netdev - RE: [PATCH] igb: Record hardware RX overruns in net

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Message-Id: <1241597562.5172.25.camel@localhost.localdomain>
Date:	Wed, 06 May 2009 10:12:42 +0200
From:	Jesper Dangaard Brouer <hawk@...x.dk>
To:	"Ronciak, John" <john.ronciak@...el.com>
Cc:	Jesper Dangaard Brouer <hawk@...u.dk>,
	David Miller <davem@...emloft.net>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	netdev <netdev@...r.kernel.org>,
	"e1000-devel@...ts.sourceforge.net" 
	<e1000-devel@...ts.sourceforge.net>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Allan, Bruce W" <bruce.w.allan@...el.com>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>
Subject: RE: [PATCH] igb: Record hardware RX overruns in net_stats

On Tue, 2009-05-05 at 15:38 -0700, Ronciak, John wrote:
> >Its really useful for diagnosing problems, and I'm betting 
> >that this is a real-life situation which people is going to experience. We 
> >might as well help our self to more easily identify this issue when people 
> >report drop problems.
>
> The problem is that the RNBC aren't dropped packets as the numbers you
> have show.  

Just to make it clear, I am experiencing dropped packets.  The reason I
positivly know this, is that I'm writing a MPEG2-TS drop detection
netfilter module.  Which were the only reason I discovered the packet
drops and the "hidden" RNBC counter via ethtool.

I have read the datasheeet, and with Jeffrey's detailed explaination, I
do know that this number might be higher than the actually drops I'm
experiencing.


> While we can agree that the MPC are the actual dropped packets and
> could eaily be be used in the fifo overflow count since the packets
> were really dropped.

Well, then I think we should keep MPC as drops, and use the fifo_errors
as an fifo overflow indication containing RNBC count.


> > I think that both MPC and RNBC should be stored in rx_fifo_errors
> > (and of cause still keeping them seperate to ethtool -S).
>
> This would count RNBC packets as packets that the stack did not
> process, which it did.  The MPC packets were not processed by the
> stack and should be counted as dropped.  As you point out, both counts
> are available via ethtool -S.
> 
> >I'll post two patches with these changes tomorrow, for you evaluation.
>
> Thanks, we look forward to see them.

I'll keep it to one patch (with an extra comment reflecting this
disscussion), as you have convinced me that the MPC should stay as
"rx_missed", as this is presented to userspace as a positive drop.


-- 
Med venlig hilsen / Best regards
  Jesper Brouer
  ComX Networks A/S
  Linux Network developer
  Cand. Scient Datalog / MSc.
  Author of http://adsl-optimizer.dk
  LinkedIn: http://www.linkedin.com/in/brouer

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