Our current handling of direct I/O completions is rather suboptimal,
because we defer it to a workqueue more often than needed, and we
perform a much to aggressive flush of the workqueue in case unwritten
extent conversions happen.
This patch changes the direct I/O reads to not even use a completion
handler, as we don't bother to use it at all, and to perform the unwritten
extent conversions in caller context for synchronous direct I/O.
For a small I/O size direct I/O workload on a consumer grade SSD, such as
the untar of a kernel tree inside qemu this patch gives speedups of
about 5%. Getting us much closer to the speed of a native block device,
or a fully allocated XFS file.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: xfs/fs/xfs/linux-2.6/xfs_aops.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_aops.c 2010-07-18 22:41:48.896494681 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_aops.c 2010-07-18 22:46:52.366494681 +0200
@@ -202,23 +202,17 @@ xfs_setfilesize(
}
/*
- * Schedule IO completion handling on a xfsdatad if this was
- * the final hold on this ioend. If we are asked to wait,
- * flush the workqueue.
+ * Schedule IO completion handling on the final put of an ioend.
*/
STATIC void
xfs_finish_ioend(
- xfs_ioend_t *ioend,
- int wait)
+ struct xfs_ioend *ioend)
{
if (atomic_dec_and_test(&ioend->io_remaining)) {
- struct workqueue_struct *wq;
-
- wq = (ioend->io_type == IO_UNWRITTEN) ?
- xfsconvertd_workqueue : xfsdatad_workqueue;
- queue_work(wq, &ioend->io_work);
- if (wait)
- flush_workqueue(wq);
+ if (ioend->io_type == IO_UNWRITTEN)
+ queue_work(xfsconvertd_workqueue, &ioend->io_work);
+ else
+ queue_work(xfsdatad_workqueue, &ioend->io_work);
}
}
@@ -262,7 +256,7 @@ xfs_end_io(
*/
if (error == EAGAIN) {
atomic_inc(&ioend->io_remaining);
- xfs_finish_ioend(ioend, 0);
+ xfs_finish_ioend(ioend);
/* ensure we don't spin on blocked ioends */
delay(1);
} else {
@@ -273,6 +267,17 @@ xfs_end_io(
}
/*
+ * Call IO completion handling in caller context on the final put of an ioend.
+ */
+STATIC void
+xfs_finish_ioend_sync(
+ struct xfs_ioend *ioend)
+{
+ if (atomic_dec_and_test(&ioend->io_remaining))
+ xfs_end_io(&ioend->io_work);
+}
+
+/*
* Allocate and initialise an IO completion structure.
* We need to track unwritten extent write completion here initially.
* We'll need to extend this for updating the ondisk inode size later
@@ -353,7 +358,7 @@ xfs_end_bio(
bio->bi_end_io = NULL;
bio_put(bio);
- xfs_finish_ioend(ioend, 0);
+ xfs_finish_ioend(ioend);
}
STATIC void
@@ -495,7 +500,7 @@ xfs_submit_ioend(
}
if (bio)
xfs_submit_ioend_bio(wbc, ioend, bio);
- xfs_finish_ioend(ioend, 0);
+ xfs_finish_ioend(ioend);
} while ((ioend = next) != NULL);
}
@@ -1406,70 +1411,56 @@ xfs_get_blocks_direct(
return __xfs_get_blocks(inode, iblock, bh_result, create, 1);
}
+/*
+ * Complete a direct I/O write request.
+ *
+ * If the private argument is non-NULL __xfs_get_blocks signals us that we
+ * need to issue a transaction to convert the range from unwritten to written
+ * extents. In case this is regular synchronous I/O we just call xfs_end_io
+ * to do this and we are done. But in case this was a successfull AIO
+ * request this handler is called from interrupt context, from which we
+ * can't start transactions. In that case offload the I/O completion to
+ * the workqueues we also use for buffered I/O completion.
+ */
STATIC void
-xfs_end_io_direct(
- struct kiocb *iocb,
- loff_t offset,
- ssize_t size,
- void *private,
- int ret,
- bool is_async)
+xfs_end_io_direct_write(
+ struct kiocb *iocb,
+ loff_t offset,
+ ssize_t size,
+ void *private,
+ int ret,
+ bool is_async)
{
- xfs_ioend_t *ioend = iocb->private;
- bool complete_aio = is_async;
+ struct xfs_ioend *ioend = iocb->private;
/*
- * Non-NULL private data means we need to issue a transaction to
- * convert a range from unwritten to written extents. This needs
- * to happen from process context but aio+dio I/O completion
- * happens from irq context so we need to defer it to a workqueue.
