[PATCH]cfq-iosched: split seeky coop queues after one slice

[Shaohua Li]

On Fri, Dec 25, 2009 at 06:16:27PM +0800, Corrado Zoccolo wrote:
> Hi Shaohua,
> On Thu, Dec 24, 2009 at 1:55 AM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote:
> > df5fe3e8e13883f58dc97489076bbcc150789a21
> > b3b6d0408c953524f979468562e7e210d8634150
> > The coop merge is too aggressive. For example, if two tasks are reading two
> > files where the two files have some adjecent blocks, cfq will immediately
> > merge them. cfq_rq_close() also has trouble, sometimes the seek_mean is very
> > big. I did a test to make cfq_rq_close() always checks the distence according
> > to CIC_SEEK_THR, but still saw a lot of wrong merge. (BTW, why we take a long
> > distence far away request as close. Taking them close doesn't improve any thoughtput
> > to me. Maybe we should always use CIC_SEEK_THR as close criteria).
> Yes, when deciding if two queues are going to be merged, we should use
> the constant CIC_SEEK_THR.
> > So sounds we need make split more aggressive. But the split is too lazay,
> > which requires to wait 1s. Time based check isn't reliable as queue might not
> > run at given time, so uses a small time isn't ok.
> 1s is too much, but I wouldn't abandon a time based approach. To fix
> the problem of queue not being run, you can consider a slice. If at
> the end of the slice, the queue is seeky, you split it.

Currently we split seeky coop queues after 1s, which is too big. Below patch
marks seeky coop queue split_coop flag after one slice. After that, if new
requests come in, the queues will be splitted. Patch is suggested by Corrado.

Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index e2f8046..d4d5cca 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -52,6 +52,9 @@ static const int cfq_hist_divisor = 4;
 #define CFQ_HW_QUEUE_MIN	(5)
 #define CFQ_SERVICE_SHIFT       12
 
+#define CFQQ_SEEK_THR		8 * 1024
+#define CFQQ_SEEKY(cfqq)	((cfqq)->seek_mean > CFQQ_SEEK_THR)
+
 #define RQ_CIC(rq)		\
 	((struct cfq_io_context *) (rq)->elevator_private)
 #define RQ_CFQQ(rq)		(struct cfq_queue *) ((rq)->elevator_private2)
@@ -137,7 +140,6 @@ struct cfq_queue {
 	u64 seek_total;
 	sector_t seek_mean;
 	sector_t last_request_pos;
-	unsigned long seeky_start;
 
 	pid_t pid;
 
@@ -317,6 +319,7 @@ enum cfqq_state_flags {
 	CFQ_CFQQ_FLAG_slice_new,	/* no requests dispatched in slice */
 	CFQ_CFQQ_FLAG_sync,		/* synchronous queue */
 	CFQ_CFQQ_FLAG_coop,		/* cfqq is shared */
+	CFQ_CFQQ_FLAG_split_coop,	/* shared cfqq will be splitted */
 	CFQ_CFQQ_FLAG_deep,		/* sync cfqq experienced large depth */
 	CFQ_CFQQ_FLAG_wait_busy,	/* Waiting for next request */
 };
@@ -345,6 +348,7 @@ CFQ_CFQQ_FNS(prio_changed);
 CFQ_CFQQ_FNS(slice_new);
 CFQ_CFQQ_FNS(sync);
 CFQ_CFQQ_FNS(coop);
+CFQ_CFQQ_FNS(split_coop);
 CFQ_CFQQ_FNS(deep);
 CFQ_CFQQ_FNS(wait_busy);
 #undef CFQ_CFQQ_FNS
@@ -1574,6 +1578,15 @@ __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 	cfq_clear_cfqq_wait_busy(cfqq);
 
 	/*
+	 * If this cfqq is shared between multiple processes, check to
+	 * make sure that those processes are still issuing I/Os within
+	 * the mean seek distance.  If not, it may be time to break the
+	 * queues apart again.
+	 */
+	if (cfq_cfqq_coop(cfqq) && CFQQ_SEEKY(cfqq))
+		cfq_mark_cfqq_split_coop(cfqq);
+
+	/*
 	 * store what was left of this slice, if the queue idled/timed out
 	 */
 	if (timed_out && !cfq_cfqq_slice_new(cfqq)) {
@@ -1671,9 +1684,6 @@ static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
 		return cfqd->last_position - blk_rq_pos(rq);
 }
 
-#define CFQQ_SEEK_THR		8 * 1024
-#define CFQQ_SEEKY(cfqq)	((cfqq)->seek_mean > CFQQ_SEEK_THR)
-
 static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 			       struct request *rq)
 {
@@ -3027,19 +3037,6 @@ cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 	total = cfqq->seek_total + (cfqq->seek_samples/2);
 	do_div(total, cfqq->seek_samples);
 	cfqq->seek_mean = (sector_t)total;
-
-	/*
-	 * If this cfqq is shared between multiple processes, check to
-	 * make sure that those processes are still issuing I/Os within
-	 * the mean seek distance.  If not, it may be time to break the
-	 * queues apart again.
-	 */
-	if (cfq_cfqq_coop(cfqq)) {
-		if (CFQQ_SEEKY(cfqq) && !cfqq->seeky_start)
-			cfqq->seeky_start = jiffies;
-		else if (!CFQQ_SEEKY(cfqq))
-			cfqq->seeky_start = 0;
-	}
 }
 
 /*
@@ -3474,14 +3471,6 @@ cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_context *cic,
 	return cic_to_cfqq(cic, 1);
 }
 
-static int should_split_cfqq(struct cfq_queue *cfqq)
-{
-	if (cfqq->seeky_start &&
-	    time_after(jiffies, cfqq->seeky_start + CFQQ_COOP_TOUT))
-		return 1;
-	return 0;
-}
-
 /*
  * Returns NULL if a new cfqq should be allocated, or the old cfqq if this
  * was the last process referring to said cfqq.
@@ -3490,9 +3479,9 @@ static struct cfq_queue *
 split_cfqq(struct cfq_io_context *cic, struct cfq_queue *cfqq)
 {
 	if (cfqq_process_refs(cfqq) == 1) {
-		cfqq->seeky_start = 0;
 		cfqq->pid = current->pid;
 		cfq_clear_cfqq_coop(cfqq);
+		cfq_clear_cfqq_split_coop(cfqq);
 		return cfqq;
 	}
 
@@ -3531,7 +3520,7 @@ new_queue:
 		/*
 		 * If the queue was seeky for too long, break it apart.
 		 */
-		if (cfq_cfqq_coop(cfqq) && should_split_cfqq(cfqq)) {
+		if (cfq_cfqq_coop(cfqq) && cfq_cfqq_split_coop(cfqq)) {
 			cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");
 			cfqq = split_cfqq(cic, cfqq);
 			if (!cfqq)
--
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