This series depends on en/ort-perf-batch-11 textually, but is semantically
independent of it.
Changes since v1 (all for the first patch):
* Add more comments explaining the sorting function, its purpose, and how
its expected to be called
* Small style fixup
* Switch back to using string_list_sort() instead of direct QSORT()
This short series has a few optimizations, but only one of which affects the
testcases of interest (namely, reducing our time spent on sorting an array).
It also fixes a few comments.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28), the
changes in just this series improves the performance as follows:
Before Series After Series
no-renames: 5.622 s ± 0.059 s 5.235 s ± 0.042 s
mega-renames: 10.127 s ± 0.073 s 9.419 s ± 0.107 s
just-one-mega: 500.3 ms ± 3.8 ms 480.1 ms ± 3.9 ms
As a reminder, before any merge-ort/diffcore-rename performance work, the
performance results we started with were:
no-renames-am: 6.940 s ± 0.485 s
no-renames: 18.912 s ± 0.174 s
mega-renames: 5964.031 s ± 10.459 s
just-one-mega: 149.583 s ± 0.751 s
Elijah Newren (5):
merge-ort: replace string_list_df_name_compare with faster alternative
diffcore-rename: avoid unnecessary strdup'ing in break_idx
diffcore-rename: enable limiting rename detection to relevant
destinations
Fix various issues found in comments
merge-ort: miscellaneous touch-ups
diffcore-rename.c | 52 ++++++++++++++---
diffcore.h | 2 +
merge-ort.c | 86 +++++++++++++++++++++--------
t/t6423-merge-rename-directories.sh | 2 +-
4 files changed, 110 insertions(+), 32 deletions(-)
base-commit: 76e253793c9a1d7fdd1836d5e4db26dabd3d713a
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-962%2Fnewren%2Fort-perf-batch-12-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-962/newren/ort-perf-batch-12-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/962
Range-diff vs v1:
1: 5055dfce3281 ! 1: c4a0f6a9510c merge-ort: replace string_list_df_name_compare with faster alternative
@@ Commit message
"-sort" to either rebase or merge, sorting an array takes more time than
anything else. Serves me right for naming my merge strategy this way.
- Rewrite the comparison function and remove as many levels of indirection
- as possible (e.g. the old code had
- cmp_items() ->
- string_list_df_name_compare() ->
- df_name_compare()
- now we just have sort_dirs_next_to_their_children()), and tweak it to be
- as optimized as possible for our specific case. These changes reduced
- the time spent in "plist special sort" by ~25% in the mega-renames case.
+ Rewrite the comparison function in a way that does not require finding
+ out the lengths of the strings when comparing them. While at it, tweak
+ the code for our specific case -- no need to handle a variety of modes,
+ for example. The combination of these changes reduced the time spent in
+ "plist special sort" by ~25% in the mega-renames case.
For the testcases mentioned in commit 557ac0350d ("merge-ort: begin
performance work; instrument with trace2_region_* calls", 2020-10-28),
@@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
/*** Function Grouping: functions related to process_entries() ***/
-static int string_list_df_name_compare(const char *one, const char *two)
-+static int sort_dirs_next_to_their_children(const void *a, const void *b)
++static int sort_dirs_next_to_their_children(const char *one, const char *two)
{
- int onelen = strlen(one);
- int twolen = strlen(two);
++ unsigned char c1, c2;
++
/*
- * Here we only care that entries for D/F conflicts are
- * adjacent, in particular with the file of the D/F conflict
- * appearing before files below the corresponding directory.
- * The order of the rest of the list is irrelevant for us.
+ * Here we only care that entries for directories appear adjacent
-+ * to and before files underneath the directory. In other words,
-+ * we do not want the natural sorting of
++ * to and before files underneath the directory. We can achieve
++ * that by pretending to add a trailing slash to every file and
++ * then sorting. In other words, we do not want the natural
++ * sorting of
+ * foo
+ * foo.txt
+ * foo/bar
@@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
+ * To achieve this, we basically implement our own strcmp, except that
+ * if we get to the end of either string instead of comparing NUL to
+ * another character, we compare '/' to it.
++ *
++ * If this unusual "sort as though '/' were appended" perplexes
++ * you, perhaps it will help to note that this is not the final
++ * sort. write_tree() will sort again without the trailing slash
++ * magic, but just on paths immediately under a given tree.
*
- * To achieve this, we sort with df_name_compare and provide
- * the mode S_IFDIR so that D/F conflicts will sort correctly.
@@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
- * since in other cases any changes in their order due to
- * sorting cause no problems for us.
+ * The reason to not use df_name_compare directly was that it was
-+ * just too expensive, so I had to reimplement it.
++ * just too expensive (we don't have the string lengths handy), so
++ * I had to reimplement it.
*/
- int cmp = df_name_compare(one, onelen, S_IFDIR,
- two, twolen, S_IFDIR);
-- /*
++
+ /*
- * Now that 'foo' and 'foo/bar' compare equal, we have to make sure
- * that 'foo' comes before 'foo/bar'.
-- */
++ * NOTE: This function will never be called with two equal strings,
++ * because it is used to sort the keys of a strmap, and strmaps have
++ * unique keys by construction. That simplifies our c1==c2 handling
++ * below.
+ */
- if (cmp)
- return cmp;
- return onelen - twolen;
-+ const char *one = ((struct string_list_item *)a)->string;
-+ const char *two = ((struct string_list_item *)b)->string;
-+ unsigned char c1, c2;
+
+ while (*one && (*one == *two)) {
+ one++;
@@ merge-ort.c: static int detect_and_process_renames(struct merge_options *opt,
+ if (c1 == c2) {
+ /* Getting here means one is a leading directory of the other */
+ return (*one) ? 1 : -1;
-+ }
-+ else
++ } else
+ return c1-c2;
}
@@ merge-ort.c: static void process_entries(struct merge_options *opt,
trace2_region_enter("merge", "plist special sort", opt->repo);
- plist.cmp = string_list_df_name_compare;
-- string_list_sort(&plist);
-+ QSORT(plist.items, plist.nr, sort_dirs_next_to_their_children);
++ plist.cmp = sort_dirs_next_to_their_children;
+ string_list_sort(&plist);
trace2_region_leave("merge", "plist special sort", opt->repo);
- trace2_region_leave("merge", "process_entries setup", opt->repo);
2: 7212816c8d47 = 2: 38713ed48273 diffcore-rename: avoid unnecessary strdup'ing in break_idx
3: 19150b575058 = 3: 45e1de5fe780 diffcore-rename: enable limiting rename detection to relevant destinations
4: 98c9a419b313 = 4: 2f26d7e935c0 Fix various issues found in comments
5: e85dad887f95 = 5: 7156f26ab299 merge-ort: miscellaneous touch-ups
--
gitgitgadget
