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

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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>
This commit is contained in:
Jens Axboe 2009-04-06 14:48:07 +02:00 • committed by Linus Torvalds
parent 644b2d99b7
commit aeb6fafb8f
6 changed files with 25 additions and 14 deletions
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19
include/linux/bio.h
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@ -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