From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f49.google.com ([74.125.82.49]:54709 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755302Ab3H2Mpo (ORCPT ); Thu, 29 Aug 2013 08:45:44 -0400 Received: by mail-wg0-f49.google.com with SMTP id a12so372093wgh.16 for ; Thu, 29 Aug 2013 05:45:43 -0700 (PDT) From: Filipe David Borba Manana To: linux-btrfs@vger.kernel.org Cc: sbehrens@giantdisaster.de, Filipe David Borba Manana Subject: [PATCH] Btrfs: optimize key searches in btrfs_search_slot Date: Thu, 29 Aug 2013 13:44:13 +0100 Message-Id: <1377780253-17826-1-git-send-email-fdmanana@gmail.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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: 5013 Range: 25.000 - 497.000; Mean: 82.767; Median: 64.000; Stddev: 49.972 Percentiles: 90th: 141.000; 95th: 182.000; 99th: 287.000 25.000 - 33.930: 211 ###### 33.930 - 45.927: 277 ######## 45.927 - 62.045: 1834 ##################################################### 62.045 - 83.699: 1203 ################################### 83.699 - 112.789: 609 ################## 112.789 - 151.872: 450 ############# 151.872 - 204.377: 246 ####### 204.377 - 274.917: 124 #### 274.917 - 369.684: 48 # 369.684 - 497.000: 11 | Approach proposed by this patch: Count: 5013 Range: 10.000 - 8303.000; Mean: 28.505; Median: 18.000; Stddev: 119.147 Percentiles: 90th: 49.000; 95th: 74.000; 99th: 115.000 10.000 - 20.339: 3160 ##################################################### 20.339 - 40.397: 1131 ################### 40.397 - 79.308: 507 ######### 79.308 - 154.794: 199 ### 154.794 - 301.232: 14 | 301.232 - 585.313: 1 | 585.313 - 8303.000: 1 | 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 --- fs/btrfs/ctree.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 59 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 5fa521b..5b20eec 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2426,6 +2426,59 @@ done: return ret; } +static int key_search(struct extent_buffer *b, struct btrfs_key *key, + int level, int *prev_cmp, int *slot) +{ + unsigned long eb_offset = 0; + unsigned long len_left = b->len; + char *kaddr = NULL; + unsigned long map_start = 0; + unsigned long map_len = 0; + unsigned long offset; + struct btrfs_disk_key *k = NULL; + struct btrfs_disk_key unaligned; + + if (*prev_cmp != 0) { + *prev_cmp = bin_search(b, key, level, slot); + return *prev_cmp; + } + + if (level == 0) + offset = offsetof(struct btrfs_leaf, items); + else + offset = offsetof(struct btrfs_node, ptrs); + + /* + * Map the entire extent buffer, otherwise callers can't access + * all keys/items of the leaf/node. Specially needed for case + * where leaf/node size is greater than page cache size. + */ + while (len_left > 0) { + unsigned long len = min(PAGE_CACHE_SIZE, len_left); + int err; + + err = map_private_extent_buffer(b, eb_offset, len, &kaddr, + &map_start, &map_len); + len_left -= len; + eb_offset += len; + if (k) + continue; + if (!err) { + k = (struct btrfs_disk_key *)(kaddr + offset - + map_start); + } else { + read_extent_buffer(b, &unaligned, + offset, sizeof(unaligned)); + k = &unaligned; + } + } + + BUG_ON(comp_keys(k, key) != 0); + *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 +2507,7 @@ 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 +2538,7 @@ 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 +2639,7 @@ 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 +2774,7 @@ 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 +2785,7 @@ 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 +2803,7 @@ 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; -- 1.7.9.5