| """Honest GPU timing. Import `bench` rather than hand-rolling a timer. |
| |
| The failure this exists to prevent: an eager reference in this repo measured 185 ms wall against |
| 2.06 ms of GPU-busy time. Wall-clock around a python call measures dispatch, not the kernel. |
| |
| Rules enforced here: CUDA events (not time.time), warmup excluded, FRESH inputs per rep so a warm L2 |
| does not masquerade as bandwidth, min-of-N (not mean, which drifts with clocks), and an optional |
| GPU-busy cross-check so host-bound code is caught rather than reported as kernel time. |
| """ |
| import statistics |
| import torch |
|
|
|
|
| def bench(fn, make_args=None, args=None, reps=10, warmup=5, return_all=False): |
| """Time `fn`. Pass make_args(i)->tuple for fresh inputs per rep, or a fixed `args` tuple.""" |
| if make_args is None and args is None: |
| raise ValueError("pass make_args or args") |
| get = make_args if make_args is not None else (lambda i: args) |
|
|
| for i in range(warmup): |
| fn(*get(-1 - i)) |
| torch.cuda.synchronize() |
|
|
| times = [] |
| for i in range(reps): |
| a = get(i) |
| torch.cuda.synchronize() |
| s = torch.cuda.Event(enable_timing=True) |
| e = torch.cuda.Event(enable_timing=True) |
| s.record() |
| out = fn(*a) |
| e.record() |
| torch.cuda.synchronize() |
| times.append(s.elapsed_time(e) / 1e3) |
| del a, out |
| return (min(times), times) if return_all else min(times) |
|
|
|
|
| def gpu_busy(fn, args, reps=3): |
| """Sum of kernel time from the profiler. If this is far below `bench`, you are HOST-bound and the |
| kernel is not your problem yet -- go look at nsys, not ncu.""" |
| from torch.profiler import profile, ProfilerActivity |
| for _ in range(3): |
| fn(*args) |
| torch.cuda.synchronize() |
| with profile(activities=[ProfilerActivity.CUDA]) as p: |
| for _ in range(reps): |
| fn(*args) |
| torch.cuda.synchronize() |
| ks = [k for k in p.key_averages() if k.self_device_time_total > 0] |
| return sum(k.self_device_time_total for k in ks) / reps / 1e6, sum(k.count for k in ks) / reps |
|
|
|
|
| def report(fn, make_args=None, args=None, work=None, unit="TFLOP/s", **kw): |
| """Time, cross-check against GPU-busy, and convert to an achieved metric.""" |
| wall = bench(fn, make_args=make_args, args=args, **kw) |
| a = (make_args(0) if make_args else args) |
| busy, nk = gpu_busy(fn, a) |
| print(f"wall {wall*1e6:9.1f} us gpu-busy {busy*1e6:9.1f} us kernels/call {nk:.0f}") |
| if busy > 0 and wall / busy > 1.5: |
| print(f" !! wall is {wall/busy:.1f}x gpu-busy -- HOST-BOUND. Profile with nsys, not ncu.") |
| if work: |
| scale = 1e12 if unit == "TFLOP/s" else 2 ** 30 |
| print(f" achieved {work/wall/scale:.4g} {unit}") |
| return wall |
|
|
