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From: Tejun Heo on 12 Aug 2010 08:50
Nobody is making meaningful use of ORDERED_BY_TAG now and queue
draining for barrier requests will be removed soon which will render
the advantage of tag ordering moot. Kill ORDERED_BY_TAG. The
following users are affected.

* brd: converted to ORDERED_DRAIN.
* virtio_blk: ORDERED_TAG path was already marked deprecated. Removed.
* xen-blkfront: ORDERED_TAG case dropped.

Signed-off-by: Tejun Heo <tj(a)kernel.org>
Cc: Christoph Hellwig <hch(a)infradead.org>
Cc: Nick Piggin <npiggin(a)kernel.dk>
Cc: Michael S. Tsirkin <mst(a)redhat.com>
Cc: Jeremy Fitzhardinge <jeremy(a)xensource.com>
Cc: Chris Wright <chrisw(a)sous-sol.org>
---
block/blk-barrier.c | 35 +++++++----------------------------
drivers/block/brd.c | 2 +-
drivers/block/virtio_blk.c | 9 ---------
drivers/block/xen-blkfront.c | 8 +++-----
drivers/scsi/sd.c | 4 +---
include/linux/blkdev.h | 17 +----------------
6 files changed, 13 insertions(+), 62 deletions(-)

diff --git a/block/blk-barrier.c b/block/blk-barrier.c
index f0faefc..c807e9c 100644
--- a/block/blk-barrier.c
+++ b/block/blk-barrier.c
@@ -26,10 +26,7 @@ int blk_queue_ordered(struct request_queue *q, unsigned ordered)
if (ordered != QUEUE_ORDERED_NONE &&
ordered != QUEUE_ORDERED_DRAIN &&
ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
- ordered != QUEUE_ORDERED_DRAIN_FUA &&
- ordered != QUEUE_ORDERED_TAG &&
- ordered != QUEUE_ORDERED_TAG_FLUSH &&
- ordered != QUEUE_ORDERED_TAG_FUA) {
+ ordered != QUEUE_ORDERED_DRAIN_FUA) {
printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
return -EINVAL;
}
@@ -155,21 +152,9 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
* For an empty barrier, there's no actual BAR request, which
* in turn makes POSTFLUSH unnecessary. Mask them off.
*/
- if (!blk_rq_sectors(rq)) {
+ if (!blk_rq_sectors(rq))
q->ordered &= ~(QUEUE_ORDERED_DO_BAR |
QUEUE_ORDERED_DO_POSTFLUSH);
- /*
- * Empty barrier on a write-through device w/ ordered
- * tag has no command to issue and without any command
- * to issue, ordering by tag can't be used. Drain
- * instead.
- */
- if ((q->ordered & QUEUE_ORDERED_BY_TAG) &&
- !(q->ordered & QUEUE_ORDERED_DO_PREFLUSH)) {
- q->ordered &= ~QUEUE_ORDERED_BY_TAG;
- q->ordered |= QUEUE_ORDERED_BY_DRAIN;
- }
- }

/* stash away the original request */
blk_dequeue_request(rq);
@@ -210,7 +195,7 @@ static inline bool start_ordered(struct request_queue *q, struct request **rqp)
} else
skip |= QUEUE_ORDSEQ_PREFLUSH;

- if ((q->ordered & QUEUE_ORDERED_BY_DRAIN) && queue_in_flight(q))
+ if (queue_in_flight(q))
rq = NULL;
else
skip |= QUEUE_ORDSEQ_DRAIN;
@@ -257,16 +242,10 @@ bool blk_do_ordered(struct request_queue *q, struct request **rqp)
rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
return true;

- if (q->ordered & QUEUE_ORDERED_BY_TAG) {
- /* Ordered by tag. Blocking the next barrier is enough. */
- if (is_barrier && rq != &q->bar_rq)
- *rqp = NULL;
- } else {
- /* Ordered by draining. Wait for turn. */
- WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
- if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
- *rqp = NULL;
- }
+ /* Ordered by draining. Wait for turn. */
+ WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
+ if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
+ *rqp = NULL;

return true;
}
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 1c7f637..47a4127 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -482,7 +482,7 @@ static struct brd_device *brd_alloc(int i)
if (!brd->brd_queue)
goto out_free_dev;
blk_queue_make_request(brd->brd_queue, brd_make_request);
- blk_queue_ordered(brd->brd_queue, QUEUE_ORDERED_TAG);
+ blk_queue_ordered(brd->brd_queue, QUEUE_ORDERED_DRAIN);
blk_queue_max_hw_sectors(brd->brd_queue, 1024);
blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 2aafafc..7965280 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -395,15 +395,6 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
* to implement write barrier support.
*/
blk_queue_ordered(q, QUEUE_ORDERED_DRAIN_FLUSH);
- } else if (virtio_has_feature(vdev, VIRTIO_BLK_F_BARRIER)) {
- /*
- * If the BARRIER feature is supported the host expects us
- * to order request by tags. This implies there is not
- * volatile write cache on the host, and that the host
- * never re-orders outstanding I/O. This feature is not
- * useful for real life scenarious and deprecated.
- */
- blk_queue_ordered(q, QUEUE_ORDERED_TAG);
} else {
/*
* If the FLUSH feature is not supported we must assume that
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 510ab86..25ffbf9 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -424,8 +424,7 @@ static int xlvbd_barrier(struct blkfront_info *info)
const char *barrier;

