From patchwork Thu Nov 1 13:46:22 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Derrick Stolee X-Patchwork-Id: 10663983 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E9D7B13B5 for ; Thu, 1 Nov 2018 13:46:38 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id DEB522BBC3 for ; Thu, 1 Nov 2018 13:46:38 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id D29012BC7B; Thu, 1 Nov 2018 13:46:38 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.0 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CBAD62BBC3 for ; Thu, 1 Nov 2018 13:46:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728733AbeKAWti (ORCPT ); Thu, 1 Nov 2018 18:49:38 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:36066 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728520AbeKAWth (ORCPT ); Thu, 1 Nov 2018 18:49:37 -0400 Received: by mail-qk1-f194.google.com with SMTP id o125so9008623qkf.3 for ; Thu, 01 Nov 2018 06:46:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=O2sygxFRdpNLh2nFaKhC0enBudJmWRhoL/D7OHWBiQE=; b=RDMmnwCayyL9Cijt34LYP4ualXiSjypFegb687fs5nmOGm7MwAW7NKjasyFTmyAEKY O9dOKAn38Y5KSKgkKluTXJrq94hrrEBqSt8p9bsW4RpJiziX2CQiaWr9Gg5SHyzzW6t9 SFLKNaMW06nrpsj5cd0NTVNiPe/ZjSVz7VvH5JAvs8aF5XF9eaKXi0hYN7fKXbTph4ma oTcGlgBy3Ot+kHn/Nm8QOe7t4uYcepyCIeg7i1gW6R22SceqLNGPOQJsCJHVizwtK8pG 9LCUgkfc7PEVG2z8uxKYd9uj98ugoXEfH4PP58RBWm9hlvM7y4jsZPHyEtJGCLDAhQ23 kbow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=O2sygxFRdpNLh2nFaKhC0enBudJmWRhoL/D7OHWBiQE=; b=LKxhu2fq7fM+3R2XQrRISNZs1W8uCV3XNs6/xWK612zBdzjLQHvUiXhMdLZ0bSDnfM WJ7M3UgVDRbD5GglFxYqA3pZGjqDHZbnj1RnyphgFHBuhXw/oIVpdzQnwcS9jZ4+UAdj uZLWMg6U8juvZeO+/jd/B1smzg/AOycg2EKfG+snFTLJ6zwa3pvhGL7WRbC644aWhTe5 OXHj6KrDurCWgoX5HbiWbeK2GA+gHsbS6UfZ2GFE/1cB77WMLP59lfaX1ZG8M6RoF3QZ 8UuPrQrnvXcQywgrSFt2n+1AwzCtQ8Wbnvz40hiFscq/Fi6Zh40DORA/WoSqASrgSRf2 7FlQ== X-Gm-Message-State: AGRZ1gJ2iEWyS4/br0D9qosY2KqNug6OurAUrbb4zMOxLVeV3kWacr9e XS92+wFZI3bY8+XW9APROuWQC/Rq X-Google-Smtp-Source: AJdET5cSDbZ3kVzw2sLgvCyNg21QcS/dH/GX4qQvYklDilbEOV66c5GaLf3Ex/xJ9bgQYsPblCrBqw== X-Received: by 2002:ae9:e414:: with SMTP id q20mr6433425qkc.205.1541079993377; Thu, 01 Nov 2018 06:46:33 -0700 (PDT) Received: from stolee-linux.mshome.net ([167.220.148.125]) by smtp.gmail.com with ESMTPSA id f75sm7347357qkf.96.2018.11.01.06.46.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 01 Nov 2018 06:46:32 -0700 (PDT) From: Derrick Stolee X-Google-Original-From: Derrick Stolee To: git@vger.kernel.org Cc: gitster@pobox.com, avarab@gmail.com, szeder.dev@gmail.com, peff@peff.net, jnareb@gmail.com, Derrick Stolee Subject: [PATCH v5 6/7] revision.c: generation-based topo-order algorithm Date: Thu, 1 Nov 2018 13:46:22 +0000 Message-Id: <20181101134623.84055-7-dstolee@microsoft.com> X-Mailer: git-send-email 2.19.1.542.gc4df23f792 In-Reply-To: <20181101134623.84055-1-dstolee@microsoft.com> References: <20181101134623.84055-1-dstolee@microsoft.com> MIME-Version: 1.0 Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 " or filling the first page of a pager. When running a command like 'git rev-list --topo-order HEAD', Git performed the following steps: 1. Run limit_list(), which parses all reachable commits, adds them to a linked list, and distributes UNINTERESTING flags. If all unprocessed commits are UNINTERESTING, then it may terminate without walking all reachable commits. This does not occur if we do not specify UNINTERESTING commits. 2. Run sort_in_topological_order(), which is an implementation of Kahn's algorithm. It first iterates through the entire set of important commits and computes the in-degree of each (plus one, as we use 'zero' as a special value here). Then, we walk the commits in priority order, adding them to the priority queue if and only if their in-degree is one. As we remove commits from this priority queue, we decrement the in-degree of their parents. 