Speedup model init on CPU (by 10x+ for llama-3-8B as one example) #31771
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The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. |
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Note: we're seeing some failures with encoder/decoder models that don't have tied weights. Not fully sure what's up there but @SunMarc is investigating |
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This can allegedly also increase throughput from Setup: import time
from accelerate.utils import set_seed
from transformers import LlamaForCausalLM, AutoTokenizer
set_seed(42)
file_size = 132 # Size in GB of the weights
factory_model = LlamaForCausalLM.from_pretrained("/mnt/superfast/llama-3-8B")
tokenizer = AutoTokenizer.from_pretrained("/mnt/superfast/llama-3-8B")
inputs = tokenizer("Blue is my favorite color. What is my favorite color?", return_tensors="pt")
start_time = time.time()
output = factory_model.generate(**inputs, max_new_tokens=20, num_return_sequences=1)
end_time = time.time()
time_taken = end_time - start_time
print(f"inference time={time_taken:.3f} seconds")
print(f"speed={file_size/time_taken:.3f} GB/second")
new_tokens = len(output[0]) - inputs.input_ids.shape[1]
print(f'tok/s={new_tokens/time_taken:.3f}')Current setup in HF: New version: |
muellerzr
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Did some tests with
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Wow - what an impactful PR 🔥 !
Only question is about deepspeed compatibility and compatibility across pytorch versions.
cc @gante for reference for the generate speedups
src/transformers/modeling_utils.py
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| if len(params_to_gather) > 0: | ||
| # because zero3 puts placeholders in model params, this context | ||
| # manager gathers (unpartitions) the params of the current layer, then loads from | ||
| # the state dict and then re-partitions them again | ||
| with deepspeed.zero.GatheredParameters(params_to_gather, modifier_rank=0): | ||
| if torch.distributed.get_rank() == 0: | ||
| module._load_from_state_dict(*args) |
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Have we tested the new code with deepspeed too?
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Not yet! To come next week :)
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I don't think this can work if the model has already been sharded under deepspeed ZeRO-3, because it hijacks the param tensors and the loading will ether fail (or worse silently remain random).
But I'd suggest to check in with the deepspeed team - perhaps they have some more recent tricks that will accomplish that faster.
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But in general - under zero.Init context the model is already spread out across the gpus, so you can't just overwrite its shards - w/o the machinery you propose to delete.
I think the just published Universal Checkpoint might be usable here to broadcast the updated tensor shards to each gpu, w/o needing to gather their content first.
@tjruwase, if possible could you please assist if there is a way to update the already sharded tensors in a faster way?
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of course if this doesn't work, then you'd need to have 2 code branches. The users who use zero.Init won't mind waiting, because the huge models they want to load won't load onto a single gpu, so cost of slower loading speed is a trade off here.
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@tjruwase, if possible could you please assist if there is a way to update the already sharded tensors in a faster way?
@stas00, I am just catching up on this, but my initial thought is wouldn't the following feature help for this case?
https://deepspeed.readthedocs.io/en/latest/zero3.html#modifying-partitioned-states
src/transformers/modeling_utils.py
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| if is_deepspeed_zero3_enabled(): | ||
| import deepspeed | ||
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| # In sharded models, each shard has only part of the full state_dict, so only gather | ||
| # parameters that are in the current state_dict. | ||
| named_parameters = dict(module.named_parameters(prefix=prefix[:-1], recurse=False)) | ||
| params_to_gather = [named_parameters[k] for k in state_dict.keys() if k in named_parameters] | ||
| if len(params_to_gather) > 0: | ||
| # because zero3 puts placeholders in model params, this context | ||
| # manager gathers (unpartitions) the params of the current layer, then loads from | ||
| # the state dict and then re-partitions them again | ||
| with deepspeed.zero.GatheredParameters(params_to_gather, modifier_rank=0): | ||
| if torch.distributed.get_rank() == 0: |
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I believe this should be as simple as migrating this chunk and having then the load_state_dict occur under this context manager.
