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Subject[PATCH] sch_red: fix weighted average calculation
Date
This patch fixes an apparent bug in the running weighted average calculation
used in the RED algorithm.

Going by the described formula:
qavg = qavg*(1-W) + backlog*W
=> qavg = qavg + (backlog - qavg) * W

... with W converted to a pre-calculated shift, this then becomes:
qavg = qavg + (backlog - qavg) >> logW

... giving the modified expression introduced by this patch.

Signed-off-by: John Dowdal <jdowdal@ti.com>
---
include/net/red.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/red.h b/include/net/red.h
index ef46058..05960a4 100644
--- a/include/net/red.h
+++ b/include/net/red.h
@@ -287,7 +287,7 @@ static inline unsigned long red_calc_qavg_no_idle_time(const struct red_parms *p
*
* --ANK (980924)
*/
- return v->qavg + (backlog - (v->qavg >> p->Wlog));
+ return v->qavg + (backlog - v->qavg) >> p->Wlog;
}

static inline unsigned long red_calc_qavg(const struct red_parms *p,
--
1.7.9.5


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