linux-kernel - [PATCH 1/2] cfq-iosched: fix tree-wide handling of rq

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Date:	Wed,  7 Jul 2010 17:55:44 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	Corrado Zoccolo <czoccolo@...il.com>
Subject: [PATCH 1/2] cfq-iosched: fix tree-wide handling of rq_noidle

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@...il.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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