xformers produces result deviation ?

[dynatron832]

hi
i dont know if this a bug or simply normal with the xformers optimization.

if i start webui without the --xformers option enter prompt ...setting (or simply transfer all settings from a previous file via PNG info) ...fixed seed and so on ....SD is producing over and over the same pic. no matter how many pictures.
but
if i start SDwebui with the --xformers option and render the same prompt´s/seed ...the result is very visible a deviation from the one without the xformers option active. yes the picture generation is faster. but the result´s are not the same as they should be. and dont get me wrong. it´s not the result is a totaly other result. no ...it is the prompt+seed. but there are deviations ...light reflection, colors, shapes, they're small but very visible if you compare the picture. and they're everytime different. on every picture. allmost as if the seed variation is activated. but it isn't. it's of. and if i start SD without xformers the matching result to seed/prompt is back.

is this normal ? is this intendend ? is there some option to prevent SD image's that deviate from each other ? or is it some bug ?

[ghost]

It's normal xformers behaviour. You get optimisation, you lose complete repeatability.

[dynatron832]

is there some way to in/decrease this behavior of xformers ?

[ghost]

No.

[fractal-fumbler]

@dynatron832, try --xformers-flash-attention for enable xformers with Flash Attention to improve reproducibility

p.s. supported for SD2.x checkpoints only)

[dynatron832]

it look´s like SD isn't loading the xformers with the argument. on the webui he say's xformers: N/A
if i start with the regular --xformers then he show xformers: 0.0.16rc425