From: Taylor Blau <me@ttaylorr.com>
To: Abhradeep Chakraborty via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Kaartic Sivaram <kaartic.sivaraam@gmail.com>,
Derrick Stolee <derrickstolee@github.com>,
Abhradeep Chakraborty <chakrabortyabhradeep79@gmail.com>
Subject: Re: [PATCH v3 4/6] pack-bitmap: prepare to read lookup table extension
Date: Thu, 14 Jul 2022 22:46:38 -0400 [thread overview]
Message-ID: <YtDVDu7VKgAcvRse@nand.local> (raw)
In-Reply-To: <e64362621d235f2c79f52e984de7a2a2794e2842.1656924376.git.gitgitgadget@gmail.com>
On Mon, Jul 04, 2022 at 08:46:14AM +0000, Abhradeep Chakraborty via GitGitGadget wrote:
> +/*
> + * Searches for a matching triplet. `va` is a pointer
> + * to the wanted commit position value. `vb` points to
> + * a triplet in lookup table. The first 4 bytes of each
> + * triplet (pointed by `vb`) are compared with `*va`.
> + */
> +static int triplet_cmp(const void *va, const void *vb)
> +{
> +
> + uint32_t a = *(uint32_t *)va;
The comment you added is definitely helpful, but I still think that this
line is a little magical. `*va` isn't really a pointer to a `uint32_t`,
but a pointer to the start of a triplet, which just *happens* to have a
4-byte integer at the beginning of it.
I don't think there's a way to improve this much more than we already
have, though. Populating a triplet struct to just dereference the first
field feels wasteful and slow. So I think what you have here makes sense
to me.
> +static uint32_t bsearch_pos(struct bitmap_index *bitmap_git,
> + struct object_id *oid,
> + uint32_t *result)
> +{
> + int found;
> +
> + if (bitmap_is_midx(bitmap_git))
> + found = bsearch_midx(oid, bitmap_git->midx, result);
> + else
> + found = bsearch_pack(oid, bitmap_git->pack, result);
> +
> + return found;
> +}
> +
> +/*
> + * `bsearch_triplet` function searches for the raw triplet having
> + * commit position same as `commit_pos` and fills `triplet`
> + * object from the raw triplet. Returns 1 on success and 0
> + * on failure.
> + */
> +static int bsearch_triplet(uint32_t *commit_pos,
> + struct bitmap_index *bitmap_git,
> + struct bitmap_lookup_table_triplet *triplet)
> +{
> + unsigned char *p = bsearch(commit_pos, bitmap_git->table_lookup, bitmap_git->entry_count,
> + BITMAP_LOOKUP_TABLE_TRIPLET_WIDTH, triplet_cmp);
> +
> + if (!p)
> + return 0;
> + triplet->commit_pos = get_be32(p);
> + p += sizeof(uint32_t);
> + triplet->offset = get_be64(p);
> + p += sizeof(uint64_t);
> + triplet->xor_row = get_be32(p);
> + return 1;
> +}
This implementation jumped out as being quite similar to
`lookup_table_get_triplet()`. Ultimately they both end up filling a
triplet struct based on some position `p` within the bitmap. The main
difference being that in `lookup_table_get_triplet()`, `p` comes from a
numeric position which indexes into the table, while in
`bsearch_triplet()` the position `p` is given to us by a call to
`bsearch()`.
I wonder if it would be worth extracting the common part of: given a
pointer `p` and a triplet struct, read the triplet beginning at `p` into
the struct.
`lookup_table_get_triplet()` could compute `p` and then return the
result of calling the new auxiliary function with that `p`. Similarly
for `bsearch_triplet()`, it would call that auxiliary function with the
pointer it got from calling `bsearch()`, or return `0` if no match was
found.
It's a minor point, but I think it would help us clean up the
implementation a little bit.
