My thirteenth week blog finished: The web version is here: https://adlternative.github.io/GSOC-Git-Blog-13/ ### Project Progress This week I continue to try to optimize the performance of `git cat-file --batch`. You can see them here: ```bash git fetch git@xxxxxxxxxx:adlternative/git.git cat-file-reuse-ref-filter-logic git rev-list 2c6ce95c82..8591897fbc ``` Or here: [[PATCH 00/27] [GSOC] [RFC] cat-file: reuse ref-filter logic](https://lore.kernel.org/git/pull.1016.git.1628842990.gitgitgadget@xxxxxxxxx/) Several of these commits are critical: * 31acac9fde `[GSOC] ref-filter: remove second parsing in format_ref_array_item`: It use a `parsed_atom_list` to save the parsed state after we calling verify_ref_format(), so we can reduce second parsing in format_ref_array_item(), which brings 1.9% performance improvement. * 4602b62a92 `[GSOC] ref-filter: reuse finnal buffer if no stack need`：It can reduce some unnecessary copies, which bring 2% performance improvement. This time I made sure that there was not too much noise, to ensure the stability of this performance test： #### Test Examples： * upstream/master: `5d213e46bb (tag: v2.33.0-rc2, upstream/master) Git 2.33-rc2` * 898e36a92b (before performance optimization): `898e36a92b [GSOC] cat-file: re-implement --textconv, --filters options` * this tree (after performance optimization): `8591897fbc (HEAD -> cat-file-reuse-ref-filter-logic) [GSOC] ref-filter: add need_get_object_info flag to struct expand_data` #### Test Results： ```bash $ GIT_PERF_REPEAT_COUNT=50 GIT_PERF_MAKE_OPTS=-j8 ./run upstream/master . ./p1006-cat-file.sh Test upstream/master this tree ------------------------------------------------------------------------------------ 1006.2: cat-file --batch-check 0.08(0.06+0.01) 0.08(0.07+0.01) +0.0% 1006.3: cat-file --batch-check with atoms 0.06(0.05+0.00) 0.07(0.06+0.01) +16.7% 1006.4: cat-file --batch 0.48(0.45+0.03) 0.50(0.46+0.03) +4.2% 1006.5: cat-file --batch with atoms 0.47(0.43+0.03) 0.49(0.46+0.02) +4.3% $ GIT_PERF_REPEAT_COUNT=50 GIT_PERF_MAKE_OPTS=-j8 ./run upstream/master 898e36a92b ./p1006-cat-file.sh Test upstream/master 898e36a92b ------------------------------------------------------------------------------------ 1006.2: cat-file --batch-check 0.08(0.07+0.00) 0.09(0.09+0.00) +12.5% 1006.3: cat-file --batch-check with atoms 0.06(0.04+0.01) 0.07(0.05+0.02) +16.7% 1006.4: cat-file --batch 0.48(0.44+0.03) 0.60(0.58+0.02) +25.0% 1006.5: cat-file --batch with atoms 0.47(0.44+0.02) 0.58(0.56+0.02) +23.4% ``` The performance of `git cat-file --batch-check` is very close to `upstream/master`! The performance difference of `git cat-file --batch` has also changed from 25.0% to 4.2%! This result is far better than my expectations, I have reason to believe that the performance of `git cat-file --batch` can be improved again! Good job! I think the key to continuing to optimize is still to reduce unnecessary copies. ### Additional advice During the optimization process this week, I found that I might want to use a `strbuf_move()` function, although I did not adopt it in my work (because it did not allow my work to be greatly optimized), but I think it might be useful in some situations: We don’t want to copy the data of strbuf, but just want to move its buf pointer: ```c void strbuf_move(struct strbuf *sb, struct strbuf *sb2) { strbuf_release(sb); *sb = *sb2; strbuf_init(sb2, 0); } ``` Yes, it's like `std::move()` in c++. [std::move](https://en.cppreference.com/w/cpp/utility/move) Maybe we can use strbuf_move() in some scenarios. Thanks, Git! -- ZheNing Hu
