aoe: improve retransmission heuristics

Add a dynamic minimum timer for better retransmission behavior.
Signed-off-by: "Ed L. Cashin" <ecashin@coraid.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/block/aoe/aoe.h

@@ -125,8 +125,10 @@ struct aoedev {
 	ulong sysminor;
 	ulong aoemajor;
 	ulong aoeminor;
-	ulong nopen;		/* (bd_openers isn't available without sleeping) */
-	ulong rttavg;		/* round trip average of requests/responses */
+	u16 nopen;		/* (bd_openers isn't available without sleeping) */
+	u16 lasttag;		/* last tag sent */
+	u16 rttavg;		/* round trip average of requests/responses */
+	u16 mintimer;
 	u16 fw_ver;		/* version of blade's firmware */
 	u16 maxbcnt;
 	struct work_struct work;/* disk create work struct */
@@ -142,7 +144,6 @@ struct aoedev {
 	mempool_t *bufpool;	/* for deadlock-free Buf allocation */
 	struct list_head bufq;	/* queue of bios to work on */
 	struct buf *inprocess;	/* the one we're currently working on */
-	ulong lasttag;		/* last tag sent */
 	ushort lostjumbo;
 	ushort nframes;		/* number of frames below */
 	struct frame *frames;

drivers/block/aoe/aoecmd.c

@@ -461,10 +461,17 @@ calc_rttavg(struct aoedev *d, int rtt)
 	register long n;
 
 	n = rtt;
+	if (n < 0) {
+		n = -rtt;
 		if (n < MINTIMER)
 			n = MINTIMER;
 		else if (n > MAXTIMER)
 			n = MAXTIMER;
+		d->mintimer += (n - d->mintimer) >> 1;
+	} else if (n < d->mintimer)
+		n = d->mintimer;
+	else if (n > MAXTIMER)
+		n = MAXTIMER;
 
 	/* g == .25; cf. Congestion Avoidance and Control, Jacobson & Karels; 1988 */
 	n -= d->rttavg;
@@ -498,8 +505,10 @@ aoecmd_ata_rsp(struct sk_buff *skb)
 
 	spin_lock_irqsave(&d->lock, flags);
 
-	f = getframe(d, be32_to_cpu(hin->tag));
+	n = be32_to_cpu(hin->tag);
+	f = getframe(d, n);
 	if (f == NULL) {
+		calc_rttavg(d, -tsince(n));
 		spin_unlock_irqrestore(&d->lock, flags);
 		snprintf(ebuf, sizeof ebuf,
 			"%15s e%d.%d    tag=%08x@%08lx\n",
@@ -724,6 +733,7 @@ aoecmd_cfg_rsp(struct sk_buff *skb)
 		return;
 	}
 	d->flags |= DEVFL_PAUSE;	/* force pause */
+	d->mintimer = MINTIMER;
 	d->fw_ver = be16_to_cpu(ch->fwver);
 
 	/* check for already outstanding ataid */