feat: add easycache support

[rmatif]

This PR adds support for Easycache, a variant of TeaCache that achieves significant speedup

Currently tested only with CUDA and on Flux/Qwen

Command usage:

--easycache threshold,start_percent,end_percent

Examples:

Without Easycache	--easycache 0.2,0.15,0.95	Speedup
		x1.85
		x1.85

[Green-Sky]

Ran it with a SPARK (preview) Chroma finetune

thresh	img	real speedup
0		baseline
0.025		1.12x
0.1		1.31x
0.2		1.4x

I noticed the estimated speedup is off. It is off exactly by 2x, so I guess cfg is not handled properly yet.

eg. 40steps with cfg are actually 80 steps

40/(40-8) -> 1.25 (estimated 1.25)
80/(80-8) -> 1.11 (measured 1.12)

I included 0.025, because that is what the original used for wan.

Anyway Good stuff, I take the 11% speedup.

$ result/bin/sd --diffusion-model models/SPARK.Chroma_preview-q5_k.gguf --t5xxl models/flux-extra/t5xxl_fp16.safetensors -t 8 --vae models/flux-extra/ae-f16.gguf --sampling-method dpm++2m --scheduler simple --steps 40 --cfg-scale 3.8 -n "low quality, ugly, unfinished, out of focus, deformed, disfigure, blurry, smudged, restricted palette, flat colors, noisy, artifacts, fake, generated, overblown, over exposed" -p "Photograph of a lovely cat. Green rolling hills in the background." --clip-on-cpu --offload-to-cpu -v -W 768 -H 1024 --diffusion-fa --chroma-disable-dit-mask --easycache 0.025,0.15,0.95

[JohnLoveJoy]

Ran it with a SPARK (preview) Chroma finetune

thresh img real speedup
0 baseline
0.025 1.12x
0.1 1.31x
0.2 1.4x
I noticed the estimated speedup is off. It is off exactly by 2x, so I guess cfg is not handled properly yet.

eg. 40steps with cfg are actually 80 steps

40/(40-8) -> 1.25 (estimated 1.25)
80/(80-8) -> 1.11 (measured 1.12)

I included 0.025, because that is what the original used for wan.

Anyway Good stuff, I take the 11% speedup.

$ result/bin/sd --diffusion-model models/SPARK.Chroma_preview-q5_k.gguf --t5xxl models/flux-extra/t5xxl_fp16.safetensors -t 8 --vae models/flux-extra/ae-f16.gguf --sampling-method dpm++2m --scheduler simple --steps 40 --cfg-scale 3.8 -n "low quality, ugly, unfinished, out of focus, deformed, disfigure, blurry, smudged, restricted palette, flat colors, noisy, artifacts, fake, generated, overblown, over exposed" -p "Photograph of a lovely cat. Green rolling hills in the background." --clip-on-cpu --offload-to-cpu -v -W 768 -H 1024 --diffusion-fa --chroma-disable-dit-mask --easycache 0.025,0.15,0.95

Is this additional noise in the image expected? I haven’t noticed it in other Tea Cache tests or similar methods.

[Green-Sky]

Is this additional noise in the image expected? I haven’t noticed it in other Tea Cache tests or similar methods.

I speculate that this happens with some models (see second pic OP) when too much is skipped at the end of the sampling phase. You can lower the second value from 0.95 to 0.80 or lower. This will result in less skips late, but also less skips overall, so it is not conclusive(!).

I observed similar behavoir with beta/smoothstep schedulers, which reduce the noise in those models. The scheduler spends more time in early and late timesteps of the sampling (s-cuve or gain function behavoir).

edit: Ofc this pr can be broken too. Also other factors is the quant used, which seems to exacerbate the noise.

edit2: Here is what smoothstep(almost beta) with 20 steps looks like:

[Green-Sky]

I think it would be simpler if --easycache threshold,start_percent,end_percent is split into 3 or 4 commands. You generally just want to enable the safe default OR only modify threshold.
Or maybe make star and end optional? Not sure.