netdev - Re: Getting physical packet counts with LRO enabled with ixgbe?

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Date:	Wed, 23 Sep 2009 11:50:34 -0700
From:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	NetDev <netdev@...r.kernel.org>
Subject: Re: Getting physical packet counts with LRO enabled with ixgbe?

On Wed, 2009-09-23 at 11:46 -0700, Ben Greear wrote:
> On 09/23/2009 11:32 AM, Peter P Waskiewicz Jr wrote:
> > On Wed, 2009-09-23 at 09:40 -0700, Ben Greear wrote:
> >> I notice that with LRO enabled, the interface stats count the LRO'd pkts,
> >> not the physical ones on the wire.
> >>
> >> I also tried using ethtool -S, but it seems those counters are the same.
> >>
> >> Is there any way to get the actual rx/tx packet count on the wire?
> >>
> >
> > Depending on which device you're using ixgbe with, there are slightly
> > different registers to get what you want.
> >
> > The only suggestion I have for you though is to refer to the datasheets
> > for each device on our SourceForge site (e1000.sf.net).  Some of the
> > relevant counters to look at are PRC64, PRC127, etc, and GPRC/GPTC.  For
> > the per-queue stuff, you'll need to look at the TQSMR and RQSMR mapping
> > registers.  Let me know if you need assistance in using these registers.
> 
> Thanks, I'll look at the data-sheet.
> 
> I don't care about per-queue stats at this time, just
> over-all NIC stats.
> 
> >> Also, for the rx/tx bytes, I assume that isn't counting the protocol headers
> >> for the physical pkts that have been merged into a single LRO packet.  Is
> >> there any way to get the wire stats for bytes as well?
> >
> > The counters for per-byte are purely software-based, so if the packet is
> > LRO'd, you can probably do some somewhat trivial math with the MTU to
> > find the actual wire stats.  But we only compute what we pass to the
> > stack, so it'd be the LRO'd packet.
> 
> That's a bummer.  I'm guessing you might get close to right on average with some
> trivial math, but if someone is sending you pkts with size of 1000 and
> your MTU is 1500, would there be any way to tell that the pkts were originally
> 1000 bytes instead of 1500?

Good point.

> Next time you guys re-compile your hardware, please consider adding byte counters :)

On 10G adapters, byte counters can skyrocket quickly, so we'd need to
read them often to avoid them wrapping.  But I will forward your request
to our HW design folks and see if they have other ideas to implement
these counters and make them efficient.

Cheers,
-PJ

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