diff options
| author | Corrado Zoccolo <czoccolo@gmail.com> | 2009-11-08 17:16:46 +0100 |
|---|---|---|
| committer | Jens Axboe <jens.axboe@oracle.com> | 2009-11-08 17:16:46 +0100 |
| commit | cf7c25cf91f632a3528669fc0876e1fc8355ff9b (patch) | |
| tree | 7967e65544dd49cb7333363ec928722a9e4a1562 /block | |
| parent | 622d32d3ec40d5075523656ef0ea836f6a595ae3 (diff) | |
cfq-iosched: fix next_rq computation
Cfq has a bug in computation of next_rq, that affects transition
between multiple sequential request streams in a single queue
(e.g.: two sequential buffered writers of the same priority),
causing the alternation between the two streams for a transient period.
8,0 1 18737 0.260400660 5312 D W 141653311 + 256
8,0 1 20839 0.273239461 5400 D W 141653567 + 256
8,0 1 20841 0.276343885 5394 D W 142803919 + 256
8,0 1 20843 0.279490878 5394 D W 141668927 + 256
8,0 1 20845 0.292459993 5400 D W 142804175 + 256
8,0 1 20847 0.295537247 5400 D W 141668671 + 256
8,0 1 20849 0.298656337 5400 D W 142804431 + 256
8,0 1 20851 0.311481148 5394 D W 141668415 + 256
8,0 1 20853 0.314421305 5394 D W 142804687 + 256
8,0 1 20855 0.318960112 5400 D W 142804943 + 256
The fix makes sure that the next_rq is computed from the last
dispatched request, and not affected by merging.
8,0 1 37776 4.305161306 0 D W 141738087 + 256
8,0 1 37778 4.308298091 0 D W 141738343 + 256
8,0 1 37780 4.312885190 0 D W 141738599 + 256
8,0 1 37782 4.315933291 0 D W 141738855 + 256
8,0 1 37784 4.319064459 0 D W 141739111 + 256
8,0 1 37786 4.331918431 5672 D W 142803007 + 256
8,0 1 37788 4.334930332 5672 D W 142803263 + 256
8,0 1 37790 4.337902723 5672 D W 142803519 + 256
8,0 1 37792 4.342359774 5672 D W 142803775 + 256
8,0 1 37794 4.345318286 0 D W 142804031 + 256
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Diffstat (limited to 'block')
| -rw-r--r-- | block/cfq-iosched.c | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 4ab240c875d..829d87d3e00 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -454,9 +454,9 @@ static inline bool cfq_slice_used(struct cfq_queue *cfqq) * behind the head is penalized and only allowed to a certain extent. */ static struct request * -cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2) +cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last) { - sector_t last, s1, s2, d1 = 0, d2 = 0; + sector_t s1, s2, d1 = 0, d2 = 0; unsigned long back_max; #define CFQ_RQ1_WRAP 0x01 /* request 1 wraps */ #define CFQ_RQ2_WRAP 0x02 /* request 2 wraps */ @@ -479,8 +479,6 @@ cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2) s1 = blk_rq_pos(rq1); s2 = blk_rq_pos(rq2); - last = cfqd->last_position; - /* * by definition, 1KiB is 2 sectors */ @@ -595,7 +593,7 @@ cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq, next = rb_entry_rq(rbnext); } - return cfq_choose_req(cfqd, next, prev); + return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last)); } static unsigned long cfq_slice_offset(struct cfq_data *cfqd, @@ -843,7 +841,7 @@ static void cfq_add_rq_rb(struct request *rq) * check if this request is a better next-serve candidate */ prev = cfqq->next_rq; - cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq); + cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position); /* * adjust priority tree position, if ->next_rq changes @@ -950,6 +948,7 @@ static void cfq_merged_requests(struct request_queue *q, struct request *rq, struct request *next) { + struct cfq_queue *cfqq = RQ_CFQQ(rq); /* * reposition in fifo if next is older than rq */ @@ -959,6 +958,8 @@ cfq_merged_requests(struct request_queue *q, struct request *rq, rq_set_fifo_time(rq, rq_fifo_time(next)); } + if (cfqq->next_rq == next) + cfqq->next_rq = rq; cfq_remove_request(next); } |