netdev - Re: bug in qavg calculation in include/net/red.h (resending as plain-text email)

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Date:	Thu, 05 Jan 2012 21:13:20 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Yalagandula, Praveen" <praveen.yalagandula@...com>
Cc:	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: bug in qavg calculation in include/net/red.h (resending as
 plain-text email)

Le jeudi 05 janvier 2012 à 19:30 +0000, Yalagandula, Praveen a écrit :
> (Resending as plain text)
> 
> Dear Alexey,
> 
> The code (see below) for computing the queue average for RED
> implementation in Linux kernel has a bug. The return line should be
> "return p->qavg + ((backlog - p->qavg) >> p->Wlog);". 
> 
> qavg = qavg*(1-W) + backlog*W
> 
>      = qavg + (backlog-qavg)*W
> 
> The current buggy code applies right shift to only the previous qavg,
> where as it should be applied to (backlog - qavg). Hope you can get
> this bug corrected.

Code is correct.

Please read the comment, it really explains the thing.

Thanks


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