netdev - [PATCH iproute2] red: give a hint about burst value

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Message-ID: <1322737471.2335.25.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Thu, 01 Dec 2011 12:04:31 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Stephen Hemminger <shemminger@...tta.com>
Subject: [PATCH iproute2] red: give a hint about burst value

Le mercredi 30 novembre 2011 à 23:44 +0100, Eric Dumazet a écrit :
> Le mercredi 30 novembre 2011 à 23:35 +0100, Dave Taht a écrit :
> 
> > One of my other problems is when I try to size red (or choke) appropriately
> > (or so I think) for GigE bandwidths and queue depths, it would fail
> > to calculate the ewma value.
> 
> Do you have one example of such failure ?
> 

Oh I understand your burst value is really too small.

Stephen, can we add this helper to iproute2 ?

[PATCH iproute2] red: try to give hint about burst value

Reported-by: Dave Taht <dave.taht@...il.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
diff --git a/tc/tc_red.c b/tc/tc_red.c
index 66658ca..a65435e 100644
--- a/tc/tc_red.c
+++ b/tc/tc_red.c
@@ -56,8 +56,11 @@ int tc_red_eval_ewma(unsigned qmin, unsigned burst, unsigned avpkt)
 	double W = 0.5;
 	double a = (double)burst + 1 - (double)qmin/avpkt;
 
-	if (a < 1.0)
+	if (a < 1.0) {
+		fprintf(stderr, "tc_red_eval_ewma() burst %u is too small ?"
+				" Try burst %u\n", burst, 1 + qmin/avpkt);
 		return -1;
+	}
 	for (wlog=1; wlog<32; wlog++, W /= 2) {
 		if (a <= (1 - pow(1-W, burst))/W)
 			return wlog;


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