[PATCH 7/8] block: Add flag for telling the IO schedulers NOT to anticipate more IO
From: Jens Axboe
Date: Mon Apr 06 2009 - 08:50:53 EST
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@xxxxxxxxxx>
---
block/blk-core.c | 2 ++
block/cfq-iosched.c | 4 +++-
fs/direct-io.c | 2 +-
include/linux/bio.h | 19 +++++++++++--------
include/linux/blkdev.h | 3 +++
include/linux/fs.h | 9 +++++----
6 files changed, 25 insertions(+), 14 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index c4198f0..2557280 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 664ebfd..9e80934 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 b6d4390..da258e7 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 b05b1d4..b900d2c 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 67dae3b..e036609 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 ea05109..cae5720 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))
--
1.6.2.1.423.g442d
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