Re: [PATCH] sch_red: fix weighted average calculation
From: Eric Dumazet <hidden>
Date: 2012-09-13 13:54:00
Also in:
lkml
On Thu, 2012-09-13 at 09:43 -0400, Cyril Chemparathy wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- 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,
This is going to be a FPP (Frequently Posted Patch) Current formulae is fine. Thats because backlog, at start of red_calc_qavg_no_idle_time() is not yet scaled by p->Wlog. v->avg is scaled, but not backlog. Have you tested RED after your patch ?