3. While we are peeling commits for output, get_revision_1() uses pop_commit on the full list of commits computed by sort_in_topological_order(). In the new algorithm, these three steps correspond to three different commit walks. We run these walks simultaneously, and advance each only as far as necessary to satisfy the requirements of the 'higher order' walk. We know when we can pause each walk by using generation numbers from the commit- graph feature. Recall that the generation number of a commit satisfies: * If the commit has at least one parent, then the generation number is one more than the maximum generation number among its parents. * If the commit has no parent, then the generation number is one. There are two special generation numbers: * GENERATION_NUMBER_INFINITY: this value is 0xffffffff and indicates that the commit is not stored in the commit-graph and the generation number was not previously calculated. * GENERATION_NUMBER_ZERO: this value (0) is a special indicator to say that the commit-graph was generated by a version of Git that does not compute generation numbers (such as v2.18.0). Since we use generation_numbers_enabled() before using the new algorithm, we do not need to worry about GENERATION_NUMBER_ZERO. However, the existence of GENERATION_NUMBER_INFINITY implies the following weaker statement than the usual we expect from generation numbers: If A and B are commits with generation numbers gen(A) and gen(B) and gen(A) < gen(B), then A cannot reach B. Thus, we will walk in each of our stages until the "maximum unexpanded generation number" is strictly lower than the generation number of a commit we are about to use. The walks are as follows: 1. EXPLORE: using the explore_queue priority queue (ordered by maximizing the generation number), parse each reachable commit until all commits in the queue have generation number strictly lower than needed. During this walk, update the UNINTERESTING flags as necessary. 2. INDEGREE: using the indegree_queue priority queue (ordered by maximizing the generation number), add one to the in- degree of each parent for each commit that is walked. Since we walk in order of decreasing generation number, we know that discovering an in-degree value of 0 means the value for that commit was not initialized, so should be initialized to two. (Recall that in-degree value "1" is what we use to say a commit is ready for output.) As we iterate the parents of a commit during this walk, ensure the EXPLORE walk has walked beyond their generation numbers. 3. TOPO: using the topo_queue priority queue (ordered based on the sort_order given, which could be commit-date, author- date, or typical topo-order which treats the queue as a LIFO stack), remove a commit from the queue and decrement the in-degree of each parent. If a parent has an in-degree of one, then we add it to the topo_queue. Before we decrement the in-degree, however, ensure the INDEGREE walk has walked beyond that generation number. The implementations of these walks are in the following methods: * explore_walk_step and explore_to_depth * indegree_walk_step and compute_indegrees_to_depth * next_topo_commit and expand_topo_walk These methods have some patterns that may seem strange at first, but they are probably carry-overs from their equivalents in limit_list and sort_in_topological_order. One thing that is missing from this implementation is a proper way to stop walking when the entire queue is UNINTERESTING, so this implementation is not enabled by comparisions, such as in 'git rev-list --topo-order A..B'. This can be updated in the future. In my local testing, I used the following Git commands on the Linux repository in three modes: HEAD~1 with no commit-graph, HEAD~1 with a commit-graph, and HEAD with a commit-graph. This allows comparing the benefits we get from parsing commits from the commit-graph and then again the benefits we get by restricting the set of commits we walk. 