From 671c9b7e315db89081cc69f83a8f405e4aca37bc Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Thu, 13 Nov 2008 16:36:30 -0800 Subject: [PATCH 1/2] Add cache preload facility This can do the lstat() storm in parallel, giving potentially much improved performance for cold-cache cases or things like NFS that have weak metadata caching. Just use "read_cache_preload()" instead of "read_cache()" to force an optimistic preload of the index stat data. The function takes a pathspec as its argument, allowing us to preload only the relevant portion of the index. Signed-off-by: Linus Torvalds Signed-off-by: Junio C Hamano --- Documentation/config.txt | 9 ++++ Makefile | 1 + builtin-commit.c | 8 ++-- builtin-diff-files.c | 4 +- builtin-diff.c | 8 ++-- cache.h | 3 ++ config.c | 5 +++ environment.c | 3 ++ preload-index.c | 91 ++++++++++++++++++++++++++++++++++++++++ 9 files changed, 122 insertions(+), 10 deletions(-) create mode 100644 preload-index.c diff --git a/Documentation/config.txt b/Documentation/config.txt index 32dcd643d2..0d96e763ac 100644 --- a/Documentation/config.txt +++ b/Documentation/config.txt @@ -413,6 +413,15 @@ data writes properly, but can be useful for filesystems that do not use journalling (traditional UNIX filesystems) or that only journal metadata and not file contents (OS X's HFS+, or Linux ext3 with "data=writeback"). +core.preloadindex:: + Enable parallel index preload for operations like 'git diff' ++ +This can speed up operations like 'git diff' and 'git status' especially +on filesystems like NFS that have weak caching semantics and thus +relatively high IO latencies. With this set to 'true', git will do the +index comparison to the filesystem data in parallel, allowing +overlapping IO's. + alias.*:: Command aliases for the linkgit:git[1] command wrapper - e.g. after defining "alias.last = cat-file commit HEAD", the invocation diff --git a/Makefile b/Makefile index 35adafa011..acac0ae5d9 100644 --- a/Makefile +++ b/Makefile @@ -496,6 +496,7 @@ LIB_OBJS += write_or_die.o LIB_OBJS += ws.o LIB_OBJS += wt-status.o LIB_OBJS += xdiff-interface.o +LIB_OBJS += preload-index.o BUILTIN_OBJS += builtin-add.o BUILTIN_OBJS += builtin-annotate.o diff --git a/builtin-commit.c b/builtin-commit.c index 591d16b91e..1677e6b45f 100644 --- a/builtin-commit.c +++ b/builtin-commit.c @@ -225,18 +225,18 @@ static char *prepare_index(int argc, const char **argv, const char *prefix) if (interactive) { interactive_add(argc, argv, prefix); - if (read_cache() < 0) + if (read_cache_preload(NULL) < 0) die("index file corrupt"); commit_style = COMMIT_AS_IS; return get_index_file(); } - if (read_cache() < 0) - die("index file corrupt"); - if (*argv) pathspec = get_pathspec(prefix, argv); + if (read_cache_preload(pathspec) < 0) + die("index file corrupt"); + /* * Non partial, non as-is commit. * diff --git a/builtin-diff-files.c b/builtin-diff-files.c index 2b578c714d..5b64011de8 100644 --- a/builtin-diff-files.c +++ b/builtin-diff-files.c @@ -59,8 +59,8 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix) (rev.diffopt.output_format & DIFF_FORMAT_PATCH)) rev.combine_merges = rev.dense_combined_merges = 1; - if (read_cache() < 0) { - perror("read_cache"); + if (read_cache_preload(rev.diffopt.paths) < 0) { + perror("read_cache_preload"); return -1; } result = run_diff_files(&rev, options); diff --git a/builtin-diff.c b/builtin-diff.c index 7ceceeb6ff..1447c1d6ba 100644 --- a/builtin-diff.c +++ b/builtin-diff.c @@ -134,8 +134,8 @@ static int builtin_diff_index(struct rev_info *revs, revs->max_count != -1 || revs->min_age != -1 || revs->max_age != -1) usage(builtin_diff_usage); - if (read_cache() < 0) { - perror("read_cache"); + if (read_cache_preload(revs->diffopt.paths) < 0) { + perror("read_cache_preload"); return -1; } return run_diff_index(revs, cached); @@ -234,8 +234,8 @@ static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv revs->combine_merges = revs->dense_combined_merges = 1; setup_work_tree(); - if (read_cache() < 0) { - perror("read_cache"); + if (read_cache_preload(revs->diffopt.paths) < 0) { + perror("read_cache_preload"); return -1; } result = run_diff_files(revs, options); diff --git a/cache.h b/cache.h index 3b5f0c4c00..685a8666b6 100644 --- a/cache.h +++ b/cache.h @@ -262,6 +262,7 @@ static inline void remove_name_hash(struct cache_entry *ce) #define read_cache() read_index(&the_index) #define read_cache_from(path) read_index_from(&the_index, (path)) +#define read_cache_preload(pathspec) read_index_preload(&the_index, (pathspec)) #define is_cache_unborn() is_index_unborn(&the_index) #define read_cache_unmerged() read_index_unmerged(&the_index) #define write_cache(newfd, cache, entries) write_index(&the_index, (newfd)) @@ -368,6 +369,7 @@ extern int init_db(const char *template_dir, unsigned int flags); /* Initialize and use the cache information */ extern int read_index(struct index_state *); +extern int read_index_preload(struct index_state *, const char **pathspec); extern int read_index_from(struct index_state *, const char *path); extern int