Re: Re: O_DIRECT to md raid 6 is slow

[kedacomkernel <kedacomkernel@gmail.com>]

On 2012-08-15 09:12 Andy Lutomirski <luto@amacapital.net> Wrote:
>Ubuntu's 3.2.0-27-generic.  I can test on a newer kernel tomorrow.
I guess maybe miss the blk_plug function.
Can you add this patch and retest.

Move unplugging for direct I/O from around ->direct_IO() down to
do_blockdev_direct_IO(). This implicitly adds plugging for direct
writes.
 
CC: Li Shaohua <shli@fusionio.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 fs/direct-io.c |    5 +++++
 mm/filemap.c   |    4 ----
 2 files changed, 5 insertions(+), 4 deletions(-)
 
--- linux-next.orig/mm/filemap.c 2012-08-05 16:24:47.859465122 +0800
+++ linux-next/mm/filemap.c 2012-08-05 16:24:48.407465135 +0800
@@ -1412,12 +1412,8 @@ generic_file_aio_read(struct kiocb *iocb
  retval = filemap_write_and_wait_range(mapping, pos,
  pos + iov_length(iov, nr_segs) - 1);
  if (!retval) {
- struct blk_plug plug;
-
- blk_start_plug(&plug);
  retval = mapping->a_ops->direct_IO(READ, iocb,
  iov, pos, nr_segs);
- blk_finish_plug(&plug);
  }
  if (retval > 0) {
  *ppos = pos + retval;
--- linux-next.orig/fs/direct-io.c 2012-07-07 21:46:39.531508198 +0800
+++ linux-next/fs/direct-io.c 2012-08-05 16:24:48.411465136 +0800
@@ -1062,6 +1062,7 @@ do_blockdev_direct_IO(int rw, struct kio
  unsigned long user_addr;
  size_t bytes;
  struct buffer_head map_bh = { 0, };
+ struct blk_plug plug;
 
  if (rw & WRITE)
  rw = WRITE_ODIRECT;
@@ -1177,6 +1178,8 @@ do_blockdev_direct_IO(int rw, struct kio
  PAGE_SIZE - user_addr / PAGE_SIZE);
  }
 
+ blk_start_plug(&plug);
+
  for (seg = 0; seg < nr_segs; seg++) {
  user_addr = (unsigned long)iov[seg].iov_base;
  sdio.size += bytes = iov[seg].iov_len;
@@ -1235,6 +1238,8 @@ do_blockdev_direct_IO(int rw, struct kio
  if (sdio.bio)
  dio_bio_submit(dio, &sdio);
 
+ blk_finish_plug(&plug);
+
  /*
   * It is possible that, we return short IO due to end of file.
   * In that case, we need to release all the pages we got hold on.
 
 
--