netdev - Re: problem with noop and pfifo

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Message-ID: <1326978933.2249.6.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Thu, 19 Jan 2012 14:15:33 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hemant-vilas RAMDASI <hemant.ramdasi@...ricsson.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>
Subject: Re: problem with noop and pfifo_fast Qdisc switching

Le jeudi 19 janvier 2012 à 13:47 +0100, Hemant-vilas RAMDASI a écrit :
> Hi,
> 
> I have a situation where one of important message (phonet pipe message) gets dropped because of 'noop' Qdisc.
> This situation mostly happens when coming out of sleep and there is a message to send.
> What I have observed is this.
> In normal case the qdisc used id pfifo_fast. When CPU goes to sleep, it changes the qdisc to noop.
> When CPU wakes up (because of a message from lower layers), phonet tries to send a control packet to driver and finds qdisc is still 'noop'. 
> Because the concerned message is a control message, this packet drop is creating deadlock situation.
> 
> How the switch between pfifo_fast and noop is handled? Is this something solved in 3.0?
> We are running a older version of kernel (2.6.35 based).

If message is important, you should check return code from xmit
(NET_XMIT_CN is returned by noop_enqueue), and maybe resend it later.

Not sure by what you mean by 'cpu goes to sleep' or 'cpu wakes up' ?

Is it the machine going to suspend mode ?


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