> +
> +static struct stored_bitmap *lazy_bitmap_for_commit(struct bitmap_index *bitmap_git,
> + struct commit *commit)
> +{
> + uint32_t commit_pos, xor_row;
> + uint64_t offset;
> + int flags;
> + struct bitmap_lookup_table_triplet triplet;
> + struct object_id *oid = &commit->object.oid;
> + struct ewah_bitmap *bitmap;
> + struct stored_bitmap *xor_bitmap = NULL;
> +
> + int found = bsearch_pos(bitmap_git, oid, &commit_pos);
> +
> + if (!found)
> + return NULL;
> +
> + if (!bsearch_triplet(&commit_pos, bitmap_git, &triplet))
> + return NULL;
> +
> + offset = triplet.offset;
> + xor_row = triplet.xor_row;
> +
> + if (xor_row != 0xffffffff) {
> + int xor_flags;
> + khiter_t hash_pos;
> + uint64_t offset_xor;
> + struct bitmap_lookup_table_xor_item *xor_items;
> + struct bitmap_lookup_table_xor_item xor_item;
> + size_t xor_items_nr = 0, xor_items_alloc = 64;
> +
> + ALLOC_ARRAY(xor_items, xor_items_alloc);
This ALLOC_ARRAY() looks great to me. I wonder if we could amortize the
cost of allocating in this (somewhat) hot function by treating the
`xor_items` array as a reusable static buffer where we reset
xor_items_nr to 0 when entering this function.
> + while (xor_row != 0xffffffff) {
> + struct object_id xor_oid;
> +
> + if (xor_items_nr + 1 >= bitmap_git->entry_count) {
> + free(xor_items);
> + error(_("corrupt bitmap lookup table: xor chain exceed entry count"));
I think we can probably `die()` here, we're pretty much out of luck in
this case.
> + return NULL;
> + }
> +
> + if (lookup_table_get_triplet(bitmap_git, xor_row, &triplet) < 0)
> + return NULL;
> +
> + offset_xor = triplet.offset;
> +
> + if (nth_bitmap_object_oid(bitmap_git, &xor_oid, triplet.commit_pos) < 0) {
> + free(xor_items);
> + error(_("corrupt bitmap lookup table: commit index %u out of range"),
> + triplet.commit_pos);
Same here.
> + return NULL;
> + }
> +
> + hash_pos = kh_get_oid_map(bitmap_git->bitmaps, xor_oid);
> +
> + /*
> + * If desired bitmap is already stored, we don't need
> + * to iterate further. Because we know that bitmaps
> + * that are needed to be parsed to parse this bitmap
> + * has already been stored. So, assign this stored bitmap
> + * to the xor_bitmap.
> + */
> + if (hash_pos < kh_end(bitmap_git->bitmaps) &&
> + (xor_bitmap = kh_value(bitmap_git->bitmaps, hash_pos)))
> + break;
> +
> + ALLOC_GROW(xor_items, xor_items_nr + 1, xor_items_alloc);
> + xor_items[xor_items_nr++] = (struct bitmap_lookup_table_xor_item) {.oid = xor_oid,
> + .offset = offset_xor};
This style of initialization is somewhat uncommon for Git's codebase. It
might be a little more natural to write something like:
xor_items[xor_items_nr].oid = xor_oid;
xor_items[xor_items_nr].offset = offset_xor;
xor_items_nr++;
But the struct-copying for `xor_oid` is definitely uncommon for us. We
should use the `oidcpy()` helper there instead. Or better yet, pass a
pointer to `&xor_items[xor_items_nr].oid` as the second argument to
`nth_bitmap_object_oid()` to avoid the copy altogether.
> + xor_row = triplet.xor_row;
> + }
> +
> + while (xor_items_nr) {
> + xor_item = xor_items[xor_items_nr - 1];
> + offset_xor = xor_item.offset;
> +
> + bitmap_git->map_pos = offset_xor;
> + if (bitmap_git->map_size - bitmap_git->map_pos < 6) {
Should we extract `6` out to a named constant?