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 This speedup is due to a few things. First, the new generation- number-enabled algorithm walks commits on order of the number of results output (subject to some branching structure expectations). Since we limit to 100 results, we are running a query similar to filling a single page of results. Second, when specifying a path, we must parse the root tree object for each commit we walk. The previous benefits from the commit-graph are entirely from reading the commit-graph instead of parsing commits. Since we need to parse trees for the same number of commits as before, we slow down significantly from the non-path-based query. For the test above, I specifically selected a path that is changed 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 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 Signed-off-by: Derrick Stolee --- object.h | 4 +- revision.c | 195 +++++++++++++++++++++++++++++++++++++++++++++++++++-- revision.h | 2 + 3 files changed, 194 insertions(+), 7 deletions(-) diff --git a/object.h b/object.h index 0feb90ae61..796792cb32 100644 --- a/object.h +++ b/object.h @@ -59,7 +59,7 @@ struct object_array { /* * object flag allocation: - * revision.h: 0---------10 2526 + * revision.h: 0---------10 25----28 * fetch-pack.c: 01 * negotiator/default.c: 2--5 * walker.c: 0-2 @@ -78,7 +78,7 @@ struct object_array { * builtin/show-branch.c: 0-------------------------------------------26 * builtin/unpack-objects.c: 2021 */ -#define FLAG_BITS 27 +#define FLAG_BITS 29 /* * The object type is stored in 3 bits. diff --git a/revision.c b/revision.c index 36458265a0..4ef47d2fb4 100644 --- a/revision.c +++ b/revision.c @@ -26,6 +26,7 @@ #include "argv-array.h" #include "commit-reach.h" #include "commit-graph.h" +#include "prio-queue.h" volatile show_early_output_fn_t show_early_output; @@ -2895,31 +2896,215 @@ static int mark_uninteresting(const struct object_id *oid, return 0; } -struct topo_walk_info {}; +define_commit_slab(indegree_slab, int); +define_commit_slab(author_date_slab, timestamp_t); + +struct topo_walk_info { + uint32_t min_generation; + struct prio_queue explore_queue; + struct prio_queue indegree_queue; + struct prio_queue topo_queue; + struct indegree_slab indegree; + struct author_date_slab author_date; +}; + +static inline void test_flag_and_insert(struct prio_queue *q, struct commit *c, int flag) +{ + if (c->object.flags & flag) + return; + + c->object.flags |= flag; + prio_queue_put(q, c); +} + +static void explore_walk_step(struct rev_info *revs) +{ + struct topo_walk_info *info = revs->topo_walk_info; + struct commit_list *p; + struct commit *c = prio_queue_get(&info->explore_queue); + + if (!c) + return; + + 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 (process_parents(revs, c, NULL, NULL) < 0) + return; + + if (c->object.flags & UNINTERESTING) + mark_parents_uninteresting(c); + + for (p = c->parents; p; p = p->next) + test_flag_and_insert(&info->explore_queue, p->item, TOPO_WALK_EXPLORED); +} + +static void explore_to_depth(struct rev_info *revs, + uint32_t gen_cutoff) +{ + struct topo_walk_info *info = revs->topo_walk_info; + struct commit *c; + while ((c = prio_queue_peek(&info->explore_queue)) && + c->generation >= gen_cutoff) + explore_walk_step(revs); +} + +static void indegree_walk_step(struct rev_info *revs) +{ + struct commit_list *p; + struct topo_walk_info *info = revs->topo_walk_info; + struct commit *c = prio_queue_get(&info->indegree_queue); + + if (!c) + return; + + if (parse_commit_gently(c, 1) < 0) + return; + + explore_to_depth(revs, c->generation); + + for (p = c->parents; p; p = p->next) { + struct commit *parent = p->item; + int *pi = indegree_slab_at(&info->indegree, parent); + + if (*pi) + (*pi)++; + else + *pi = 2; + + test_flag_and_insert(&info->indegree_queue, parent, TOPO_WALK_INDEGREE); + + if (revs->first_parent_only) + return; + } +} + +static void compute_indegrees_to_depth(struct rev_info *revs, + uint32_t gen_cutoff) +{ + struct topo_walk_info *info = revs->topo_walk_info; + struct commit *c; + while ((c = prio_queue_peek(&info->indegree_queue)) && + c->generation >= gen_cutoff) + indegree_walk_step(revs); +} static void init_topo_walk(struct rev_info *revs) { struct topo_walk_info *info; + struct commit_list *list; revs->topo_walk_info = xmalloc(sizeof(struct topo_walk_info)); info = revs->topo_walk_info; memset(info, 0, sizeof(struct topo_walk_info)); - limit_list(revs); - sort_in_topological_order(&revs->commits, revs->sort_order); + init_indegree_slab(&info->indegree); + memset(&info->explore_queue, 0, sizeof(info->explore_queue)); + memset(&info->indegree_queue, 0, sizeof(info->indegree_queue)); + memset(&info->topo_queue, 0, sizeof(info->topo_queue)); + + switch (revs->sort_order) { + default: /* REV_SORT_IN_GRAPH_ORDER */ + info->topo_queue.compare = NULL; + break; + case REV_SORT_BY_COMMIT_DATE: + info->topo_queue.compare = compare_commits_by_commit_date; + break; + case REV_SORT_BY_AUTHOR_DATE: + init_author_date_slab(&info->author_date); + info->topo_queue.compare = compare_commits_by_author_date; + info->topo_queue.cb_data = &info->author_date; + break; + } + + info->explore_queue.compare = compare_commits_by_gen_then_commit_date; + info->indegree_queue.compare = compare_commits_by_gen_then_commit_date; + + info->min_generation = GENERATION_NUMBER_INFINITY; + for (list = revs->commits; list; list = list->next) { + struct commit *c = list->item; + + if (parse_commit_gently(c, 1)) + continue; + + test_flag_and_insert(&info->explore_queue, c, TOPO_WALK_EXPLORED); + test_flag_and_insert(&info->indegree_queue, c, TOPO_WALK_INDEGREE); + + if (c->generation < info->min_generation) + info->min_generation = c->generation; + + *(indegree_slab_at(&info->indegree, c)) = 1; + + if (revs->sort_order == REV_SORT_BY_AUTHOR_DATE) + record_author_date(&info->author_date, c); + } + compute_indegrees_to_depth(revs, info->min_generation); + + for (list = revs->commits; list; list = list->next) { + struct commit *c = list->item; + + if (*(indegree_slab_at(&info->indegree, c)) == 1) + prio_queue_put(&info->topo_queue, c); + } + + /* + * This is unfortunate; the initial tips need to be shown + * in the order given from the revision traversal machinery. + */ + if (revs->sort_order == REV_SORT_IN_GRAPH_ORDER) + prio_queue_reverse(&info->topo_queue); } static struct commit *next_topo_commit(struct rev_info *revs) { - return pop_commit(&revs->commits); + struct commit *c; + struct topo_walk_info *info = revs->topo_walk_info; + + /* pop next off of topo_queue */ + c = prio_queue_get(&info->topo_queue); + + if (c) + *(indegree_slab_at(&info->indegree, c)) = 0; + + return c; } static void expand_topo_walk(struct rev_info *revs, struct commit *commit) { - if (process_parents(revs, commit, &revs->commits, NULL) < 0) { + struct commit_list *p; + struct topo_walk_info *info = revs->topo_walk_info; + 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)); } + + for (p = commit->parents; p; p = p->next) { + struct commit *parent = p->item; + int *pi; + + if (parse_commit_gently(parent, 1) < 0) + continue; + + if (parent->generation < info->min_generation) { + info->min_generation = parent->generation; + compute_indegrees_to_depth(revs, info->min_generation); + } + + pi = indegree_slab_at(&info->indegree, parent); + + (*pi)--; + if (*pi == 1) + prio_queue_put(&info->topo_queue, parent); + + if (revs->first_parent_only) + return; + } } int prepare_revision_walk(struct rev_info *revs) diff --git a/revision.h b/revision.h index fd4154ff75..b0b3bb8025 100644 --- a/revision.h +++ b/revision.h @@ -24,6 +24,8 @@ #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) #define DECORATE_SHORT_REFS 1 #define DECORATE_FULL_REFS 2