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@msaroufim if you have a moment, could you give this a look to check that everything makes sense here per my understanding of how we should be loading in model weights, etc? Would be very appreciative of your eyes/take on this |
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For transparency, here is the script I'm using: https://gist.github.com/muellerzr/7239668f61baff5726f556d30d2af5f5 |
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💛 💛 💛 ( |
muellerzr
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Got confirmation from Mark S (thanks Mark for looking this over) and this is indeed correct 🔥 |
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A very important caveat @SunMarc and I discovered today: This works for now as a small fix to users who load everything on CPU instead first/don't do |
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About the failing tests, we had the following ones: it is a bit complicated but basically, these tests were not supposed to pass initially. However, they passed in the end because the weights were tied by default (even when For example, this is the architecture of def __init__(self, config, current_modality="text"):
super().__init__(config)
self.shared = nn.Embedding(config.vocab_size, config.hidden_size, config.pad_token_id)
self.text_encoder = SeamlessM4Tv2Encoder(config, self.shared)
self.speech_encoder = SeamlessM4Tv2SpeechEncoder(config)
self.text_decoder = SeamlessM4Tv2Decoder(config, self.shared)
self.lm_head = nn.Linear(config.hidden_size, config.vocab_size, bias=False)With this PR, we've set assign (bool, optional): When ``False``, the properties of the tensors
in the current module are preserved while when ``True``, the
properties of the Tensors in the state dict are preserved. The only
exception is the ``requires_grad`` field of :class:`~torch.nn.Parameter`s
for which the value from the module is preserved.
Default: ``False``So, the conclusion is that there should be no problem with the modification you did, I just need to skip/modify the tests. cc @muellerzr In the future, we just need to make sure that when we have shared weight by default, we skip the tests or add the possibility to remove these shared weights. |
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Okay ran some traces and I think this makes sense to me now. Compare the following first calls to Baseline:Fix: What this hints at here I believe is because we are using And because it's |
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@muellerzr, I am curious about the I/O speeds in your OP. Can you please confirm that you are transferring weights from NVMe to HBM at 75-90GB/sec? Are you able to share PCIe and m.2 specs? Thanks |
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@tjruwase the answer I've come to (as in my last post) is mmapping is covering the transition from m.2 when we first pass an input through the model (I think). Weights are only allocated in space, but not fully loaded in. Hence why I'm seeing far above what my actual M.2 drive can bring in, but at 8s of time to bring in said weights is reasonable if done quickly! (Because yes, I'd love to know what planet has a 75-90GB/s non-RAID M.2 as well!) My setup:
Let me know how much more specific I can get with this for you! |
@muellerzr, thanks for the clarification. As you may have guessed fast I/O is a passion, and I am also awaiting the above :). |
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@tjruwase do let me know if you see anything else odd about what I’ve done here etc too/if you have insights. I’ll look into the DeepSpeed stuff in a few days! |
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@muellerzr, your NVMe is blazingly fast, ~14GB/sec reads. May I request your contribution to the following? |
@muellerzr, nothing looks good. This is truly amazing work that you have done here, kudos! Do let me know if my suggestion for updating sharded DeepSpeed weights above is insufficient or problematic. |
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Okay! After a ton of thorough testing I've proven that:
Users will not see much speedup if they do |
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When I eventually ripped everything out to test, here's my full code: from transformers import LlamaForCausalLM, AutoConfig, AutoTokenizer
from accelerate.utils import set_seed
from accelerate.big_modeling import init_empty_weights
from safetensors.torch import load_file
from pathlib import Path
import json
from safetensors import safe_open
from accelerate.utils import retie_parameters
from transformers import GenerationConfig
from transformers.utils.hub import get_checkpoint_shard_files
import time
set_seed(42)
llama_path = Path("/mnt/superfast/llama-3-8B")
tokenizer = AutoTokenizer.from_pretrained(llama_path)
inputs = tokenizer("Tell me about a girl that", return_tensors="pt")
config = AutoConfig.from_pretrained(llama_path)
use_keep_in_fp32_modules = False
resolved_archive_file, sharded_metadata = get_checkpoint_shard_files(
llama_path,
llama_path/"model.safetensors.index.json"
)
loaded_state_dict_keys = sharded_metadata["all_checkpoint_keys"]
config = LlamaForCausalLM._autoset_attn_implementation(
config, use_flash_attention_2=False, torch_dtype=None, device_map=None
)
with init_empty_weights():
factory_model = LlamaForCausalLM(config)
index_filename = llama_path / "model.safetensors.index.json"
with open(index_filename, "r") as f:
index = json.load(f)
if "weight_map" in index:
index = index["weight_map"]
checkpoint_files = sorted(list(set(index.values())))
checkpoint_files = [llama_path / f for f in checkpoint_files]
model_keys = set(factory_model.state_dict().keys())
new_state_dict = {}
for checkpoint_file in checkpoint_files:
with safe_open(checkpoint_file, framework="pt") as f:
metadata = f.metadata()
weight_names = f.keys()
file_state = load_file(checkpoint_file)
new_state_dict.update(file_state)
factory_model.load_state_dict(new_state_dict, strict=True, assign=True)
retie_parameters(factory_model, [["lm_head.weight"]])
factory_model.eval()
factory_model.generation_config = GenerationConfig.from_pretrained(
llama_path
)
start_time = time.time()
output = factory_model.generate(**inputs, max_new_tokens=20, num_return_sequences=1)
end_time = time.time()
time_taken = end_time - start_time
new_tokens = len(output[0]) - inputs.input_ids.shape[1]
print(f"{time_taken:.3f}s | {new_tokens/time_taken:.3f} tokens/second | {tokenizer.batch_decode(output, skip_special_tokens=True)} | ") |
muellerzr
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@SunMarc @LysandreJik @ArthurZucker I've adjusted this title to what is really happening here. See the new updated table, basically we "borrow" a little time later on during the first pass to load the weights in, rather than doing so immediately which can load models in much faster and after the 1st pass will still be quick. On CUDA I saw nearly no time changes either, aside from loading the model in 0.185s rather than 2s for llama-3-8B, so that's safe too :) |
muellerzr
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muellerzr
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So that we can merge this, for now I've kept the old deepspeed behavior in |
Co-authored-by: Arthur <[email protected]>
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178 lines of diff --> 10x improvement in loading speed - what a ratio! 🔥🔥 🔥 🔥
Main comment is about having a _supports_assign_param_buffer attribute always set by default. Otherwise mostly nits.