Thanks,
Taylor
next prev parent reply other threads:[~2022-07-15 2:46 UTC|newest]
Thread overview: 162+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-20 12:33 [PATCH 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-06-20 12:33 ` [PATCH 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-20 16:56 ` Derrick Stolee
2022-06-20 17:09 ` Taylor Blau
2022-06-21 8:31 ` Abhradeep Chakraborty
2022-06-22 16:26 ` Taylor Blau
2022-06-21 8:23 ` Abhradeep Chakraborty
2022-06-20 17:21 ` Taylor Blau
2022-06-21 9:22 ` Abhradeep Chakraborty
2022-06-22 16:29 ` Taylor Blau
2022-06-22 16:45 ` Abhradeep Chakraborty
2022-06-20 20:21 ` Derrick Stolee
2022-06-21 10:08 ` Abhradeep Chakraborty
2022-06-22 16:30 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 2/6] pack-bitmap: prepare to read " Abhradeep Chakraborty via GitGitGadget
2022-06-20 20:49 ` Derrick Stolee
2022-06-21 10:28 ` Abhradeep Chakraborty
2022-06-20 22:06 ` Taylor Blau
2022-06-21 11:52 ` Abhradeep Chakraborty
2022-06-22 16:49 ` Taylor Blau
2022-06-22 17:18 ` Abhradeep Chakraborty
2022-06-22 21:34 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 3/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-06-20 22:16 ` Taylor Blau
2022-06-21 12:50 ` Abhradeep Chakraborty
2022-06-22 16:51 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 4/6] builtin/pack-objects.c: learn pack.writeBitmapLookupTable Taylor Blau via GitGitGadget
2022-06-20 22:18 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 5/6] bitmap-commit-table: add tests for the bitmap lookup table Abhradeep Chakraborty via GitGitGadget
2022-06-22 16:54 ` Taylor Blau
2022-06-20 12:33 ` [PATCH 6/6] bitmap-lookup-table: add performance tests Abhradeep Chakraborty via GitGitGadget
2022-06-22 17:14 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-06-26 13:10 ` [PATCH v2 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:18 ` Derrick Stolee
2022-06-27 15:48 ` Taylor Blau
2022-06-27 16:51 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:35 ` Derrick Stolee
2022-06-27 16:12 ` Taylor Blau
2022-06-27 17:10 ` Abhradeep Chakraborty
2022-06-27 16:05 ` Taylor Blau
2022-06-27 18:29 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-06-27 14:43 ` Derrick Stolee
2022-06-27 17:42 ` Abhradeep Chakraborty
2022-06-27 17:49 ` Taylor Blau
2022-06-27 17:47 ` Taylor Blau
2022-06-27 18:39 ` Abhradeep Chakraborty
2022-06-29 20:11 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-06-27 15:12 ` Derrick Stolee
2022-06-27 18:06 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table Abhradeep Chakraborty
2022-06-27 18:32 ` Derrick Stolee
2022-06-27 21:49 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Taylor Blau
2022-06-28 8:59 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table Abhradeep Chakraborty
2022-06-29 20:22 ` Taylor Blau
2022-06-30 6:58 ` [PATCH v2 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty
2022-06-27 21:38 ` Taylor Blau
2022-06-28 19:25 ` Abhradeep Chakraborty
2022-06-29 20:37 ` Taylor Blau
2022-06-29 20:41 ` Taylor Blau
2022-06-30 8:35 ` Abhradeep Chakraborty
2022-06-26 13:10 ` [PATCH v2 5/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-06-27 21:53 ` Taylor Blau
2022-06-28 7:58 ` Abhradeep Chakraborty
2022-06-29 20:40 ` Taylor Blau
2022-06-26 13:10 ` [PATCH v2 6/6] p5310-pack-bitmaps.sh: enable pack.writeReverseIndex for testing Abhradeep Chakraborty via GitGitGadget
2022-06-27 21:50 ` Taylor Blau
2022-06-28 8:01 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-07-04 8:46 ` [PATCH v3 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-08 16:38 ` Philip Oakley
2022-07-09 7:53 ` Abhradeep Chakraborty
2022-07-10 15:01 ` Philip Oakley
2022-07-14 23:15 ` Taylor Blau
2022-07-15 10:36 ` Philip Oakley
2022-07-15 18:48 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-14 23:26 ` Taylor Blau
2022-07-15 2:22 ` Taylor Blau
2022-07-15 15:58 ` Abhradeep Chakraborty
2022-07-15 22:15 ` Taylor Blau
