Commit 9c2c38a1 authored by Jens Axboe's avatar Jens Axboe Committed by Linus Torvalds
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[PATCH] cfq-iosched.c: minor fixes

One critical fix and two minor fixes for 2.6.13-rc7:

- Max depth must currently be 2 to allow barriers to function on SCSI
- Prefer sync request over async in choosing the next request
- Never allow async request to preempt or disturb the "anticipation" for
  a single cfq process context. This is as-designed, the code right now
  is buggy in that area.
Signed-off-by: default avatarJens Axboe <>
Signed-off-by: default avatarLinus Torvalds <>
parent 41290c14
......@@ -47,7 +47,7 @@ static int cfq_slice_idle = HZ / 100;
* disable queueing at the driver/hardware level
static int cfq_max_depth = 1;
static int cfq_max_depth = 2;
* for the hash of cfqq inside the cfqd
......@@ -385,9 +385,15 @@ cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2)
return crq2;
if (crq2 == NULL)
return crq1;
if (cfq_crq_requeued(crq1))
if (cfq_crq_requeued(crq1) && !cfq_crq_requeued(crq2))
return crq1;
else if (cfq_crq_requeued(crq2) && !cfq_crq_requeued(crq1))
return crq2;
if (cfq_crq_is_sync(crq1) && !cfq_crq_is_sync(crq2))
return crq1;
if (cfq_crq_requeued(crq2))
else if (cfq_crq_is_sync(crq2) && !cfq_crq_is_sync(crq1))
return crq2;
s1 = crq1->request->sector;
......@@ -1769,18 +1775,23 @@ static void
cfq_crq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
struct cfq_rq *crq)
const int sync = cfq_crq_is_sync(crq);
struct cfq_io_context *cic;
cfqq->next_crq = cfq_choose_req(cfqd, cfqq->next_crq, crq);
if (sync) {
struct cfq_io_context *cic = crq->io_context;
* we never wait for an async request and we don't allow preemption
* of an async request. so just return early
if (!cfq_crq_is_sync(crq))
cic = crq->io_context;
cfq_update_io_thinktime(cfqd, cic);
cfq_update_idle_window(cfqd, cfqq, cic);
cic->last_queue = jiffies;
if (cfqq == cfqd->active_queue) {
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