netdev - Re: [PATCH v3 net-next] pktgen: introduce 'rx' mode

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Date:	Sat, 2 May 2015 18:46:25 +0200
From:	Jesper Dangaard Brouer <brouer@...hat.com>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	brouer@...hat.com, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	Robert Olsson <robert@...julf.net>,
	Ben Greear <greearb@...delatech.com>
Subject: Re: [PATCH v3 net-next] pktgen: introduce 'rx' mode

On Sat, 02 May 2015 09:01:27 -0700
Alexei Starovoitov <ast@...mgrid.com> wrote:

> On 5/2/15 1:46 AM, Jesper Dangaard Brouer wrote:
> > On Thu, 30 Apr 2015 22:12:10 -0700
> > Alexei Starovoitov <ast@...mgrid.com> wrote:
> >
> >> Introduce 'RX' mode for pktgen which generates the packets
> >> using familiar pktgen commands, but feeds them into
> >> netif_receive_skb() instead of ndo_start_xmit().
> >>
> >> It is designed to test netif_receive_skb and ingress qdisc
> >> performace only. Make sure to understand how it works before
> >> using it for other rx benchmarking.
> >
> > Hi Alexei
> >
> > First of all I love the idea of modifying pktgen to performance test
> > the RX path.
> >
> > I'm not sure the simple "rx" flag is a good "name".  It likely
> > conflicts with other work where pktgen can receive it own packets, e.g.
> > https://people.kth.se/~danieltt/pktgen/ or Ben Greer's solution.
> >
> > In your patch several things are not pktgen "compliant":
> >   1. Flags in pktgen are normally in upper-case "RX"
> >   2. Flags also require a disable "!RX" option
> >   3. You didn't add the flag to list of supported flags
> >   4. You don't output if the flag is enabled
> >   5. You didn't update the documentation (Documentation/networking/pktgen.txt)
> 
> It's actually not a flag, because it cannot be disabled by design.
> It cannot be flipped back and forth, because it affects what other
> real flags can be applied. It's a _mode_.
> I don't see yet how I can safely switch this mode back into tx while
> things are running. It would need a whole new mechanism of stopping
> things and so on. I wanted to start simple.
> For 5, yeah, agree, need to update the doc.
> As far as name, I don't have preferences. Will 'stack_inject' sound
> better? I can respin with that name if you like, but disabling it on
> the fly is a major change. I'd rather do it in small steps.

Okay, I guess it makes sense as a "mode".

Calling it "stack_inject" is fairly descriptive, but I also like
Daniel's idea of option "xmit_mode [rx|tx]".

I would not allow it to be reconfigured on the fly, but only when the
test/thread is stopped (!pkt_dev->running), allow re-configuring back
to "TX" mode.  Although, removing (and free) the entire pkt_dev, would
implicitly reset it back.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer
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