- * This is not necessary for synchronous direct I/O, but we do
- * it anyway to keep the code uniform and simpler.
- *
- * Well, if only it were that simple. Because synchronous direct I/O
- * requires extent conversion to occur *before* we return to userspace,
- * we have to wait for extent conversion to complete. Look at the
- * iocb that has been passed to us to determine if this is AIO or
- * not. If it is synchronous, tell xfs_finish_ioend() to kick the
- * workqueue and wait for it to complete.
- *
- * The core direct I/O code might be changed to always call the
- * completion handler in the future, in which case all this can
- * go away.
+ * blockdev_direct_IO can return an error even after the I/O
+ * completion handler was called. Thus we need to protect
+ * against double-freeing.
*/
+ iocb->private = NULL;
+
ioend->io_offset = offset;
ioend->io_size = size;
- if (ioend->io_type == IO_READ) {
- xfs_finish_ioend(ioend, 0);
- } else if (private && size > 0) {
- if (is_async) {
+ if (private && size > 0)
+ ioend->io_type = IO_UNWRITTEN;
+
+ if (is_async) {
+ /*
+ * If we are converting an unwritten extent we need to delay
+ * the AIO completion until after the unwrittent extent
+ * conversion has completed, otherwise do it ASAP.
+ */
+ if (ioend->io_type == IO_UNWRITTEN) {
ioend->io_iocb = iocb;
ioend->io_result = ret;
- complete_aio = false;
- xfs_finish_ioend(ioend, 0);
} else {
- xfs_finish_ioend(ioend, 1);
+ aio_complete(iocb, ret, 0);
}
+ xfs_finish_ioend(ioend);
} else {
- /*
- * A direct I/O write ioend starts it's life in unwritten
- * state in case they map an unwritten extent. This write
- * didn't map an unwritten extent so switch it's completion
- * handler.
- */
- ioend->io_type = IO_NEW;
- xfs_finish_ioend(ioend, 0);
+ xfs_finish_ioend_sync(ioend);
}
-
- /*
- * blockdev_direct_IO can return an error even after the I/O
- * completion handler was called. Thus we need to protect
- * against double-freeing.
- */
- iocb->private = NULL;
-
- if (complete_aio)
- aio_complete(iocb, ret, 0);
}
STATIC ssize_t
@@ -1480,23 +1471,26 @@ xfs_vm_direct_IO(
loff_t offset,
unsigned long nr_segs)
{
- struct file *file = iocb->ki_filp;
- struct inode *inode = file->f_mapping->host;
- struct block_device *bdev;
- ssize_t ret;
-
- bdev = xfs_find_bdev_for_inode(inode);
-
- iocb->private = xfs_alloc_ioend(inode, rw == WRITE ?
- IO_UNWRITTEN : IO_READ);
-
- ret = blockdev_direct_IO_no_locking(rw, iocb, inode, bdev, iov,
- offset, nr_segs,
- xfs_get_blocks_direct,
- xfs_end_io_direct);
+ struct inode *inode = iocb->ki_filp->f_mapping->host;
+ struct block_device *bdev = xfs_find_bdev_for_inode(inode);
+ ssize_t ret;
+
+ if (rw & WRITE) {
+ iocb->private = xfs_alloc_ioend(inode, IO_NEW);
+
+ ret = blockdev_direct_IO_no_locking(rw, iocb, inode, bdev, iov,
+ offset, nr_segs,
+ xfs_get_blocks_direct,
+ xfs_end_io_direct_write);
+ if (ret != -EIOCBQUEUED && iocb->private)
+ xfs_destroy_ioend(iocb->private);
+ } else {
+ ret = blockdev_direct_IO_no_locking(rw, iocb, inode, bdev, iov,
+ offset, nr_segs,
+ xfs_get_blocks_direct,
+ NULL);
+ }
- if (unlikely(ret != -EIOCBQUEUED && iocb->private))
- xfs_destroy_ioend(iocb->private);
return ret;
}
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