Fix: Clean up examples and unify request read signature #17
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Summary of Changes
Hello @haochengxia, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request primarily focuses on refining the libCacheSim Python binding's API for reading requests and overhauling its example documentation. The core change unifies the read_one_req signature across different reader types, making the API more consistent and user-friendly. Concurrently, a significant cleanup of the example directory and the README.md file has been performed to provide clearer, more up-to-date usage examples and remove outdated content.
Highlights
- API Unification for Request Reading: The
read_one_reqmethod acrossSyntheticReaderandTraceReaderhas been updated to return aRequestobject directly, simplifying its usage by removing the need to pre-allocate and pass aRequestobject. - Comprehensive Example Overhaul: The entire
examples/directory has been restructured and cleaned up. Outdated and redundant example scripts have been removed, and new, concise examples (basic_usage.py,plugin_cache/s3fifo.py) have been added to demonstrate core functionalities like trace processing and custom cache policy implementation. - README.md Modernization: The main
README.mdhas been significantly updated to reflect the new API and examples. Obsolete sections (Documentation links, Features, Old Examples, Troubleshooting) have been removed, and new sections for trace processing withDataLoaderand a detailedPluginCacheexample have been introduced. - Improved PluginCache Hook Signatures: The
PluginCachehook functions (hit_hook,miss_hook,eviction_hook) now receive aRequestobject directly, providing more comprehensive information about the current request within the custom policy logic.
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Code Review
This pull request cleans up the examples and unifies the request reader signature across the library, which is a great simplification of the API. The changes involve removing old examples, adding new ones that reflect current best practices, and updating the README.
My review has identified a few issues:
- A critical bug in
TraceReader.__getitem__and__next__where it returns an incorrect type. - Several high-severity issues in the new examples, including incorrect cache size configurations for comparisons and logical errors in implementation that could lead to incorrect behavior or crashes.
- Some medium-severity issues in the README regarding clarity and typos, and a recommendation to add a test case for the
__getitem__functionality to prevent future regressions.
| def __getitem__(self, index: int) -> Request: | ||
| if index < 0 or index >= self._reader.get_num_of_req(): | ||
| raise IndexError("Index out of range") | ||
| self._reader.reset() | ||
| self._reader.skip_n_req(index) | ||
| return self._reader.read_one_req() | ||
| req = Request() | ||
| return self._reader.read_one_req(req) |
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The __getitem__ method is implemented to return self._reader.read_one_req(req). Due to the changes in the C++ bindings, this call now returns an integer status code, not the Request object. This means __getitem__ will incorrectly return an integer instead of a Request instance, which violates its type hint and will break any code that uses it.
The req object is populated by reference, so you should return req after the call to _reader.read_one_req(req).
| def __getitem__(self, index: int) -> Request: | |
| if index < 0 or index >= self._reader.get_num_of_req(): | |
| raise IndexError("Index out of range") | |
| self._reader.reset() | |
| self._reader.skip_n_req(index) | |
| return self._reader.read_one_req() | |
| req = Request() | |
| return self._reader.read_one_req(req) | |
| def __getitem__(self, index: int) -> Request: | |
| if index < 0 or index >= self._reader.get_num_of_req(): | |
| raise IndexError("Index out of range") | |
| self._reader.reset() | |
| self._reader.skip_n_req(index) | |
| req = Request() | |
| self._reader.read_one_req(req) | |
| return req |
| cache = lcs.S3FIFO(cache_size=1024*1024) | ||
| obj_miss_ratio, byte_miss_ratio = cache.process_trace( | ||
| reader, | ||
| start_req=0, | ||
| max_req=1000 | ||
| ) | ||
| print(f"Object miss ratio: {obj_miss_ratio:.4f}, Byte miss ratio: {byte_miss_ratio:.4f}") No newline at end of file |
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The reader object is being reused for a second process_trace call without being reset. After the first call, the reader's internal cursor will be at the end of the trace, so the second call will process zero requests, leading to misleading results.
You should call reader.reset() before reusing it to ensure the trace is read from the beginning.
| cache = lcs.S3FIFO(cache_size=1024*1024) | |
| obj_miss_ratio, byte_miss_ratio = cache.process_trace( | |
| reader, | |
| start_req=0, | |
| max_req=1000 | |
| ) | |
| print(f"Object miss ratio: {obj_miss_ratio:.4f}, Byte miss ratio: {byte_miss_ratio:.4f}") | |
| cache = lcs.S3FIFO(cache_size=1024*1024) | |
| reader.reset() | |
| obj_miss_ratio, byte_miss_ratio = cache.process_trace( | |
| reader, | |
| start_req=0, | |
| max_req=1000 | |
| ) | |
| print(f"Object miss ratio: {obj_miss_ratio:.4f}, Byte miss ratio: {byte_miss_ratio:.4f}") |
examples/plugin_cache/s3fifo.py
Outdated
| def cache_eviction_hook(cache, request: Request): | ||
| # NOTE(haocheng): never called | ||
| pass |
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The cache_eviction_hook is implemented as a no-op (pass). According to the README.md, this hook should return the object ID to evict. A pass statement will cause the function to return None, which will likely cause a runtime error in the C++ backend that expects an integer object ID.
The StandaloneS3FIFO class has a cache_evict method that seems to implement the correct eviction logic. This hook should probably call it.
| def cache_eviction_hook(cache, request: Request): | |
| # NOTE(haocheng): never called | |
| pass | |
| def cache_eviction_hook(cache, request: Request): | |
| return cache.cache_evict() |
examples/plugin_cache/s3fifo.py
Outdated
| cache_free_hook=cache_free_hook, | ||
| cache_name="S3FIFO") | ||
|
|
||
| ref_s3fifo = S3FIFO(cache_size=1024) |
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The reference S3FIFO cache is initialized with a size of 1024, while the plugin cache under test is initialized with 1024*1024. For the comparison to be valid and for the assertion plugin_hit == ref_hit to work correctly, both caches should have the same size.
| ref_s3fifo = S3FIFO(cache_size=1024) | |
| ref_s3fifo = S3FIFO(cache_size=1024*1024) |
| ``` | ||
|
|
||
| > [!NOTE] | ||
| > We DO NOT ignore the object size by defaults, you can add `reader_init_params = lcs.ReaderInitParam(ignore_obj_size=False)` to the initialization of `TraceReader` if needed. |
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The note about ignore_obj_size is a bit confusing. It states that the default is not to ignore object size (i.e., ignore_obj_size=False), and then suggests adding reader_init_params = lcs.ReaderInitParam(ignore_obj_size=False) if needed, which is redundant.
A clearer explanation would be more helpful for users, for instance, explaining when they might want to set it to True.
| > We DO NOT ignore the object size by defaults, you can add `reader_init_params = lcs.ReaderInitParam(ignore_obj_size=False)` to the initialization of `TraceReader` if needed. | |
| To ignore object sizes, add `reader_init_params = lcs.ReaderInitParam(ignore_obj_size=True)` to the `TraceReader` initialization. This can improve performance when object sizes are irrelevant. |
README.md
Outdated
| - Educational purposes and learning | ||
| - Research and experimentation | ||
| - Custom business logic implementation | ||
| The `PluginCache` allows you to define custom caching behavior through Python callback functions without without any C/C++ compilation. |
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There is a typo here: "without without".
| The `PluginCache` allows you to define custom caching behavior through Python callback functions without without any C/C++ compilation. | |
| The `PluginCache` allows you to define custom caching behavior through Python callback functions without any C/C++ compilation. |
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