netdev - Re: [PATCH v4 net-next RFC] net: Generic XDP

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Date:   Wed, 19 Apr 2017 10:17:56 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andy Gospodarek <andy@...yhouse.net>
Cc:     David Miller <davem@...emloft.net>, michael.chan@...adcom.com,
        netdev@...r.kernel.org, xdp-newbies@...r.kernel.org
Subject: Re: [PATCH v4 net-next RFC] net: Generic XDP

On Wed, Apr 19, 2017 at 10:29:03AM -0400, Andy Gospodarek wrote:
> 
> I ran this on top of a card that uses the bnxt_en driver on a desktop
> class system with an i7-6700 CPU @ 3.40GHz, sending a single stream of
> UDP traffic with flow control disabled and saw the following (all stats
> in Million PPS).
> 
>                 xdp1                xdp2            xdp_tx_tunnel
> Generic XDP      7.8    5.5 (1.3 actual)         4.6 (1.1 actual)
> Optimized XDP   11.7		     9.7                      4.6

Nice! Thanks for testing.

> One thing to note is that the Generic XDP case shows some different
> results for reported by the application vs actual (seen on the wire).  I
> did not debug where the drops are happening and what counter needs to be
> incremented to note this -- I'll add that to my TODO list.  The
> Optimized XDP case does not have a difference in reported vs actual
> frames on the wire.

The missed packets are probably due to xmit queue being full.
We need 'xdp_tx_full' counter in:
+       if (free_skb) {
+               trace_xdp_exception(dev, xdp_prog, XDP_TX);
+               kfree_skb(skb);
+       }
like in-driver xdp does.
It's surprising that tx becomes full so often. May be bnxt specific behavior?

> I agree with all those who have asserted that this is great tool for
> those that want to get started with XDP but do not have hardware, so I'd
> say it's ready to have the 'RFC' tag dropped.  Thanks for pushing this
> forward, Dave!  :-)

+1