Btrfs: optimize key searches in btrfs_search_slot (d7396f07) · Commits · 戴 / test

When the binary search returns 0 (exact match), the target key will necessarily be at slot 0 of all nodes below the current one, so in this case the binary search is not needed because it will always return 0, and we waste time doing it, holding node locks for longer than necessary, etc. Below follow histograms with the times spent on the current approach of doing a binary search when the previous binary search returned 0, and times for the new approach, which directly picks the first item/child node in the leaf/node. Current approach: Count: 6682 Range: 35.000 - 8370.000; Mean: 85.837; Median: 75.000; Stddev: 106.429 Percentiles: 90th: 124.000; 95th: 145.000; 99th: 206.000 35.000 - 61.080: 1235 ################ 61.080 - 106.053: 4207 ##################################################### 106.053 - 183.606: 1122 ############## 183.606 - 317.341: 111 # 317.341 - 547.959: 6 | 547.959 - 8370.000: 1 | Approach proposed by this patch: Count: 6682 Range: 6.000 - 135.000; Mean: 16.690; Median: 16.000; Stddev: 7.160 Percentiles: 90th: 23.000; 95th: 27.000; 99th: 40.000 6.000 - 8.418: 58 # 8.418 - 11.670: 1149 ######################### 11.670 - 16.046: 2418 ##################################################### 16.046 - 21.934: 2098 ############################################## 21.934 - 29.854: 744 ################ 29.854 - 40.511: 154 ### 40.511 - 54.848: 41 # 54.848 - 74.136: 5 | 74.136 - 100.087: 9 | 100.087 - 135.000: 6 | These samples were captured during a run of the btrfs tests 001, 002 and 004 in the xfstests, with a leaf/node size of 4Kb. Signed-off-by:

Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by:

Josef Bacik <jbacik@fusionio.com> Signed-off-by:

Chris Mason <chris.mason@fusionio.com>

fs/btrfs/ctree.c

+40 −2

Original line number	Diff line number	Diff line
		@@ -2426,6 +2426,40 @@ done:
		return ret;
		}

		static void key_search_validate(struct extent_buffer *b,
		struct btrfs_key *key,
		int level)
		{
		#ifdef CONFIG_BTRFS_ASSERT
		struct btrfs_disk_key disk_key;

		btrfs_cpu_key_to_disk(&disk_key, key);

		if (level == 0)
		ASSERT(!memcmp_extent_buffer(b, &disk_key,
		offsetof(struct btrfs_leaf, items[0].key),
		sizeof(disk_key)));
		else
		ASSERT(!memcmp_extent_buffer(b, &disk_key,
		offsetof(struct btrfs_node, ptrs[0].key),
		sizeof(disk_key)));
		#endif
		}

		static int key_search(struct extent_buffer b, struct btrfs_key key,
		int level, int prev_cmp, int slot)
		{
		if (*prev_cmp != 0) {
		*prev_cmp = bin_search(b, key, level, slot);
		return *prev_cmp;
		}

		key_search_validate(b, key, level);
		*slot = 0;

		return 0;
		}

		/*
		* look for key in the tree. path is filled in with nodes along the way
		* if key is found, we return zero and you can find the item in the leaf
		@@ -2454,6 +2488,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
		int write_lock_level = 0;
		u8 lowest_level = 0;
		int min_write_lock_level;
		int prev_cmp;

		lowest_level = p->lowest_level;
		WARN_ON(lowest_level && ins_len > 0);
		@@ -2484,6 +2519,7 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root
		min_write_lock_level = write_lock_level;

		again:
		prev_cmp = -1;
		/*
		* we try very hard to do read locks on the root
		*/
		@@ -2584,7 +2620,7 @@ cow_done:
		if (!cow)
		btrfs_unlock_up_safe(p, level + 1);

		ret = bin_search(b, key, level, &slot);
		ret = key_search(b, key, level, &prev_cmp, &slot);

		if (level != 0) {
		int dec = 0;
		@@ -2719,6 +2755,7 @@ int btrfs_search_old_slot(struct btrfs_root root, struct btrfs_key key,
		int level;
		int lowest_unlock = 1;
		u8 lowest_level = 0;
		int prev_cmp;

		lowest_level = p->lowest_level;
		WARN_ON(p->nodes[0] != NULL);
		@@ -2729,6 +2766,7 @@ int btrfs_search_old_slot(struct btrfs_root root, struct btrfs_key key,
		}

		again:
		prev_cmp = -1;
		b = get_old_root(root, time_seq);
		level = btrfs_header_level(b);
		p->locks[level] = BTRFS_READ_LOCK;
		@@ -2746,7 +2784,7 @@ again:
		*/
		btrfs_unlock_up_safe(p, level + 1);

		ret = bin_search(b, key, level, &slot);
		ret = key_search(b, key, level, &prev_cmp, &slot);

		if (level != 0) {
		int dec = 0;

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