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cfq-iosched: rethink seeky detection for SSDs 

CFQ currently applies the same logic of detecting seeky queues and
grouping them together for rotational disks as well as SSDs.
For SSDs, the time to complete a request doesn't depend on the
request location, but only on the size.
This patch therefore changes the criterion to group queues by
request size in case of SSDs, in order to achieve better fairness.

Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Corrado Zoccolo 2010-02-27 19:45:40 +01:00 committed by Jens Axboe
parent 3dde36ddea
commit 41647e7a91
1 changed files with 6 additions and 1 deletions
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7
block/cfq-iosched.c
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@ -47,6 +47,7 @@ static const int cfq_hist_divisor = 4;
#define CFQ_SERVICE_SHIFT 12
#define CFQQ_SEEK_THR (sector_t)(8 * 100)
#define CFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
#define CFQQ_SEEKY(cfqq) (hweight32(cfqq->seek_history) > 32/8)
#define RQ_CIC(rq) \
@ -2965,6 +2966,7 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
struct request *rq)
{
sector_t sdist = 0;
sector_t n_sec = blk_rq_sectors(rq);
if (cfqq->last_request_pos) {
if (cfqq->last_request_pos < blk_rq_pos(rq))
sdist = blk_rq_pos(rq) - cfqq->last_request_pos;
@ -2973,7 +2975,10 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
}
cfqq->seek_history <<= 1;
cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);
if (blk_queue_nonrot(cfqd->queue))
cfqq->seek_history |= (n_sec < CFQQ_SECT_THR_NONROT);
else
cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);
}
/*