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From: Corrado Zoccolo on 7 Jul 2010 12:00
Patch: 8e55063 cfq-iosched: fix corner cases in idling logic
introduced the possibility of iding even on no-idle requests
in the no_idle tree, if any previous request in the current slice
could idle. The implementation had a problem, though:
- if a queue sent several possibly idling requests and a noidle
request as last one in the same time slice, the tree was still
marked as idle.
This patch fixes this misbehaviour, by using a 31-bucket hash to
keep idling/non-idling status for queues in the noidle tree.

Signed-off-by: Corrado Zoccolo <czoccolo(a)gmail.com>
---
block/cfq-iosched.c | 15 ++++++++++-----
1 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index eb4086f..596b747 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -216,7 +216,7 @@ struct cfq_data {
enum wl_type_t serving_type;
unsigned long workload_expires;
struct cfq_group *serving_group;
- bool noidle_tree_requires_idle;
+ u32 noidle_tree_requires_idle;

/*
* Each priority tree is sorted by next_request position. These
@@ -2126,7 +2126,7 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
slice = max_t(unsigned, slice, CFQ_MIN_TT);
cfq_log(cfqd, "workload slice:%d", slice);
cfqd->workload_expires = jiffies + slice;
- cfqd->noidle_tree_requires_idle = false;
+ cfqd->noidle_tree_requires_idle = 0U;
}

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
@@ -3421,12 +3421,17 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
cfq_slice_expired(cfqd, 1);
else if (sync && cfqq_empty &&
!cfq_close_cooperator(cfqd, cfqq)) {
- cfqd->noidle_tree_requires_idle |=
- !(rq->cmd_flags & REQ_NOIDLE);
+ u32 bitmask = 1U << (((int)cfqq) % 31);
+ if (rq->cmd_flags & REQ_NOIDLE)
+ cfqd->noidle_tree_requires_idle &= ~bitmask;
+ else
+ cfqd->noidle_tree_requires_idle |= bitmask;
+
/*
* Idling is enabled for SYNC_WORKLOAD.
* SYNC_NOIDLE_WORKLOAD idles at the end of the tree
- * only if we processed at least one !REQ_NOIDLE request
+ * only if at least one queue sent !RQ_NOIDLE requests
+ * not followed by at least one RQ_NOIDLE request.
*/
if (cfqd->serving_type == SYNC_WORKLOAD
|| cfqd->noidle_tree_requires_idle
--
1.6.4.4

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