Re: [Regression 3.16-rc kernel] -55% reduction in throughput for OLTP benchmark

From: Christoph Hellwig
Date: Tue Jul 29 2014 - 12:50:04 EST


On Tue, Jul 29, 2014 at 09:35:02AM -0700, Tim Chen wrote:
> On Tue, 2014-07-29 at 07:19 -0700, Christoph Hellwig wrote:
> > Hi Tim,
> >
> > I think the problem is that sdio.size doesn't get set set with
> > the new dio code. Please try the patch below to fix this by not
> > relying on that field:
>
> Thanks for your quick response. We'll test this patch and let you
> know the results.

There actually was a little bug in it, please try the version below
instead:


diff --git a/fs/direct-io.c b/fs/direct-io.c
index 194d0d1..17e39b0 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -71,7 +71,6 @@ struct dio_submit {
been performed at the start of a
write */
int pages_in_io; /* approximate total IO pages */
- size_t size; /* total request size (doesn't change)*/
sector_t block_in_file; /* Current offset into the underlying
file in dio_block units. */
unsigned blocks_available; /* At block_in_file. changes */
@@ -1104,7 +1103,8 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
unsigned blkbits = i_blkbits;
unsigned blocksize_mask = (1 << blkbits) - 1;
ssize_t retval = -EINVAL;
- loff_t end = offset + iov_iter_count(iter);
+ size_t count = iov_iter_count(iter);
+ loff_t end = offset + count;
struct dio *dio;
struct dio_submit sdio = { 0, };
struct buffer_head map_bh = { 0, };
@@ -1287,10 +1287,9 @@ do_blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
*/
BUG_ON(retval == -EIOCBQUEUED);
if (dio->is_async && retval == 0 && dio->result &&
- ((rw == READ) || (dio->result == sdio.size)))
+ (rw == READ || dio->result == count))
retval = -EIOCBQUEUED;
-
- if (retval != -EIOCBQUEUED)
+ else
dio_await_completion(dio);

if (drop_refcount(dio) == 0) {
--
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