block wise quantization support

[ved1beta]

SUMMARY:
added support for blcok wise quant changes in def calculate_qparams

def calculate_qparams(
       self,
       observed: Tensor,
       reduce_dims: Optional[Tuple[int]] = None,
       tensor_id: Optional[Any] = None,
       global_scale: Optional[Tensor] = None,
   ) -> Tuple[FloatTensor, IntTensor]: 

fixes #1475

TEST PLAN:
this is repro script from the issue passes

from llmcompressor import oneshot
from llmcompressor.modifiers.quantization import QuantizationModifier
form transformers import AutoModelForCausalLM
from compressed_tensors.quantization import (
    QuantizationArgs,
    QuantizationConfig,
    QuantizationScheme,
    QuantizationStrategy,
    QuantizationType,
)

MODEL_ID = "meta-llama/Llama-3.2-3B-Instruct"

# define a llmcompressor recipe for FP8 W8A8 quantization
# since the MoE gate layers are sensitive to quantization, we add them to the ignore
# list so they remain at full precision
recipe = [
    QuantizationModifier(
        ignore=["lm_head", "re:.*mlp.gate$"],
        config_groups={
            "group_0": QuantizationScheme(
                targets=["Linear"],
                weights=QuantizationArgs(
                    num_bits=4,
                    type=QuantizationType.INT,
                    dynamic=False,
                    symmetric=False,
                    strategy=QuantizationStrategy.BLOCK,
                    # group_size=128,
                    block_structure="128x128",
                ),
            )
        },
    )
]

SAVE_DIR = MODEL_ID + "-W4A16-BLOCK128"

model = AutoModelForCausalLM.from_pretrained(
    MODEL_ID, device_map="auto", torch_dtype="bfloat16", trust_remote_code=True
)


oneshot(
    model=model,
    recipe=recipe,
    save_compressed=True,
    output_dir=SAVE_DIR,
)

EDIT:
ERROR: RuntimeError: output with shape [1] doesn't match the broadcast shape [512, 8]

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[brian-dellabetta]

Thanks for taking a look! Left a few comments. it would also be good to make sure block-wise quantization can run on vllm, beyond just making sure the script runs. Apparently some of this is set up in vllm already -- #1475 (comment)

[brian-dellabetta]

I think the majority of your logic you'll want to have in here, or in a helper method that this calls to help with readability.

[brian-dellabetta]

these should have shape (rows, num_blocks), similar to how group-wise is set up here

[dsikka]

Generally speaking, all quantization types and their applications should live in compressed tensors

[shuxiaobo]

@dsikka @brian-dellabetta Is there any progress?

[ved1beta]

so i tried moving all the code to get_params then got a shape mismatch issue .The implementation has shape mismatches that cause runtime errors when trying to update quantization parameters.
The main error is: output with shape [1] doesn't match the broadcast shape [512, 8] or [768, 6]. This happens because a scalar parameter is being used where a 2D tensor with specific dimensions is expected.
Should i push the changes for you guys to have a look ? i am not sure what todo next

[brian-dellabetta]

Hi @ved1beta , thanks for the update, feel free to push the changes. This is a more difficult issue than most of our "good first issue"s. I can take a look when i have some down time.

Hi @shuxiaobo , this is lower priority given the other work going on in llm-compressor, so might take some time. And we'll have to figure out which configurations are optimized to work well in vllm. Consider using group instead of block for your runs, which has good support already.

[brian-dellabetta]

Hi @ved1beta , I am going to close this in favor of the PRs to support block-wise quantization from one of the vllm maintainers. You can see how functionality was added in these PRs:

• Support DeepSeekV3-style block FP8 quantization #1607
• Support DeepSeekV3-style block FP8 quantization compressed-tensors#372
• Support DeepSeekV3-style block FP8 quantization with CT vllm#20279

We appreciate you taking an initial stab at this though. The implementation here is the meat of adding it to llmcompressor, but as you can see from the PRs there are a lot of other things to consider. We're still trying to figure out how best to label good first issues and encourage community involvement