Btrfs: Lower contention on the csum mutex

This takes the csum mutex deeper in the call chain and releases it
more often.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

4 files changed, 22 insertions, 8 deletions

diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 958cd8b5f0d7..2ee301740195 100644
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -48,6 +48,7 @@ struct btrfs_worker_thread {
 
         /* number of things on the pending list */
         atomic_t num_pending;
+
         unsigned long sequence;
 
         /* protects the pending list. */
@@ -242,7 +243,7 @@ static struct btrfs_worker_thread *next_worker(struct btrfs_workers *workers)
         worker = list_entry(next, struct btrfs_worker_thread, worker_list);
         atomic_inc(&worker->num_pending);
         worker->sequence++;
-        if (worker->sequence % 4 == 0)
+        if (worker->sequence % workers->idle_thresh == 0)
                 list_move_tail(next, &workers->worker_list);
         return worker;
 }
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1aed1f4616b6..92e14dd9bddb 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1386,7 +1386,14 @@ struct btrfs_root *open_ctree(struct super_block *sb,
          * devices
          */
         fs_info->submit_workers.idle_thresh = 64;
-        fs_info->workers.idle_thresh = 32;
+
+        /* fs_info->workers is responsible for checksumming file data
+         * blocks and metadata.  Using a larger idle thresh allows each
+         * worker thread to operate on things in roughly the order they
+         * were sent by the writeback daemons, improving overall locality
+         * of the IO going down the pipe.
+         */
+        fs_info->workers.idle_thresh = 128;
 
         btrfs_init_workers(&fs_info->fixup_workers, "fixup", 1);
         btrfs_init_workers(&fs_info->endio_workers, "endio",
diff --git a/fs/btrfs/file-item.c b/fs/btrfs/file-item.c
index 51aba8cee7ce..9454e0a07c89 100644
--- a/fs/btrfs/file-item.c
+++ b/fs/btrfs/file-item.c
@@ -321,6 +321,7 @@ again:
         file_key.offset = offset;
         btrfs_set_key_type(&file_key, BTRFS_CSUM_ITEM_KEY);
 
+        mutex_lock(&BTRFS_I(inode)->csum_mutex);
         item = btrfs_lookup_csum(trans, root, path, objectid, offset, 1);
         if (!IS_ERR(item)) {
                 leaf = path->nodes[0];
@@ -367,7 +368,7 @@ again:
         ret = btrfs_search_slot(trans, root, &file_key, path,
                                 BTRFS_CRC32_SIZE, 1);
         if (ret < 0)
-                goto fail;
+                goto fail_unlock;
         if (ret == 0) {
                 BUG();
         }
@@ -411,10 +412,10 @@ insert:
         ret = btrfs_insert_empty_item(trans, root, path, &file_key,
                                       ins_size);
         if (ret < 0)
-                goto fail;
+                goto fail_unlock;
         if (ret != 0) {
                 WARN_ON(1);
-                goto fail;
+                goto fail_unlock;
         }
 csum:
         leaf = path->nodes[0];
@@ -427,6 +428,8 @@ found:
         item_end = (struct btrfs_csum_item *)((unsigned char *)item_end +
                                       btrfs_item_size_nr(leaf, path->slots[0]));
         eb_token = NULL;
+        mutex_unlock(&BTRFS_I(inode)->csum_mutex);
+        cond_resched();
 next_sector:
 
         if (!eb_token ||
@@ -467,13 +470,18 @@ next_sector:
                 eb_token = NULL;
         }
         btrfs_mark_buffer_dirty(path->nodes[0]);
+        cond_resched();
         if (total_bytes < sums->len) {
                 btrfs_release_path(root, path);
                 goto again;
         }
-fail:
+out:
         btrfs_free_path(path);
         return ret;
+
+fail_unlock:
+        mutex_unlock(&BTRFS_I(inode)->csum_mutex);
+        goto out;
 }
 
 int btrfs_csum_truncate(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 33b990878d84..65107894a5bb 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -415,10 +415,8 @@ static noinline int add_pending_csums(struct btrfs_trans_handle *trans,
         btrfs_set_trans_block_group(trans, inode);
         list_for_each(cur, list) {
                 sum = list_entry(cur, struct btrfs_ordered_sum, list);
-                mutex_lock(&BTRFS_I(inode)->csum_mutex);
                 btrfs_csum_file_blocks(trans, BTRFS_I(inode)->root,
                                        inode, sum);
-                mutex_unlock(&BTRFS_I(inode)->csum_mutex);
         }
         return 0;
 }