block: Add flag for telling the IO schedulers NOT to anticipate more IO

By default, CFQ will anticipate more IO from a given io context if the
previously completed IO was sync. This used to be fine, since the only
sync IO was reads and O_DIRECT writes. But with more "normal" sync writes
being used now, we don't want to anticipate for those.

Add a bio/request flag that informs the IO scheduler that this is a sync
request that we should not idle for. Introduce WRITE_ODIRECT specifically
for O_DIRECT writes, and make sure that the other sync writes set this
flag.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

6 files changed, 25 insertions, 14 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index c4198f083e5b..25572802dac2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1128,6 +1128,8 @@ void init_request_from_bio(struct request *req, struct bio *bio)
                 req->cmd_flags |= REQ_UNPLUG;
         if (bio_rw_meta(bio))
                 req->cmd_flags |= REQ_RW_META;
+        if (bio_noidle(bio))
+                req->cmd_flags |= REQ_NOIDLE;
 
         req->errors = 0;
         req->hard_sector = req->sector = bio->bi_sector;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 664ebfd092ec..9e809345f71a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1992,8 +1992,10 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
                 }
                 if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
                         cfq_slice_expired(cfqd, 1);
-                else if (sync && RB_EMPTY_ROOT(&cfqq->sort_list))
+                else if (sync && !rq_noidle(rq) &&
+                         RB_EMPTY_ROOT(&cfqq->sort_list)) {
                         cfq_arm_slice_timer(cfqd);
+                }
         }
 
         if (!cfqd->rq_in_driver)
diff --git a/fs/direct-io.c b/fs/direct-io.c
index b6d43908ff7a..da258e7249cc 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1126,7 +1126,7 @@ __blockdev_direct_IO(int rw, struct kiocb *iocb, struct inode *inode,
         int acquire_i_mutex = 0;
 
         if (rw & WRITE)
-                rw = WRITE_SYNC;
+                rw = WRITE_ODIRECT;
 
         if (bdev)
                 bdev_blkbits = blksize_bits(bdev_hardsect_size(bdev));
diff --git a/include/linux/bio.h b/include/linux/bio.h
index b05b1d4d17d2..b900d2c67d29 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -145,20 +145,21 @@ struct bio {
  * bit 2 -- barrier
  *      Insert a serialization point in the IO queue, forcing previously
  *      submitted IO to be completed before this one is issued.
- * bit 3 -- synchronous I/O hint: the block layer will unplug immediately
- *      Note that this does NOT indicate that the IO itself is sync, just
- *      that the block layer will not postpone issue of this IO by plugging.
- * bit 4 -- metadata request
+ * bit 3 -- synchronous I/O hint.
+ * bit 4 -- Unplug the device immediately after submitting this bio.
+ * bit 5 -- metadata request
  *      Used for tracing to differentiate metadata and data IO. May also
  *      get some preferential treatment in the IO scheduler
- * bit 5 -- discard sectors
+ * bit 6 -- discard sectors
  *      Informs the lower level device that this range of sectors is no longer
  *      used by the file system and may thus be freed by the device. Used
  *      for flash based storage.
- * bit 6 -- fail fast device errors
- * bit 7 -- fail fast transport errors
- * bit 8 -- fail fast driver errors
+ * bit 7 -- fail fast device errors
+ * bit 8 -- fail fast transport errors
+ * bit 9 -- fail fast driver errors
  *      Don't want driver retries for any fast fail whatever the reason.
+ * bit 10 -- Tell the IO scheduler not to wait for more requests after this
+        one has been submitted, even if it is a SYNC request.
  */
 #define BIO_RW          0       /* Must match RW in req flags (blkdev.h) */
 #define BIO_RW_AHEAD    1       /* Must match FAILFAST in req flags */
@@ -170,6 +171,7 @@ struct bio {
 #define BIO_RW_FAILFAST_DEV             7
 #define BIO_RW_FAILFAST_TRANSPORT       8
 #define BIO_RW_FAILFAST_DRIVER          9
+#define BIO_RW_NOIDLE   10
 
 #define bio_rw_flagged(bio, flag)       ((bio)->bi_rw & (1 << (flag)))
 
@@ -188,6 +190,7 @@ struct bio {
 #define bio_rw_ahead(bio)       bio_rw_flagged(bio, BIO_RW_AHEAD)
 #define bio_rw_meta(bio)        bio_rw_flagged(bio, BIO_RW_META)
 #define bio_discard(bio)        bio_rw_flagged(bio, BIO_RW_DISCARD)
+#define bio_noidle(bio)         bio_rw_flagged(bio, BIO_RW_NOIDLE)
 
 /*
  * upper 16 bits of bi_rw define the io priority of this bio
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 67dae3bd881c..e03660964e02 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -118,6 +118,7 @@ enum rq_flag_bits {
         __REQ_COPY_USER,        /* contains copies of user pages */
         __REQ_INTEGRITY,        /* integrity metadata has been remapped */
         __REQ_UNPLUG,           /* unplug queue on submission */
+        __REQ_NOIDLE,           /* Don't anticipate more IO after this one */
         __REQ_NR_BITS,          /* stops here */
 };
 
@@ -145,6 +146,7 @@ enum rq_flag_bits {
 #define REQ_COPY_USER   (1 << __REQ_COPY_USER)
 #define REQ_INTEGRITY   (1 << __REQ_INTEGRITY)
 #define REQ_UNPLUG      (1 << __REQ_UNPLUG)
+#define REQ_NOIDLE      (1 << __REQ_NOIDLE)
 
 #define BLK_MAX_CDB     16
 
@@ -633,6 +635,7 @@ static inline bool rq_is_sync(struct request *rq)
 }
 
 #define rq_is_meta(rq)          ((rq)->cmd_flags & REQ_RW_META)
+#define rq_noidle(rq)           ((rq)->cmd_flags & REQ_NOIDLE)
 
 static inline int blk_queue_full(struct request_queue *q, int sync)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ea0510978f76..cae5720f431c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -95,11 +95,12 @@ struct inodes_stat_t {
 #define SWRITE 3        /* for ll_rw_block() - wait for buffer lock */
 #define READ_SYNC       (READ | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
 #define READ_META       (READ | (1 << BIO_RW_META))
-#define WRITE_SYNC      (WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
-#define WRITE_SYNC_PLUG (WRITE | (1 << BIO_RW_SYNCIO))
-#define SWRITE_SYNC     (SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
+#define WRITE_SYNC_PLUG (WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
+#define WRITE_SYNC      (WRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
+#define WRITE_ODIRECT   (WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_UNPLUG))
 #define SWRITE_SYNC_PLUG        \
-        (SWRITE | (1 << BIO_RW_SYNCIO))
+                        (SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
+#define SWRITE_SYNC     (SWRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
 #define WRITE_BARRIER   (WRITE | (1 << BIO_RW_BARRIER))
 #define DISCARD_NOBARRIER (1 << BIO_RW_DISCARD)
 #define DISCARD_BARRIER ((1 << BIO_RW_DISCARD) | (1 << BIO_RW_BARRIER))