[PATCH 3/4] pack-objects: don't traverse objects unnecessarily
- From
Dan McGee <dpmcgee@gmail.com>
- Date
- Oct 18, 2011, 05:21 UTC
- Message-ID
- <1318915284-6361-3-git-send-email-dpmcgee@gmail.com>
- In-Reply-To
- <1318915284-6361-1-git-send-email-dpmcgee@gmail.com>
This brings back some of the performance lost in optimizing recency order inside pack objects. We were doing extreme amounts of object re-traversal: for the 2.14 million objects in the Linux kernel repository, we were calling add_to_write_order() over 1.03 billion times (a 0.2% hit rate, making 99.8% of of these calls extraneous).
Two optimizations take place here- we can start our objects array iteration from a known point where we left off before we started trying to find our tags, and we don't need to do the deep dives required by add_family_to_write_order() if the object has already been marked as filled.
These two optimizations bring some pretty spectacular results via `perf stat`:
task-clock: 83373 ms --> 43800 ms (50% faster) cycles: 221,633,461,676 --> 116,307,209,986 (47% fewer) instructions: 149,299,179,939 --> 122,998,800,184 (18% fewer)
Signed-off-by: Dan McGee <dpmcgee@gmail.com> --- builtin/pack-objects.c | 18 ++++++++++++------ 1 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c index 0de10d2..d9fb202 100644 --- a/builtin/pack-objects.c +++ b/builtin/pack-objects.c @@ -490,7 +490,7 @@ static void add_family_to_write_order(struct object_entry **wo, static struct object_entry **compute_write_order(void) { - unsigned int i, wo_end; + unsigned int i, wo_end, last_untagged; struct object_entry **wo = xmalloc(nr_objects * sizeof(*wo)); @@ -521,7 +521,7 @@ static struct object_entry **compute_write_order(void) for_each_tag_ref(mark_tagged, NULL); /* - * Give the commits in the original recency order until + * Give the objects in the original recency order until * we see a tagged tip. */ for (i = wo_end = 0; i < nr_objects; i++) { @@ -529,6 +529,7 @@ static struct object_entry **compute_write_order(void) break; add_to_write_order(wo, &wo_end, &objects[i]); } + last_untagged = i; /* * Then fill all the tagged tips. @@ -541,7 +542,7 @@ static struct object_entry **compute_write_order(void) /* * And then all remaining commits and tags. */ - for (i = 0; i < nr_objects; i++) { + for (i = last_untagged; i < nr_objects; i++) { if (objects[i].type != OBJ_COMMIT && objects[i].type != OBJ_TAG) continue; @@ -551,7 +552,7 @@ static struct object_entry **compute_write_order(void) /* * And then all the trees. */ - for (i = 0; i < nr_objects; i++) { + for (i = last_untagged; i < nr_objects; i++) { if (objects[i].type != OBJ_TREE) continue; add_to_write_order(wo, &wo_end, &objects[i]); @@ -560,8 +561,13 @@ static struct object_entry **compute_write_order(void) /* * Finally all the rest in really tight order */ - for (i = 0; i < nr_objects; i++) - add_family_to_write_order(wo, &wo_end, &objects[i]); + for (i = last_untagged; i < nr_objects; i++) { + if (!objects[i].filled) + add_family_to_write_order(wo, &wo_end, &objects[i]); + } + + if(wo_end != nr_objects) + die("ordered %u objects, expected %u", wo_end, nr_objects); return wo; }
-- 1.7.7