netdev - Re: [PATCH] tcp_cubic: limit delayed_ack ratio to prevent divide error

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Message-ID: <20110506095359.57c4fb38@nehalam>
Date:	Fri, 6 May 2011 09:53:59 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	TB <lkml@...hboom.com>
Cc:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	David Miller <davem@...emloft.net>,
	Sangtae Ha <sangtae.ha@...il.com>,
	Injong Rhee <injongrhee@...il.com>,
	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>,
	"rdunlap@...otime.net" <rdunlap@...otime.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tcp_cubic: limit delayed_ack ratio to prevent divide
 error

On Fri, 06 May 2011 12:15:46 -0400
TB <lkml@...hboom.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On 11-05-04 04:53 PM, Brandeburg, Jesse wrote:
> > 
> > 
> > On Wed, 4 May 2011, Stephen Hemminger wrote:
> > 
> >> TCP Cubic keeps a metric that estimates the amount of delayed
> >> acknowledgements to use in adjusting the window. If an abnormally
> >> large number of packets are acknowledged at once, then the update
> >> could wrap and reach zero. This kind of ACK could only
> >> happen when there was a large window and huge number of
> >> ACK's were lost.
> >>
> >> This patch limits the value of delayed ack ratio. The choice of 32
> >> is just a conservative value since normally it should be range of 
> >> 1 to 4 packets.
> >>
> >> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > patch seems fine, but please credit the reporter (lkml@...hboom.com) with 
> > reporting the issue with logs, maybe even with Reported-by: and some kind 
> > of reference to the panic message or the email thread in the text or 
> > header?
> 
> We're currently testing the patch on 6 production servers

Thank you, is there some regularity to the failures previously?
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