From bedf762ba3a4b70295661fa70c29c1f18fe0f351 Mon Sep 17 00:00:00 2001 From: Chris Mason Date: Fri, 3 Apr 2009 10:32:58 -0400 Subject: [PATCH] Btrfs: unplug in the async bio submission threads Btrfs pages being written get set to writeback, and then may go through a number of steps before they hit the block layer. This includes compression, checksumming and async bio submission. The end result is that someone who writes a page and then does wait_on_page_writeback is likely to unplug the queue before the bio they cared about got there. We could fix this by marking bios sync, or by doing more frequent unplugs, but this commit just changes the async bio submission code to unplug after it has processed all the bios for a device. The async bio submission does a fair job of collection bios, so this shouldn't be a huge problem for reducing merging at the elevator. For streaming O_DIRECT writes on a 5 drive array, it boosts performance from 386MB/s to 460MB/s. Thanks to Hisashi Hifumi for helping with this work. Signed-off-by: Chris Mason --- fs/btrfs/volumes.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index cc01abff03d..e0913e46972 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -148,7 +148,7 @@ static noinline int run_scheduled_bios(struct btrfs_device *device) unsigned long limit; unsigned long last_waited = 0; - bdi = device->bdev->bd_inode->i_mapping->backing_dev_info; + bdi = blk_get_backing_dev_info(device->bdev); fs_info = device->dev_root->fs_info; limit = btrfs_async_submit_limit(fs_info); limit = limit * 2 / 3; @@ -258,6 +258,18 @@ loop_lock: if (device->pending_bios) goto loop_lock; spin_unlock(&device->io_lock); + + /* + * IO has already been through a long path to get here. Checksumming, + * async helper threads, perhaps compression. We've done a pretty + * good job of collecting a batch of IO and should just unplug + * the device right away. + * + * This will help anyone who is waiting on the IO, they might have + * already unplugged, but managed to do so before the bio they + * cared about found its way down here. + */ + blk_run_backing_dev(bdi, NULL); done: return 0; } -- 2.32.0.93.g670b81a890