Btrfs: Fix streaming read performance with checksumming on
Large streaming reads make for large bios, which means each entry on the
list async work queues represents a large amount of data. IO
congestion throttling on the device was kicking in before the async
worker threads decided a single thread was busy and needed some help.
The end result was that a streaming read would result in a single CPU
running at 100% instead of balancing the work off to other CPUs.
This patch also changes the pre-IO checksum lookup done by reads to
work on a per-bio basis instead of a per-page. This results in many
extra btree lookups on large streaming reads. Doing the checksum lookup
right before bio submit allows us to reuse searches while processing
adjacent offsets.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index e826730..d2d1cc8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1357,10 +1357,25 @@
*/
btrfs_init_workers(&fs_info->workers, fs_info->thread_pool_size);
btrfs_init_workers(&fs_info->submit_workers, fs_info->thread_pool_size);
+
+ /* a higher idle thresh on the submit workers makes it much more
+ * likely that bios will be send down in a sane order to the
+ * devices
+ */
+ fs_info->submit_workers.idle_thresh = 64;
+
btrfs_init_workers(&fs_info->fixup_workers, 1);
btrfs_init_workers(&fs_info->endio_workers, fs_info->thread_pool_size);
btrfs_init_workers(&fs_info->endio_write_workers,
fs_info->thread_pool_size);
+
+ /*
+ * endios are largely parallel and should have a very
+ * low idle thresh
+ */
+ fs_info->endio_workers.idle_thresh = 4;
+ fs_info->endio_write_workers.idle_thresh = 4;
+
btrfs_start_workers(&fs_info->workers, 1);
btrfs_start_workers(&fs_info->submit_workers, 1);
btrfs_start_workers(&fs_info->fixup_workers, 1);
