From 8922c21c9e4c98e054973fa8c0fb629a3cd579c3 Mon Sep 17 00:00:00 2001 From: Rattus Date: Tue, 16 Sep 2025 20:33:23 +1000 Subject: [PATCH] flux: Do the xq and xk ropes one at a time This was doing independendent interleaved tensor math on the q and k tensors, leading to the holding of more than the minimum intermediates in VRAM. On a bad day, it would VRAM OOM on xk intermediates. Do everything q and then everything k, so torch can garbage collect all of qs intermediates before k allocates its intermediates. This reduces peak VRAM usage for some WAN2.2 inferences (at least). --- comfy/ldm/flux/math.py | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff --git a/comfy/ldm/flux/math.py b/comfy/ldm/flux/math.py index 4d743cda2..fb7cd7586 100644 --- a/comfy/ldm/flux/math.py +++ b/comfy/ldm/flux/math.py @@ -35,11 +35,10 @@ def rope(pos: Tensor, dim: int, theta: int) -> Tensor: out = rearrange(out, "b n d (i j) -> b n d i j", i=2, j=2) return out.to(dtype=torch.float32, device=pos.device) +def apply_rope1(x: Tensor, freqs_cis: Tensor): + x_ = x.to(dtype=freqs_cis.dtype).reshape(*x.shape[:-1], -1, 1, 2) + x_out = freqs_cis[..., 0] * x_[..., 0] + freqs_cis[..., 1] * x_[..., 1] + return x_out.reshape(*x.shape).type_as(x) def apply_rope(xq: Tensor, xk: Tensor, freqs_cis: Tensor): - xq_ = xq.to(dtype=freqs_cis.dtype).reshape(*xq.shape[:-1], -1, 1, 2) - xk_ = xk.to(dtype=freqs_cis.dtype).reshape(*xk.shape[:-1], -1, 1, 2) - xq_out = freqs_cis[..., 0] * xq_[..., 0] + freqs_cis[..., 1] * xq_[..., 1] - xk_out = freqs_cis[..., 0] * xk_[..., 0] + freqs_cis[..., 1] * xk_[..., 1] - return xq_out.reshape(*xq.shape).type_as(xq), xk_out.reshape(*xk.shape).type_as(xk) - + return apply_rope1(xq, freqs_cis), apply_rope1(xk, freqs_cis)