Re: [PATCH 07/10] perf jevents: Add --compress=zstd block compression backend

[sashiko-bot@kernel.org]

> Add a 'zstd' block-indexed string compression backend to jevents.py that
> trains a single shared 64 KiB Zstandard dictionary across all ~8 KiB
> string blocks (itself stored zstd-compressed in .rodata and digested
> once on demand into a shared ZSTD_DDict freed at exit) and compresses
> each ~8 KiB block independently with ZSTD_compress_usingCDict().
> 
> Without a dictionary, each ~8 KiB block starts with an empty match
> window and must emit its own Huffman/FSE entropy tables from scratch.
> Sharing a trained 64 KiB dictionary pre-seeds both common event/metric
> substrings and precomputed entropy tables across all blocks, shrinking
> compressed .rodata by ~26% compared to dictionary-free ~8 KiB zstd
> blocks (738 KiB vs 1,003 KiB across all architectures, recovering over
> half the gap toward a single non-seekable 521 KiB whole-table stream)
> while keeping every block independently decompressible via
> (block_id << 16) | sub_offset.
> 
> To avoid mandatory third-party Python package dependencies across Python
> versions, lazily probe three Zstandard bindings in order:
>   1. Python 3.14+ standard-library compression.zstd
>   2. python-zstandard (zstandard) if installed
>   3. ctypes binding to the system libzstd shared library
> 
> When total string data is too small to train a dictionary, gracefully
> fall back to dictionary-free Zstandard frames. On x86, --compress=zstd
> shrinks pmu-events-string.o from ~6.90 MB to ~587 KB (~11.8x reduction).
> 
> Signed-off-by: Ian Rogers <irogers@google.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261113210822.3112700-1-irogers@google.com?part=7