Following up on a discussion [1] around cache tree refreshes in 'git reset',
this series updates callers of 'unpack_trees()' to skip its internal
invocation of 'cache_tree_update()' when 'prime_cache_tree()' is called
immediately after 'unpack_trees()'. 'cache_tree_update()' can be an
expensive operation, and it is redundant when 'prime_cache_tree()' clears
and rebuilds the cache tree from scratch immediately after.
The first patch adds a test directly comparing the execution time of
'prime_cache_tree()' with that of 'cache_tree_update()'. The results show
that on a fully-valid cache tree, they perform the same, but on a partially-
or fully-invalid cache tree (the more likely case in commands with the
aforementioned redundancy), 'prime_cache_tree()' is faster.
The second patch introduces the 'skip_cache_tree_update' option for
'unpack_trees()', but does not use it yet.
The remaining three patches update callers that make the aforementioned
redundant cache tree updates. The performance impact on these callers ranges
from "negligible" (in 'rebase') to "substantial" (in 'read-tree') - more
details can be found in the commit messages of the patch associated with the
affected code path.
Changes since V2
================
* Cleaned up option handling & provided more informative error messages in
'test-tool cache-tree'. The changes don't affect any behavior in the
added tests & 'test-tool cache-tree' won't be used outside of
development, but the improvements here will help future readers avoid
propagating error-prone implementations.
* Note that the suggestion to change the "unknown subcommand" error to a
'usage()' error was not taken, as it would be somewhat cumbersome to
use a formatted string with it. This is in line with other custom
subcommand parsing in Git, such as in 'fsmonitor--daemon.c'.
Changes since V1
================
* Rewrote 'p0090' to more accurately and reliably test 'prime_cache_tree()'
vs. 'cache_tree_update()'.
* Moved iterative cache tree update out of C and into the shell tests (to
avoid potential runtime optimizations)
* Added a "control" test to document how much of the execution time is
startup overhead
* Added tests demonstrating performance in partially-invalid cache trees.
* Fixed the use of 'prime_cache_tree()' in 'test-tool cache-tree', changing
it from using the tree at HEAD to the current cache tree.
Thanks!
* Victoria
[1] https://lore.kernel.org/git/xmqqlf30edvf.fsf@gitster.g/ [2]
https://lore.kernel.org/git/f4881b7455b9d33c8a53a91eda7fbdfc5d11382c.1627066238.git.jonathantanmy@xxxxxxxxxx/
Victoria Dye (5):
cache-tree: add perf test comparing update and prime
unpack-trees: add 'skip_cache_tree_update' option
reset: use 'skip_cache_tree_update' option
read-tree: use 'skip_cache_tree_update' option
rebase: use 'skip_cache_tree_update' option
Makefile | 1 +
builtin/read-tree.c | 4 ++
builtin/reset.c | 2 +
reset.c | 1 +
sequencer.c | 1 +
t/helper/test-cache-tree.c | 64 ++++++++++++++++++++++++++++++
t/helper/test-tool.c | 1 +
t/helper/test-tool.h | 1 +
t/perf/p0006-read-tree-checkout.sh | 8 ++++
t/perf/p0090-cache-tree.sh | 36 +++++++++++++++++
t/perf/p7102-reset.sh | 21 ++++++++++
t/t1022-read-tree-partial-clone.sh | 2 +-
unpack-trees.c | 3 +-
unpack-trees.h | 3 +-
14 files changed, 145 insertions(+), 3 deletions(-)
create mode 100644 t/helper/test-cache-tree.c
create mode 100755 t/perf/p0090-cache-tree.sh
create mode 100755 t/perf/p7102-reset.sh
base-commit: 3b08839926fcc7cc48cf4c759737c1a71af430c1
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1411%2Fvdye%2Ffeature%2Fcache-tree-optimization-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1411/vdye/feature/cache-tree-optimization-v3
Pull-Request: https://github.com/gitgitgadget/git/pull/1411
Range-diff vs v2:
1: 833519d87c8 ! 1: 2b48a684156 cache-tree: add perf test comparing update and prime
@@ Commit message
partially invalid (e.g., 'git reset --hard'), 'prime_cache_tree()' will
likely perform better than 'cache_tree_update()' in typical cases.
+ Helped-by: SZEDER Gábor <szeder.dev@xxxxxxxxx>
Signed-off-by: Victoria Dye <vdye@xxxxxxxxxx>
## Makefile ##
@@ t/helper/test-cache-tree.c (new)
+
+ setup_git_directory();
+
-+ parse_options(argc, argv, NULL, options, test_cache_tree_usage, 0);
++ argc = parse_options(argc, argv, NULL, options, test_cache_tree_usage, 0);
+
+ if (read_cache() < 0)
-+ die("unable to read index file");
++ die(_("unable to read index file"));
+
+ oidcpy(&oid, &the_index.cache_tree->oid);
+ tree = parse_tree_indirect(&oid);
@@ t/helper/test-cache-tree.c (new)
+ cache_tree_invalidate_path(&the_index, the_index.cache[i * interval]->name);
+ }
+
-+ if (!argc)
-+ die("Must specify subcommand");
++ if (argc != 1)
++ usage_with_options(test_cache_tree_usage, options);
+ else if (!strcmp(argv[0], "prime"))
+ prime_cache_tree(the_repository, &the_index, tree);
+ else if (!strcmp(argv[0], "update"))
+ cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
+ /* use "control" subcommand to specify no-op */
+ else if (!!strcmp(argv[0], "control"))
-+ die("Unknown command %s", argv[0]);
++ die(_("Unhandled subcommand '%s'"), argv[0]);
+
+ return 0;
+}
2: b015a4f531c = 2: 0e03614f0fd unpack-trees: add 'skip_cache_tree_update' option
3: 4f6039971b8 = 3: 386f18ca36a reset: use 'skip_cache_tree_update' option
4: 5a646bc47c9 = 4: ea5c82ce992 read-tree: use 'skip_cache_tree_update' option
5: fffe2fc17ed = 5: 100c01e936c rebase: use 'skip_cache_tree_update' option
--
gitgitgadget