switch (info->feature_barrier) {
- case QUEUE_ORDERED_DRAIN: barrier = "enabled (drain)"; break;
- case QUEUE_ORDERED_TAG: barrier = "enabled (tag)"; break;
+ case QUEUE_ORDERED_DRAIN: barrier = "enabled"; break;
case QUEUE_ORDERED_NONE: barrier = "disabled"; break;
default: return -EINVAL;
}
@@ -1078,8 +1077,7 @@ static void blkfront_connect(struct blkfront_info *info)
* we're dealing with a very old backend which writes
* synchronously; draining will do what needs to get done.
*
- * If there are barriers, then we can do full queued writes
- * with tagged barriers.
+ * If there are barriers, then we use flush.
*
* If barriers are not supported, then there's no much we can
* do, so just set ordering to NONE.
@@ -1087,7 +1085,7 @@ static void blkfront_connect(struct blkfront_info *info)
if (err)
info->feature_barrier = QUEUE_ORDERED_DRAIN;
else if (barrier)
- info->feature_barrier = QUEUE_ORDERED_TAG;
+ info->feature_barrier = QUEUE_ORDERED_DRAIN_FLUSH;
else
info->feature_barrier = QUEUE_ORDERED_NONE;

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 8e2e893..05a15b0 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -2151,9 +2151,7 @@ static int sd_revalidate_disk(struct gendisk *disk)

/*
* We now have all cache related info, determine how we deal
- * with ordered requests. Note that as the current SCSI
- * dispatch function can alter request order, we cannot use
- * QUEUE_ORDERED_TAG_* even when ordered tag is supported.
+ * with ordered requests.
*/
if (sdkp->WCE)
ordered = sdkp->DPOFUA
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 89c855c..96ef5f1 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -469,12 +469,7 @@ enum {
* DRAIN : ordering by draining is enough
* DRAIN_FLUSH : ordering by draining w/ pre and post flushes
* DRAIN_FUA : ordering by draining w/ pre flush and FUA write
- * TAG : ordering by tag is enough
- * TAG_FLUSH : ordering by tag w/ pre and post flushes
- * TAG_FUA : ordering by tag w/ pre flush and FUA write
*/
- QUEUE_ORDERED_BY_DRAIN = 0x01,
- QUEUE_ORDERED_BY_TAG = 0x02,
QUEUE_ORDERED_DO_PREFLUSH = 0x10,
QUEUE_ORDERED_DO_BAR = 0x20,
QUEUE_ORDERED_DO_POSTFLUSH = 0x40,
@@ -482,8 +477,7 @@ enum {

QUEUE_ORDERED_NONE = 0x00,

- QUEUE_ORDERED_DRAIN = QUEUE_ORDERED_BY_DRAIN |
- QUEUE_ORDERED_DO_BAR,
+ QUEUE_ORDERED_DRAIN = QUEUE_ORDERED_DO_BAR,
QUEUE_ORDERED_DRAIN_FLUSH = QUEUE_ORDERED_DRAIN |
QUEUE_ORDERED_DO_PREFLUSH |
QUEUE_ORDERED_DO_POSTFLUSH,
@@ -491,15 +485,6 @@ enum {
QUEUE_ORDERED_DO_PREFLUSH |
QUEUE_ORDERED_DO_FUA,

- QUEUE_ORDERED_TAG = QUEUE_ORDERED_BY_TAG |
- QUEUE_ORDERED_DO_BAR,
- QUEUE_ORDERED_TAG_FLUSH = QUEUE_ORDERED_TAG |
- QUEUE_ORDERED_DO_PREFLUSH |
- QUEUE_ORDERED_DO_POSTFLUSH,
- QUEUE_ORDERED_TAG_FUA = QUEUE_ORDERED_TAG |
- QUEUE_ORDERED_DO_PREFLUSH |
- QUEUE_ORDERED_DO_FUA,
-
/*
* Ordered operation sequence
*/
--
1.7.1

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Prev: BUG: using smp_processor_id() in preemptible [00000000] code
Next: [PATCH 07/11] block: rename blk-barrier.c to blk-flush.c