linux-kernel - Re: [RFC PATCH net] net/core: don't increment rx

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Date:	Tue, 26 Jan 2016 13:24:59 -0800
From:	Eric Dumazet <edumazet@...gle.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Pirko <jiri@...lanox.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Tom Herbert <tom@...bertland.com>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Veaceslav Falico <vfalico@...il.com>,
	Andy Gospodarek <gospo@...ulusnetworks.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH net] net/core: don't increment rx_dropped on inactive slaves

On Tue, Jan 26, 2016 at 1:14 PM, Jarod Wilson <jarod@...hat.com> wrote:
> On Sat, Jan 23, 2016 at 07:23:09AM -0800, Eric Dumazet wrote:
>> On Fri, 2016-01-22 at 14:11 -0500, Jarod Wilson wrote:
>>
>> > ---
>> >  net/core/dev.c | 3 +++
>> >  1 file changed, 3 insertions(+)
>> >
>> > diff --git a/net/core/dev.c b/net/core/dev.c
>> > index 8cba3d8..1354c7b 100644
>> > --- a/net/core/dev.c
>> > +++ b/net/core/dev.c
>> > @@ -4153,8 +4153,11 @@ ncls:
>> >             else
>> >                     ret = pt_prev->func(skb, skb->dev, pt_prev, orig_dev);
>> >     } else {
>> > +           if (deliver_exact)
>> > +                   goto inactive; /* bond or team inactive slave */
>> >  drop:
>> >             atomic_long_inc(&skb->dev->rx_dropped);
>> > +inactive:
>> >             kfree_skb(skb);
>> >             /* Jamal, now you will not able to escape explaining
>> >              * me how you were going to use this. :-)
>>
>> Note that if you still have a kfree_skb() instead of consume_skb(),
>> some tools will still give you a wrong signal (packet dropped ...).
>>
>> But then maybe the signal is telling some truth.
>>
>> We receive a packet, and decide to drop it because no one was willing to
>> handle it.
>>
>> Maybe someone wants to know a particular slave receives 10,000 such
>> frames per second and hurts performance with useless work.
>>
>> We should at least increment some counter and maybe dump it with
>> "ethtool -S" or something.
>
> I've been digging into ethtool -S a little bit, and am somewhat at a loss
> as to how I would wire into this. From what I've been able to figure out,
> it's entirely device-specific-ish counters spit out. On my sfc cards, I
> get rx_noskb_drops and rx_nodesc_drop_cnt output from ethtool -S, but for
> the core network stack, these are actually added up and shoved into
> rx_dropped, and no other network driver has those two individual counters.
>
> By itself, rx_dropped isn't output directly anywhere from ethtool,
> so far as I can see. And ethtool -S bondX shows absolutely nothing.
> *Should* ethtool -S be dumping all the network core stats? I have to say I
> was more than a little surprised at this:

# ip -s -s link sh dev eth0
15: eth0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc
pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 3c:97:0e:be:91:7b brd ff:ff:ff:ff:ff:ff
    RX: bytes  packets  errors  dropped overrun mcast
    0          0        0       0       0       0
    RX errors: length  crc     frame   fifo    missed
               0        0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    0          0        0       0       0       0
    TX errors: aborted fifo    window  heartbeat
               0        0       0       0

So start with the following patch :

diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index a30b78090594..7c762cf1e4d5 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -68,6 +68,8 @@ struct rtnl_link_stats64 {
        /* for cslip etc */
        __u64   rx_compressed;
        __u64   tx_compressed;
+
+       __u64   rx_nohandler;           /* packet was of no interest */
 };

 /* The struct should be in sync with struct ifmap */