2022-07-16 11:50 ` Abhradeep Chakraborty
2022-07-26 0:34 ` Taylor Blau
2022-07-18 8:59 ` Martin Ågren
2022-07-04 8:46 ` [PATCH v3 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-04 8:46 ` [PATCH v3 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-15 2:46 ` Taylor Blau [this message]
2022-07-15 16:38 ` Abhradeep Chakraborty
2022-07-15 22:20 ` Taylor Blau
2022-07-18 9:06 ` Martin Ågren
2022-07-18 19:25 ` Abhradeep Chakraborty
2022-07-18 23:26 ` Martin Ågren
2022-07-26 0:45 ` Taylor Blau
2022-07-04 8:46 ` [PATCH v3 5/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-07-15 2:53 ` Taylor Blau
2022-07-15 18:23 ` Abhradeep Chakraborty
2022-07-04 8:46 ` [PATCH v3 6/6] p5310-pack-bitmaps.sh: remove pack.writeReverseIndex Abhradeep Chakraborty via GitGitGadget
2022-07-04 16:35 ` [PATCH v3 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty
2022-07-06 19:21 ` Junio C Hamano
2022-07-07 8:48 ` Abhradeep Chakraborty
2022-07-07 18:09 ` Kaartic Sivaraam
2022-07-07 18:42 ` Abhradeep Chakraborty
2022-07-20 14:05 ` [PATCH v4 " Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 5/6] p5310-pack-bitmaps.sh: enable `pack.writeReverseIndex` Abhradeep Chakraborty via GitGitGadget
2022-07-20 14:05 ` [PATCH v4 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-20 18:38 ` [PATCH v5 2/6] pack-bitmap-write.c: write " Abhradeep Chakraborty via GitGitGadget
2022-07-26 0:52 ` Taylor Blau
2022-07-26 18:22 ` Abhradeep Chakraborty
2022-07-20 18:38 ` [PATCH v5 3/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-07-28 19:22 ` Johannes Schindelin
2022-08-02 12:40 ` Abhradeep Chakraborty
2022-08-02 15:35 ` Johannes Schindelin
2022-08-02 17:44 ` Abhradeep Chakraborty
2022-08-08 13:06 ` Johannes Schindelin
2022-08-08 13:58 ` Abhradeep Chakraborty
2022-08-09 9:03 ` Johannes Schindelin
2022-08-09 12:03 ` Abhradeep Chakraborty
2022-08-09 12:07 ` Abhradeep Chakraborty
2022-08-10 9:09 ` Johannes Schindelin
2022-08-10 9:20 ` Johannes Schindelin
2022-08-10 10:04 ` Abhradeep Chakraborty
2022-08-10 17:51 ` Derrick Stolee
2022-08-12 18:51 ` Abhradeep Chakraborty
2022-08-12 19:22 ` Derrick Stolee
2022-08-13 10:59 ` Abhradeep Chakraborty
2022-08-16 21:57 ` Taylor Blau
2022-08-17 10:02 ` Abhradeep Chakraborty
2022-08-17 20:38 ` Taylor Blau
2022-08-19 21:49 ` Taylor Blau
2022-08-13 11:05 ` Abhradeep Chakraborty
2022-08-16 18:47 ` Taylor Blau
2022-07-20 18:38 ` [PATCH v5 4/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-07-26 1:13 ` Taylor Blau
2022-07-26 18:56 ` Abhradeep Chakraborty
2022-07-26 19:36 ` Eric Sunshine
2022-07-20 18:38 ` [PATCH v5 5/6] p5310-pack-bitmaps.sh: enable `pack.writeReverseIndex` Abhradeep Chakraborty via GitGitGadget
2022-07-26 1:18 ` Taylor Blau
2022-07-26 7:15 ` Ævar Arnfjörð Bjarmason
2022-07-26 13:32 ` Derrick Stolee
2022-07-26 13:54 ` Ævar Arnfjörð Bjarmason
2022-07-26 18:17 ` Abhradeep Chakraborty
2022-07-20 18:38 ` [PATCH v5 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 1/6] Documentation/technical: describe bitmap lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 2/6] bitmap: move `get commit positions` code to `bitmap_writer_finish` Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 3/6] pack-bitmap-write.c: write lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 4/6] pack-bitmap-write: learn pack.writeBitmapLookupTable and add tests Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 5/6] pack-bitmap: prepare to read lookup table extension Abhradeep Chakraborty via GitGitGadget
2022-08-14 16:55 ` [PATCH v6 6/6] bitmap-lookup-table: add performance tests for lookup table Abhradeep Chakraborty via GitGitGadget
2022-08-19 21:21 ` [PATCH v6 0/6] [GSoC] bitmap: integrate a lookup table extension to the bitmap format Junio C Hamano
2022-08-22 14:42 ` Johannes Schindelin
2022-08-22 14:48 ` Taylor Blau
2022-08-25 22:16 ` Taylor Blau
2022-08-26 16:02 ` Junio C Hamano
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