| Message ID | 1377874003-19188-1-git-send-email-fdmanana@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On fri, 30 Aug 2013 15:46:43 +0100, Filipe David Borba Manana wrote: > 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> > --- > > V2: Simplified code, removed unnecessary code. > V3: Replaced BUG_ON() with the new ASSERT() from Josef. > V4: Addressed latest comments from Zach Brown and Josef Bacik. > Surrounded all code that is used for the assertion with a > #ifdef CONFIG_BTRFS_ASSERT ... #endif block. Also changed > offset arguments to be more strictly correct. > V5: Updated histograms to reflect latest version of the code. > > fs/btrfs/ctree.c | 42 ++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 40 insertions(+), 2 deletions(-) > > diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c > index 5fa521b..6434672 100644 > --- a/fs/btrfs/ctree.c > +++ b/fs/btrfs/ctree.c > @@ -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 > +} I think it is better to move #ifdef out of key_search_validate(), and make the function return the check result, then > + > +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); ASSERT(key_search_validate(b, key, level)); it can make the compiler happen when CONFIG_BTRFS_ASSERT is not set. Thanks Miao > + *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; > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 5fa521b..6434672 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -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;
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> --- V2: Simplified code, removed unnecessary code. V3: Replaced BUG_ON() with the new ASSERT() from Josef. V4: Addressed latest comments from Zach Brown and Josef Bacik. Surrounded all code that is used for the assertion with a #ifdef CONFIG_BTRFS_ASSERT ... #endif block. Also changed offset arguments to be more strictly correct. V5: Updated histograms to reflect latest version of the code. fs/btrfs/ctree.c | 42 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 40 insertions(+), 2 deletions(-)