From: "Loke, Chetan" <Chetan.Loke@netscout.com>
To: "Eric Dumazet" <eric.dumazet@gmail.com>,
"Richard Cochran" <richardcochran@gmail.com>
Cc: "Ingo Kofler" <ikofler@edu.uni-klu.ac.at>, <netdev@vger.kernel.org>
Subject: RE: Problems obtaining software TX timestamps
Date: Thu, 9 Sep 2010 10:31:45 -0400 [thread overview]
Message-ID: <D3F292ADF945FB49B35E96C94C2061B90D19931F@nsmail.netscout.com> (raw)
In-Reply-To: <1284040958.2589.178.camel@edumazet-laptop>
> From: netdev-owner@vger.kernel.org [mailto:netdev-
> owner@vger.kernel.org] On Behalf Of Eric Dumazet
> Sent: September 09, 2010 10:03 AM
> To: Richard Cochran
> Cc: Ingo Kofler; netdev@vger.kernel.org
> Subject: Re: Problems obtaining software TX timestamps
>
> Le jeudi 09 septembre 2010 à 15:57 +0200, Richard Cochran a écrit :
> > On Thu, Sep 09, 2010 at 10:26:06AM +0200, Ingo Kofler wrote:
> > > Thank you very much for this clarification. Are there any drawbacks
> > > with this approach, e.g. performance issues? Honestly, I am just
> > > wondering why driver developers do not add this single line if it's
> > > that easy....
> >
> > Adding the line only tests one flag, so it is not a huge performance
> > hit. This fix is very recent, that is why it has not been used in MAC
> > drivers yet.
>
> Should drivers call it at start_xmit() time, or at tx completion time ?
>
> 1) start_xmit() time : Earlier than real hardware xmit (with up to 1000
> packets queued in TX ring, delay might be very large)
>
> 2) tx completion time : After real hardware xmit
> (on tg3, ethtool -c gives : tx-usecs: 72 , tx-frames: 53, so we can
> have a delay of 72 us before NIC acknowledges the frame xmit)
>
I'm not familiar w/ the code but I would think right before the Tx-descriptors are posted. That is, before a pci-write, where the Tx-queue put
ptrs are updated. Because if the NIC is overloaded then there will be some delay before the pkts are Xmit'd. But if there is a N/W TAP then we would atleast roughly know where we could start troubleshooting.
Chetan Loke
next prev parent reply other threads:[~2010-09-09 14:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-08 12:11 Problems obtaining software TX timestamps Ingo Kofler
2010-09-08 15:12 ` Eric Dumazet
2010-09-08 21:21 ` Ingo Kofler
2010-09-08 21:24 ` David Miller
2010-09-09 6:35 ` Richard Cochran
2010-09-09 8:26 ` Ingo Kofler
2010-09-09 13:57 ` Richard Cochran
2010-09-09 14:02 ` Eric Dumazet
2010-09-09 14:31 ` Loke, Chetan [this message]
2010-09-09 17:32 ` Richard Cochran
2010-09-09 18:58 ` Eric Dumazet
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