From dfa8bae5a20ead0737413fec5c7bb754fe538abe Mon Sep 17 00:00:00 2001 From: Phillip Wood Date: Thu, 23 Sep 2021 15:26:20 +0000 Subject: [PATCH 1/2] sequencer.c: factor out a function This code is heavily indented and obscures the high level logic within the loop. Let's move it to its own function before modifying it in the next commit. Note that there is a subtle change in behavior if the todo list cannot be reread. Previously todo_list->current was incremented before returning, now it returns immediately. Signed-off-by: Phillip Wood Signed-off-by: Junio C Hamano --- sequencer.c | 38 ++++++++++++++++++++++++-------------- 1 file changed, 24 insertions(+), 14 deletions(-) diff --git a/sequencer.c b/sequencer.c index 7f07cd00f3..a248c886c2 100644 --- a/sequencer.c +++ b/sequencer.c @@ -4254,6 +4254,27 @@ static int stopped_at_head(struct repository *r) } +static int reread_todo_if_changed(struct repository *r, + struct todo_list *todo_list, + struct replay_opts *opts) +{ + struct stat st; + + if (stat(get_todo_path(opts), &st)) { + return error_errno(_("could not stat '%s'"), + get_todo_path(opts)); + } else if (match_stat_data(&todo_list->stat, &st)) { + /* Reread the todo file if it has changed. */ + todo_list_release(todo_list); + if (read_populate_todo(r, todo_list, opts)) + return -1; /* message was printed */ + /* `current` will be incremented on return */ + todo_list->current = -1; + } + + return 0; +} + static const char rescheduled_advice[] = N_("Could not execute the todo command\n" "\n" @@ -4433,20 +4454,9 @@ static int pick_commits(struct repository *r, item->commit, arg, item->arg_len, opts, res, 0); - } else if (is_rebase_i(opts) && check_todo && !res) { - struct stat st; - - if (stat(get_todo_path(opts), &st)) { - res = error_errno(_("could not stat '%s'"), - get_todo_path(opts)); - } else if (match_stat_data(&todo_list->stat, &st)) { - /* Reread the todo file if it has changed. */ - todo_list_release(todo_list); - if (read_populate_todo(r, todo_list, opts)) - res = -1; /* message was printed */ - /* `current` will be incremented below */ - todo_list->current = -1; - } + } else if (is_rebase_i(opts) && check_todo && !res && + reread_todo_if_changed(r, todo_list, opts)) { + return -1; } todo_list->current++; From 2b88fe0603a93314b96f94b22e197b7b1b838c80 Mon Sep 17 00:00:00 2001 From: Phillip Wood Date: Thu, 23 Sep 2021 15:26:21 +0000 Subject: [PATCH 2/2] rebase: fix todo-list rereading MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 54fd3243da ("rebase -i: reread the todo list if `exec` touched it", 2017-04-26) sought to reread the todo list after running an exec command only if it had been changed. To accomplish this it checks the stat data of the todo list after running an exec command to see if it has changed. Unfortunately there are two problems, firstly the implementation is buggy we actually reread the list after each exec which is quadratic in the number of commit lookups and secondly the design is predicated on using nanosecond time stamps which are not the default. The implementation bug stems from the fact that we write a new todo list to disk before running each command but do not update the stat data to reflect this[1]. The design problem is that it is possible for the user to edit the todo list without changing its size or inode which means we have to rely on the mtime to tell us if it has changed. Unfortunately unless git is built with USE_NSEC it is possible for the original and edited list to share the same mtime. Ideally "git rebase --edit-todo" would set a flag that we would then check in sequencer.c. Unfortunately this is approach will not work as there are scripts in the wild that write to the todo list directly without running "git rebase --edit-todo". Instead of relying on stat data this patch simply reads the possibly edited todo list and compares it to the original with memcmp(). This is much faster than reparsing the todo list each time. This patch reduces the time to run git rebase -r -xtrue v2.32.0~100 v2.32.0 which runs 419 exec commands by 6.6%. For comparison fixing the implementation bug in stat based approach reduces the time by a further 1.4% and is indistinguishable from never rereading the todo list. [1] https://lore.kernel.org/git/20191125131833.GD23183@szeder.dev/ Reported-by: SZEDER Gábor Signed-off-by: Phillip Wood Signed-off-by: Junio C Hamano --- sequencer.c | 19 ++++++++----------- sequencer.h | 1 - 2 files changed, 8 insertions(+), 12 deletions(-) diff --git a/sequencer.c b/sequencer.c index a248c886c2..d51440ddcd 100644 --- a/sequencer.c +++ b/sequencer.c @@ -2671,7 +2671,6 @@ static int read_populate_todo(struct repository *r, struct todo_list *todo_list, struct replay_opts *opts) { - struct stat st; const char *todo_file = get_todo_path(opts); int res; @@ -2679,11 +2678,6 @@ static int read_populate_todo(struct repository *r, if (strbuf_read_file_or_whine(&todo_list->buf, todo_file) < 0) return -1; - res = stat(todo_file, &st); - if (res) - return error(_("could not stat '%s'"), todo_file); - fill_stat_data(&todo_list->stat, &st); - res = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list); if (res) { if (is_rebase_i(opts)) @@ -4258,12 +4252,14 @@ static int reread_todo_if_changed(struct repository *r, struct todo_list *todo_list, struct replay_opts *opts) { - struct stat st; + int offset; + struct strbuf buf = STRBUF_INIT; - if (stat(get_todo_path(opts), &st)) { - return error_errno(_("could not stat '%s'"), - get_todo_path(opts)); - } else if (match_stat_data(&todo_list->stat, &st)) { + if (strbuf_read_file_or_whine(&buf, get_todo_path(opts)) < 0) + return -1; + offset = get_item_line_offset(todo_list, todo_list->current + 1); + if (buf.len != todo_list->buf.len - offset || + memcmp(buf.buf, todo_list->buf.buf + offset, buf.len)) { /* Reread the todo file if it has changed. */ todo_list_release(todo_list); if (read_populate_todo(r, todo_list, opts)) @@ -4271,6 +4267,7 @@ static int reread_todo_if_changed(struct repository *r, /* `current` will be incremented on return */ todo_list->current = -1; } + strbuf_release(&buf); return 0; } diff --git a/sequencer.h b/sequencer.h index d57d8ea23d..cdeb0c6be4 100644 --- a/sequencer.h +++ b/sequencer.h @@ -116,7 +116,6 @@ struct todo_list { struct todo_item *items; int nr, alloc, current; int done_nr, total_nr; - struct stat_data stat; }; #define TODO_LIST_INIT { STRBUF_INIT }