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authorEric Dumazet <eric.dumazet@gmail.com>2011-12-08 06:06:03 +0000
committerDavid S. Miller <davem@davemloft.net>2011-12-08 19:52:43 -0500
commit8af2a218de38f51ea4b4fa48cac1273319ae260c (patch)
tree07a4557322b79878096172355fb02ab2bae3f432 /lib
parent57459185a19b0246866479522b77cbb9732201d1 (diff)
sch_red: Adaptative RED AQM
Adaptative RED AQM for linux, based on paper from Sally FLoyd, Ramakrishna Gummadi, and Scott Shenker, August 2001 : http://icir.org/floyd/papers/adaptiveRed.pdf Goal of Adaptative RED is to make max_p a dynamic value between 1% and 50% to reach the target average queue : (max_th - min_th) / 2 Every 500 ms: if (avg > target and max_p <= 0.5) increase max_p : max_p += alpha; else if (avg < target and max_p >= 0.01) decrease max_p : max_p *= beta; target :[min_th + 0.4*(min_th - max_th), min_th + 0.6*(min_th - max_th)]. alpha : min(0.01, max_p / 4) beta : 0.9 max_P is a Q0.32 fixed point number (unsigned, with 32 bits mantissa) Changes against our RED implementation are : max_p is no longer a negative power of two (1/(2^Plog)), but a Q0.32 fixed point number, to allow full range described in Adatative paper. To deliver a random number, we now use a reciprocal divide (thats really a multiply), but this operation is done once per marked/droped packet when in RED_BETWEEN_TRESH window, so added cost (compared to previous AND operation) is near zero. dump operation gives current max_p value in a new TCA_RED_MAX_P attribute. Example on a 10Mbit link : tc qdisc add dev $DEV parent 1:1 handle 10: est 1sec 8sec red \ limit 400000 min 30000 max 90000 avpkt 1000 \ burst 55 ecn adaptative bandwidth 10Mbit # tc -s -d qdisc show dev eth3 ... qdisc red 10: parent 1:1 limit 400000b min 30000b max 90000b ecn adaptative ewma 5 max_p=0.113335 Scell_log 15 Sent 50414282 bytes 34504 pkt (dropped 35, overlimits 1392 requeues 0) rate 9749Kbit 831pps backlog 72056b 16p requeues 0 marked 1357 early 35 pdrop 0 other 0 Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'lib')
-rw-r--r--lib/reciprocal_div.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/lib/reciprocal_div.c b/lib/reciprocal_div.c
index 6a3bd48fa2a..75510e94f7d 100644
--- a/lib/reciprocal_div.c
+++ b/lib/reciprocal_div.c
@@ -1,5 +1,6 @@
#include <asm/div64.h>
#include <linux/reciprocal_div.h>
+#include <linux/export.h>
u32 reciprocal_value(u32 k)
{
@@ -7,3 +8,4 @@ u32 reciprocal_value(u32 k)
do_div(val, k);
return (u32)val;
}
+EXPORT_SYMBOL(reciprocal_value);