The documentation should be updated to reflect the new logic. From a quick search, there's at least two place I saw to update, but there may be more:
- https://huggingface.co/docs/transformers/v4.42.0/en/main_classes/model#transformers.PreTrainedModel.from_pretrained.example
- - The from_pretrained docstring (for some reason the copy-link in the docs aren't working atm)
transformers/src/transformers/modeling_utils.py
Line 2953 in ac946aa
In the PR description - there's one bit I didn't understand in the First Pass section. What does "Afterwards they are ~ the same" mean?
src/transformers/modeling_utils.py
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| if start_prefix + first_key in state_dict: | ||
| return state_dict[start_prefix + first_key].dtype == model_to_load.state_dict()[first_key].dtype | ||
| else: | ||
| # For cases when the `state_dict` doesn't have any real weights (`albert`) |
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This is weird - what do we mean by "real weights" here? If I look at the safetensors file for a checkpoint it looks like there are weights
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It's in reference to test_model_weights_reload_no_missing_tied_weights, in which case we have nuked the saved tensors and as a result they don't exist in the state dict at all etc. In this case we should return False. I've changed it to reference the specific test.
(In most real world cases, we shouldn't get to this point)
Co-authored-by: amyeroberts <[email protected]>
…ingface/transformers into muellerzr-speedup-inference
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@amyeroberts reworked the PR description, let me know if everything makes sense now 🤗 |
| @@ -894,32 +895,42 @@ def test_from_pretrained_low_cpu_mem_usage_functional(self): | |||
| @require_usr_bin_time | |||
| @require_accelerate | |||
| @mark.accelerate_tests | |||
| def test_from_pretrained_low_cpu_mem_usage_measured(self): | |||
| # test that `from_pretrained(..., low_cpu_mem_usage=True)` uses less cpu memory than default | |||
| def test_from_pretrained_low_cpu_mem_usage_slower(self): | |||
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Shouldn't it be faster?
| def test_from_pretrained_low_cpu_mem_usage_slower(self): | |
| def test_from_pretrained_low_cpu_mem_usage_faster(self): |
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Was running the tests, it's a bit slower due to the added hooks IMO (which is fine, as low_cpu_mem_usage=True is still needed 99% of the time, aka when weights != precision)
What does this PR do?
This PR introduces utilizing
_assign_to_params_buffersas a way to speed up weight loading if the dtypes of models are the same. By doing so, we can lazily load in model weights on the fly when an input is passed in, decreasing the TTL of both training and inference wrt the speed of your disk.The benefit of this is now
low_cpu_mem_usageand this have ~ the same memory usage if and only if the model weights precision == the loaded model precision.For example, this will only work if you load in
llama-3-8Binbfloat16, since the weights and architecture are both inbfloat16.Unsupported models
Some models also do not support buffer param assignments. I've added a new
_supports_param_buffer_assignmentattr to the specific models that do not, while eventually it'd be good to investigate this if any models fail thetest_from_pretrained_no_checkpointtests, they need to set this attribute in their model config (similar to howVisionEncoderDecoderModelhassupports_gradient_checkpointing=False).Example model init time:
Example model throughput:
First pass
Afterwards both lazy-loaded and non-lazy loaded inference times are the same (since we no longer need to read the weights in)
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@LysandreJik @amyeroberts @SunMarc