attn_func(qkv_unpad, cu_seqlens, dropout_p, max_seqlen_in_batch, causal=causal)
benchmark_all(fn, qkv_unpad, repeats=repeats, desc='FlashAttention')
fn = lambda qkv: attention_ref(qkv, attention_mask_bool, dropout_p, causal=causal)
benchmark_all(fn, qkv, repeats=repeats, desc='PyTorch Standard Attention')
# Adapted from https://github.com/HazyResearch/hippo/blob/datasets/benchmark/utils.py
""" Useful functions for writing test code. """
import torch
import torch.utils.benchmark as benchmark
def benchmark_forward(fn, *inputs, min_run_time = 0.2, repeats = 10, desc='', verbose=True, **kwinputs):
""" Use Pytorch Benchmark on the forward pass of an arbitrary function. """
if verbose:
print(desc, '- Forward pass')
t = benchmark.Timer(
stmt='fn(*inputs, **kwinputs)',
globals={'fn': fn, 'inputs': inputs, 'kwinputs': kwinputs},
num_threads=torch.get_num_threads(),
)
m = t.timeit(repeats)
if verbose:
print(m)
return t, m
def benchmark_backward(fn, *inputs, grad=None, repeats=10, desc='', verbose=True, **kwinputs):
""" Use Pytorch Benchmark on the backward pass of an arbitrary function. """
if verbose:
print(desc, '- Backward pass')
y = fn(*inputs, **kwinputs)
if type(y) is tuple:
y = y[0]
if grad is None:
grad = torch.randn_like(y)
else:
if grad.shape != y.shape:
raise RuntimeError('Grad shape does not match output shape')
t = benchmark.Timer(
stmt='y.backward(grad, retain_graph=True)',
globals={'y': y, 'grad': grad},
num_threads=torch.get_num_threads(),
)
m = t.timeit(repeats)
if verbose:
print(m)
return t, m
def benchmark_combined(fn, *inputs, grad=None, repeats=10, desc='', verbose=True, **kwinputs):
""" Use Pytorch Benchmark on the forward+backward pass of an arbitrary function. """
if verbose:
print(desc, '- Forward + Backward pass')
# y = fn(*inputs, **kwinputs)
# if grad is None:
# grad = torch.randn_like(y)
# else:
# if grad.shape != y.shape:
# raise RuntimeError('Grad shape does not match output shape')
# del y
def f(grad, *inputs, **kwinputs):
y = fn(*inputs, **kwinputs)
if type(y) is tuple:
y = y[0]
if grad is None:
grad = torch.randn_like(y)
else:
if grad.shape != y.shape:
raise RuntimeError('Grad shape does not match output shape')
y.backward(grad, retain_graph=True)
t = benchmark.Timer(
stmt='f(grad, *inputs, **kwinputs)',
globals={'f': f, 'fn': fn, 'inputs': inputs, 'grad': grad, 'kwinputs': kwinputs},
num_threads=torch.get_num_threads(),
)
m = t.timeit(repeats)
if verbose:
print(m)
return t, m
def benchmark_all(fn, *inputs, grad=None, repeats=10, desc='', verbose=True, **kwinputs):
""" Use Pytorch Benchmark on the forward+backward pass of an arbitrary function. """
return (
benchmark_forward(fn, *inputs, repeats=repeats, desc=desc, verbose=verbose, **kwinputs),
benchmark_backward(fn, *inputs, grad=grad, repeats=repeats, desc=desc, verbose=verbose,
**kwinputs),
benchmark_combined(fn, *inputs, grad=grad, repeats=repeats, desc=desc, verbose=verbose,
**kwinputs),
)
def pytorch_profiler(fn, *inputs, repeats=10):
""" Wrap benchmark functions in Pytorch profiler to see CUDA information. """
with torch.profiler.profile(
activities=[
torch.profiler.ProfilerActivity.CPU,
torch.profiler.ProfilerActivity.CUDA,
],
record_shapes=True,
profile_memory=True,
with_stack=True,
) as p:
# benchmark_forward(repeats, fn, *inputs)
fn(*inputs)
print(p.key_averages().table(
sort_by="self_cuda_time_total", row_limit=-1))
def convert_data(*tensors, device='cuda'):
tensors = tuple(t.to(device) for t in tensors)
for t in tensors:
if t.is_leaf: t.requires_grad = True
t.retain_grad()
return tensors
def log_backward(output, *inputs):
""" Perform backward pass of output and print gradients of input tensors. """
#print(f"{output=}")
output.sum().backward(retain_graph=True)
print("Gradients:")
for t in inputs:
print(t.grad)
t.grad.zero_()
def benchmark_memory(fn, *inputs, desc='', verbose=True, **kwinputs):
torch.cuda.empty_cache()
torch.cuda.reset_peak_memory_stats()
torch.cuda.synchronize()
fn(*inputs, **kwinputs)
torch.cuda.synchronize()
mem = torch.cuda.max_memory_allocated() / ((2 ** 20) * 1000)
if verbose:
print(f'{desc} max memory: ', mem)
torch.cuda.empty_cache()
return mem
...@@ -95,18 +95,18 @@ torch_dir = torch.__path__[0] ...@@ -95,18 +95,18 @@ torch_dir = torch.__path__[0]
if os.path.exists(os.path.join(torch_dir, "include", "ATen", "CUDAGeneratorImpl.h")): if os.path.exists(os.path.join(torch_dir, "include", "ATen", "CUDAGeneratorImpl.h")):
generator_flag = ["-DOLD_GENERATOR_PATH"] generator_flag = ["-DOLD_GENERATOR_PATH"]
raise_if_cuda_home_none("--streamattn") raise_if_cuda_home_none("--flashattn")
# Check, if CUDA11 is installed for compute capability 8.0 # Check, if CUDA11 is installed for compute capability 8.0
cc_flag = [] cc_flag = []
_, bare_metal_major, _ = get_cuda_bare_metal_version(CUDA_HOME) _, bare_metal_major, _ = get_cuda_bare_metal_version(CUDA_HOME)
if int(bare_metal_major) < 11: if int(bare_metal_major) < 11:
raise RuntimeError("--streamattn only supported on SM80+") raise RuntimeError("--flashattn only supported on SM80+")
cc_flag.append("-gencode") cc_flag.append("-gencode")
cc_flag.append("arch=compute_80,code=sm_80") cc_flag.append("arch=compute_80,code=sm_80")
ext_modules.append( ext_modules.append(
CUDAExtension( CUDAExtension(
name="stream_attn_cuda", name="flash_attn_cuda",
sources=[ sources=[
"fmha_api.cpp", "fmha_api.cpp",
"src/fmha_fprop_fp16_kernel.sm80.cu", "src/fmha_fprop_fp16_kernel.sm80.cu",
...@@ -139,9 +139,9 @@ ext_modules.append( ...@@ -139,9 +139,9 @@ ext_modules.append(
) )
setup( setup(
name="stream_attn_cuda", name="flash_attn_cuda",
version="0.1", version="0.1",
description="Streaming attention", description="Flash Attention",
ext_modules=ext_modules, ext_modules=ext_modules,
cmdclass={"build_ext": BuildExtension} if ext_modules else {}, cmdclass={"build_ext": BuildExtension} if ext_modules else {},
) )
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