Some initial probe requests don't have disk->queue mapped yet, so we
can't rely on a non-NULL queue in blk_queue_io_stat(). Wrap it in
blk_do_io_stat().

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

This allows us to turn off disk stat accounting completely, for the cases
where the 0.5-1% reduction in system time is important.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

This fixes a "regression" from 2.6.28, where the barrier probes that file
systems may do would trigger additional end request warnings in dmesg.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

We just want to hand the first bits of IO to the device as fast
as possible. Gains a few percent on the IOPS rate.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

* Because barrier mode can be changed dynamically, whether barrier is
  supported or not can be determined only when actually issuing the
  barrier and there is no point in checking it earlier.  Drop barrier
  support check in generic_make_request() and __make_request(), and
  update comment around the support check in blk_do_ordered().

* There is no reason to check discard support in both
  generic_make_request() and __make_request().  Drop the check in
  __make_request().  While at it, move error action block to the end
  of the function and add unlikely() to q existence test.

* Barrier request, be it empty or not, is never passed to low level
  driver and thus it's meaningless to try to copy back req->sector to
  bio->bi_sector on error.  In addition, the notion of failed sector
  doesn't make any sense for empty barrier to begin with.  Drop the
  code block from __end_that_request_first().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

After many improvements on kblockd_flush_work, it is now identical to
cancel_work_sync, so a direct call to cancel_work_sync is suggested.

The only difference is that cancel_work_sync is a GPL symbol,
so no non-GPL modules anymore.

Signed-off-by: Cheng Renquan <crquan@gmail.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

Allow the scsi request REQ_QUIET flag to be propagated to the buffer
file system layer. The basic ideas is to pass the flag from the scsi
request to the bio (block IO) and then to the buffer layer.  The buffer
layer can then suppress needless printks.

This patch declutters the kernel log by removed the 40-50 (per lun)
buffer io error messages seen during a boot in my multipath setup . It
is a good chance any real errors will be missed in the "noise" it the
logs without this patch.

During boot I see blocks of messages like
"
__ratelimit: 211 callbacks suppressed
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242847
Buffer I/O error on device sdm, logical block 1
Buffer I/O error on device sdm, logical block 5242878
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242879
Buffer I/O error on device sdm, logical block 5242872
"
in my logs.

My disk environment is multipath fiber channel using the SCSI_DH_RDAC
code and multipathd.  This topology includes an "active" and "ghost"
path for each lun. IO's to the "ghost" path will never complete and the
SCSI layer, via the scsi device handler rdac code, quick returns the IOs
to theses paths and sets the REQ_QUIET scsi flag to suppress the scsi
layer messages.

 I am wanting to extend the QUIET behavior to include the buffer file
system layer to deal with these errors as well. I have been running this
patch for a while now on several boxes without issue.  A few runs of
bonnie++ show no noticeable difference in performance in my setup.

Thanks for John Stultz for the quiet_error finalization.

Submitted-by:  Keith Mannthey <kmannth@us.ibm.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

For sync IO, we'll often do them serialized. This means we'll be touching
the queue timer for every IO, as opposed to only occasionally like we
do for queued IO. Instead of deleting the timer when the last request
is removed, just let continue running. If a new request comes up soon
we then don't have to readd the timer again. If no new requests arrive,
the timer will expire without side effect later.

This improves high iops sync IO by ~1%.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>