Very slow between two operations
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Hello, in the processing stage, I use two operations. The first one : map + filter, is very fast and it uses the full cores, while the socond step is very slow and did not use full cores. 

Also, there is a significant lag between them.  Am I missing something ?



 ```
raw_datasets = raw_datasets.map(split_func, 
                batched=False,
                num_proc=args.preprocessing_num_workers,
                load_from_cache_file=not args.overwrite_cache, 
                desc = "running split para ==>")\
                .filter(lambda example: example['text1']!='' and example['text2']!='', 
                    num_proc=args.preprocessing_num_workers, desc="filtering ==>")


    processed_datasets = raw_datasets.map(
        preprocess_function,
        batched=True, 
        num_proc=args.preprocessing_num_workers,
        remove_columns=column_names,
        load_from_cache_file=not args.overwrite_cache,
        desc="Running tokenizer on dataset===>",
    )
```
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