is_index_unborn(struct index_state *); extern int read_index_unmerged(struct index_state *); @@ -458,6 +460,7 @@ extern size_t packed_git_limit; extern size_t delta_base_cache_limit; extern int auto_crlf; extern int fsync_object_files; +extern int core_preload_index; enum safe_crlf { SAFE_CRLF_FALSE = 0, diff --git a/config.c b/config.c index 67cc1dcad0..d2fc8f5f22 100644 --- a/config.c +++ b/config.c @@ -490,6 +490,11 @@ static int git_default_core_config(const char *var, const char *value) return 0; } + if (!strcmp(var, "core.preloadindex")) { + core_preload_index = git_config_bool(var, value); + return 0; + } + /* Add other config variables here and to Documentation/config.txt. */ return 0; } diff --git a/environment.c b/environment.c index bb96ac0a71..e278bce0ea 100644 --- a/environment.c +++ b/environment.c @@ -43,6 +43,9 @@ unsigned whitespace_rule_cfg = WS_DEFAULT_RULE; enum branch_track git_branch_track = BRANCH_TRACK_REMOTE; enum rebase_setup_type autorebase = AUTOREBASE_NEVER; +/* Parallel index stat data preload? */ +int core_preload_index = 0; + /* This is set by setup_git_dir_gently() and/or git_default_config() */ char *git_work_tree_cfg; static char *work_tree; diff --git a/preload-index.c b/preload-index.c new file mode 100644 index 0000000000..6253578c96 --- /dev/null +++ b/preload-index.c @@ -0,0 +1,91 @@ +/* + * Copyright (C) 2008 Linus Torvalds + */ +#include "cache.h" +#include + +/* + * Mostly randomly chosen maximum thread counts: we + * cap the parallelism to 20 threads, and we want + * to have at least 500 lstat's per thread for it to + * be worth starting a thread. + */ +#define MAX_PARALLEL (20) +#define THREAD_COST (500) + +struct thread_data { + pthread_t pthread; + struct index_state *index; + const char **pathspec; + int offset, nr; +}; + +static void *preload_thread(void *_data) +{ + int nr; + struct thread_data *p = _data; + struct index_state *index = p->index; + struct cache_entry **cep = index->cache + p->offset; + + nr = p->nr; + if (nr + p->offset > index->cache_nr) + nr = index->cache_nr - p->offset; + + do { + struct cache_entry *ce = *cep++; + struct stat st; + + if (ce_stage(ce)) + continue; + if (ce_uptodate(ce)) + continue; + if (!ce_path_match(ce, p->pathspec)) + continue; + if (lstat(ce->name, &st)) + continue; + if (ie_match_stat(index, ce, &st, 0)) + continue; + ce_mark_uptodate(ce); + } while (--nr > 0); + return NULL; +} + +static void preload_index(struct index_state *index, const char **pathspec) +{ + int threads, i, work, offset; + struct thread_data data[MAX_PARALLEL]; + + if (!core_preload_index) + return; + + threads = index->cache_nr / THREAD_COST; + if (threads < 2) + return; + if (threads > MAX_PARALLEL) + threads = MAX_PARALLEL; + offset = 0; + work = (index->cache_nr + threads - 1) / threads; + for (i = 0; i < threads; i++) { + struct thread_data *p = data+i; + p->index = index; + p->pathspec = pathspec; + p->offset = offset; + p->nr = work; + offset += work; + if (pthread_create(&p->pthread, NULL, preload_thread, p)) + die("unable to create threaded lstat"); + } + for (i = 0; i < threads; i++) { + struct thread_data *p = data+i; + if (pthread_join(p->pthread, NULL)) + die("unable to join threaded lstat"); + } +} + +int read_index_preload(struct index_state *index, const char **pathspec) +{ + int retval = read_index(index); + + preload_index(index, pathspec); + return retval; +} From 7c4ea599b0d44e46c4f96bf955b62d96126b53ff Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 17 Nov 2008 09:01:20 -0800 Subject: [PATCH 2/2] Fix index preloading for racy dirty case In the threaded index preloading case, we must be sure to always use the CE_MATCH_RACY_IS_DIRTY flag when calling ie_match_stat(), in order to make sure that we only ever look at the stat() data, and don't try to do anything fancy. Because most of git internals are not thread-safe, and must not be called in parallel. Otherwise, what happens is that if the timestamps indicate that an entry _might_ be dirty, we might start actually comparing filesystem data with the object database. And we mustn't do that, because that would involve looking up and creating the object structure, and that whole code sequence with read_sha1_file() where we look up and add objects to the hashes is definitely not thread-safe. Nor do we want to add locking, because the whole point of the preload was to be simple and not affect anything else. With CE_MATCH_RACY_IS_DIRTY, we get what we wanted, and we'll just leave the hard cases well alone, to be done later in the much simpler serial case. Signed-off-by: Linus Torvalds Signed-off-by: Junio C Hamano --- preload-index.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/preload-index.c b/preload-index.c index 6253578c96..a6855837a4 100644 --- a/preload-index.c +++ b/preload-index.c @@ -43,7 +43,7 @@ static void *preload_thread(void *_data) continue; if (lstat(ce->name, &st)) continue; - if (ie_match_stat(index, ce, &st, 0)) + if (ie_match_stat(index, ce, &st, CE_MATCH_RACY_IS_DIRTY)) continue; ce_mark_uptodate(ce); } while (--nr > 0);