This patch series performs a decently-sized refactoring of the revision-walk machinery. Well, "refactoring" is probably the wrong word, as I don't actually remove the old code. Instead, when we see certain options in the 'rev_info' struct, we redirect the commit-walk logic to a new set of methods that distribute the workload differently. By using generation numbers in the commit-graph, we can significantly improve 'git log --graph' commands (and the underlying 'git rev-list --topo-order'). On the Linux repository, I got the following performance results when comparing to the previous version with or without a commit-graph: Test: git rev-list --topo-order -100 HEAD HEAD~1, no commit-graph: 6.80 s HEAD~1, w/ commit-graph: 0.77 s HEAD, w/ commit-graph: 0.02 s Test: git rev-list --topo-order -100 HEAD -- tools HEAD~1, no commit-graph: 9.63 s HEAD~1, w/ commit-graph: 6.06 s HEAD, w/ commit-graph: 0.06 s If you want to read this series but are unfamiliar with the commit-graph and generation numbers, then I recommend reading Documentation/technical/commit-graph.txt or a blob post [1] I wrote on the subject. In particular, the three-part walk described in "revision.c: refactor basic topo-order logic" is present (but underexplained) as an animated PNG [2]. Since revision.c is an incredibly important (and old) portion of the codebase -- and because there are so many orthogonal options in 'struct rev_info' -- I consider this submission to be "RFC quality". That is, I am not confident that I am not missing anything, or that my solution is the best it can be. I did merge this branch with ds/commit-graph-with-grafts and the "DO-NOT-MERGE: write and read commit-graph always" commit that computes a commit-graph with every 'git commit' command. The test suite passed with that change, available on GitHub [3]. To ensure that I cover at least the case I think are interesting, I added tests to t6600-test-reach.sh to verify the walks report the correct results for the three cases there (no commit-graph, full commit-graph, and a partial commit-graph so the walk starts at GENERATION_NUMBER_INFINITY). One notable case that is not included in this series is the case of a history comparison such as 'git rev-list --topo-order A..B'. The existing code in limit_list() has ways to cut the walk short when all pending commits are UNINTERESTING. Since this code depends on commit_list instead of the prio_queue we are using here, I chose to leave it untouched for now. We can revisit it in a separate series later. Since handle_commit() turns on revs->limited when a commit is UNINTERESTING, we do not hit the new code in this case. Removing this 'revs->limited = 1;' line yields correct results, but the performance is worse. This series was based on ds/reachable, but is now based on 'master' to not conflict with 182070 "commit: use timestamp_t for author_date_slab". There is a small conflict with md/filter-trees, because it renamed a flag in revisions.h in the line before I add new flags. Hopefully this conflict is not too difficult to resolve. Changes in V3: I added a new patch that updates the tab-alignment for flags in revision.h before adding new ones (Thanks, Ævar!). Also, I squashed the recommended changes to run_three_modes and test_three_modes from Szeder and Junio. Thanks! Changes in V4: I'm sending a V4 to respond to the feedback so far. Still looking forward to more on the really big commit! * Removed the whitespace changes to the flags in revision.c that caused merge pain. * The prio-queue peek function is now covered by tests when in "stack" mode. * The "add_parents_to_list()" function is now renamed to "process_parents()" * Added a new commit that expands test coverage with alternate orders and file history (use GIT_TEST_COMMIT_GRAPH to have t6012-rev-list-simplify.sh cover the new logic). These tests found a problem with author dates (I forgot to record them during the explore walk). * Commit message edits. Thanks, -Stolee [1] https://blogs.msdn.microsoft.com/devops/2018/07/09/supercharging-the-git-commit-graph-iii-generations/ Supercharging the Git Commit Graph III: Generations and Graph Algorithms [2] https://msdnshared.blob.core.windows.net/media/2018/06/commit-graph-topo-order-b-a.png Animation showing three-part walk [3] https://github.com/derrickstolee/git/tree/topo-order/testA branch containing this series along with commits to compute commit-graph in entire test suite. Cc: avarab@gmail.comCc: szeder.dev@xxxxxxxxx Derrick Stolee (7): prio-queue: add 'peek' operation test-reach: add run_three_modes method test-reach: add rev-list tests revision.c: begin refactoring --topo-order logic commit/revisions: bookkeeping before refactoring revision.c: generation-based topo-order algorithm t6012: make rev-list tests more interesting commit.c | 11 +- commit.h | 8 ++ object.h | 4 +- prio-queue.c | 9 ++ prio-queue.h | 6 + revision.c | 245 +++++++++++++++++++++++++++++++++-- revision.h | 6 + t/helper/test-prio-queue.c | 26 ++-- t/t0009-prio-queue.sh | 14 ++ t/t6012-rev-list-simplify.sh | 45 +++++-- t/t6600-test-reach.sh | 96 +++++++++++++- 11 files changed, 430 insertions(+), 40 deletions(-) base-commit: 2d3b1c576c85b7f5db1f418907af00ab88e0c303 Published-As: https://github.com/gitgitgadget/git/releases/tags/pr-25%2Fderrickstolee%2Ftopo-order%2Fprogress-v4 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-25/derrickstolee/topo-order/progress-v4 Pull-Request: https://github.com/gitgitgadget/git/pull/25 Range-diff vs v3: 1: cc1ec4c270 ! 1: 2358cfd5ed prio-queue: add 'peek' operation @@ -8,7 +8,9 @@ add it as prio_queue_peek(). Add a reference-level comparison in t/helper/test-prio-queue.c - so this method is exercised by t0009-prio-queue.sh. + so this method is exercised by t0009-prio-queue.sh. Further, add + a test that checks the behavior when the compare function is NULL + (i.e. the queue becomes a stack). Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx> @@ -56,6 +58,11 @@ - if (!strcmp(*argv, "get")) - show(prio_queue_get(&pq)); - else if (!strcmp(*argv, "dump")) { +- int *v; +- while ((v = prio_queue_get(&pq))) +- show(v); +- } +- else { + if (!strcmp(*argv, "get")) { + void *peek = prio_queue_peek(&pq); + void *get = prio_queue_get(&pq); @@ -63,6 +70,40 @@ + BUG("peek and get results do not match"); + show(get); + } else if (!strcmp(*argv, "dump")) { - int *v; - while ((v = prio_queue_get(&pq))) - show(v); ++ void *peek; ++ void *get; ++ while ((peek = prio_queue_peek(&pq))) { ++ get = prio_queue_get(&pq); ++ if (peek != get) ++ BUG("peek and get results do not match"); ++ show(get); ++ } ++ } else if (!strcmp(*argv, "stack")) { ++ pq.compare = NULL; ++ } else { + int *v = malloc(sizeof(*v)); + *v = atoi(*argv); + prio_queue_put(&pq, v); + +diff --git a/t/t0009-prio-queue.sh b/t/t0009-prio-queue.sh +--- a/t/t0009-prio-queue.sh ++++ b/t/t0009-prio-queue.sh +@@ + test_cmp expect actual + ' + ++cat >expect <<'EOF' ++3 ++2 ++6 ++4 ++5 ++1 ++8 ++EOF ++test_expect_success 'stack order' ' ++ test-tool prio-queue stack 8 1 5 4 6 2 3 dump >actual && ++ test_cmp expect actual ++' ++ + test_done 2: b2a1ade148 = 2: 3a4b68e479 test-reach: add run_three_modes method 3: b0ceb96076 = 3: 12a3f6d367 test-reach: add rev-list tests 4: fd1a0ab7cd = 4: cd9eef9688 revision.c: begin refactoring --topo-order logic 5: e86f304082 ! 5: f3e291665d commit/revisions: bookkeeping before refactoring @@ -16,7 +16,11 @@ around the UNINTERESTING flag and other special cases depending on the struct rev_info. Allow this method to ignore a NULL 'list' parameter, as we will not be populating the list for our walk. + Also rename the method to the slightly more generic name + process_parents() to make clear that this method does more than + add to a list (and no list is required anymore). + Helped-by: Jeff King <peff@xxxxxxxx> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx> diff --git a/commit.c b/commit.c @@ -28,7 +32,8 @@ -/* record author-date for each commit object */ -define_commit_slab(author_date_slab, timestamp_t); -- ++implement_shared_commit_slab(author_date_slab, timestamp_t); + -static void record_author_date(struct author_date_slab *author_date, - struct commit *commit) +void record_author_date(struct author_date_slab *author_date, @@ -64,7 +69,7 @@ extern int check_commit_signature(const struct commit *commit, struct signature_check *sigc); +/* record author-date for each commit object */ -+define_commit_slab(author_date_slab, timestamp_t); ++define_shared_commit_slab(author_date_slab, timestamp_t); + +void record_author_date(struct author_date_slab *author_date, + struct commit *commit); @@ -77,6 +82,17 @@ diff --git a/revision.c b/revision.c --- a/revision.c +++ b/revision.c +@@ + *cache = new_entry; + } + +-static int add_parents_to_list(struct rev_info *revs, struct commit *commit, +- struct commit_list **list, struct commit_list **cache_ptr) ++static int process_parents(struct rev_info *revs, struct commit *commit, ++ struct commit_list **list, struct commit_list **cache_ptr) + { + struct commit_list *parent = commit->parents; + unsigned left_flag; @@ if (p->object.flags & SEEN) continue; @@ -97,3 +113,39 @@ } if (revs->first_parent_only) break; +@@ + + if (revs->max_age != -1 && (commit->date < revs->max_age)) + obj->flags |= UNINTERESTING; +- if (add_parents_to_list(revs, commit, &list, NULL) < 0) ++ if (process_parents(revs, commit, &list, NULL) < 0) + return -1; + if (obj->flags & UNINTERESTING) { + mark_parents_uninteresting(commit); +@@ + + static void expand_topo_walk(struct rev_info *revs, struct commit *commit) + { +- if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0) { ++ if (process_parents(revs, commit, &revs->commits, NULL) < 0) { + if (!revs->ignore_missing_links) + die("Failed to traverse parents of commit %s", + oid_to_hex(&commit->object.oid)); +@@ + for (;;) { + struct commit *p = *pp; + if (!revs->limited) +- if (add_parents_to_list(revs, p, &revs->commits, &cache) < 0) ++ if (process_parents(revs, p, &revs->commits, &cache) < 0) + return rewrite_one_error; + if (p->object.flags & UNINTERESTING) + return rewrite_one_ok; +@@ + try_to_simplify_commit(revs, commit); + else if (revs->topo_walk_info) + expand_topo_walk(revs, commit); +- else if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0) { ++ else if (process_parents(revs, commit, &revs->commits, NULL) < 0) { + if (!revs->ignore_missing_links) + die("Failed to traverse parents of commit %s", + oid_to_hex(&commit->object.oid)); 6: fa6d5ef152 < -: ---------- revision.h: add whitespace in flag definitions 7: 020b2f50c5 ! 6: aa0bb2221d revision.c: refactor basic topo-order logic @@ -1,6 +1,15 @@ Author: Derrick Stolee <dstolee@xxxxxxxxxxxxx> - revision.c: refactor basic topo-order logic + revision.c: generation-based topo-order algorithm + + The current --topo-order algorithm requires walking all + reachable commits up front, topo-sorting them, all before + outputting the first value. This patch introduces a new + algorithm which uses stored generation numbers to + incrementally walk in topo-order, outputting commits as + we go. This can dramatically reduce the computation time + to write a fixed number of commits, such as when limiting + with "-n <N>" or filling the first page of a pager. When running a command like 'git rev-list --topo-order HEAD', Git performed the following steps: @@ -139,11 +148,12 @@ frequently, including by merge commits. A less-frequently-changed path (such as 'README') has similar end-to-end time since we need to walk the same number of commits (before determining we do not - have 100 hits). However, get get the benefit that the output is + have 100 hits). However, get the benefit that the output is presented to the user as it is discovered, much the same as a normal 'git log' command (no '--topo-order'). This is an improved user experience, even if the command has the same runtime. + Helped-by: Jeff King <peff@xxxxxxxx> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx> diff --git a/object.h b/object.h @@ -216,10 +226,13 @@ + if (parse_commit_gently(c, 1) < 0) + return; + ++ if (revs->sort_order == REV_SORT_BY_AUTHOR_DATE) ++ record_author_date(&info->author_date, c); ++ + if (revs->max_age != -1 && (c->date < revs->max_age)) + c->object.flags |= UNINTERESTING; + -+ if (add_parents_to_list(revs, c, NULL, NULL) < 0) ++ if (process_parents(revs, c, NULL, NULL) < 0) + return; + + if (c->object.flags & UNINTERESTING) @@ -366,10 +379,10 @@ static void expand_topo_walk(struct rev_info *revs, struct commit *commit) { -- if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0) { +- if (process_parents(revs, commit, &revs->commits, NULL) < 0) { + struct commit_list *p; + struct topo_walk_info *info = revs->topo_walk_info; -+ if (add_parents_to_list(revs, commit, NULL, NULL) < 0) { ++ if (process_parents(revs, commit, NULL, NULL) < 0) { if (!revs->ignore_missing_links) die("Failed to traverse parents of commit %s", - oid_to_hex(&commit->object.oid)); @@ -404,9 +417,9 @@ --- a/revision.h +++ b/revision.h @@ - #define USER_GIVEN (1u<<25) /* given directly by the user */ - #define TRACK_LINEAR (1u<<26) - #define ALL_REV_FLAGS (((1u<<11)-1) | USER_GIVEN | TRACK_LINEAR) + #define USER_GIVEN (1u<<25) /* given directly by the user */ + #define TRACK_LINEAR (1u<<26) + #define ALL_REV_FLAGS (((1u<<11)-1) | USER_GIVEN | TRACK_LINEAR) +#define TOPO_WALK_EXPLORED (1u<<27) +#define TOPO_WALK_INDEGREE (1u<<28) -: ---------- > 7: a21febe112 t6012: make rev-list tests more interesting -- gitgitgadget
