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Date:   Mon, 24 Jan 2022 09:29:24 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Brian Vazquez <brianvv@google.com>
Cc:     Jeffrey Ji <jeffreyjilinux@gmail.com>,
        Eric Dumazet <edumazet@google.com>,
        "David S . Miller" <davem@davemloft.net>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        jeffreyji <jeffreyji@google.com>
Subject: Re: [PATCH net-next] net-core: add InMacErrors counter
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On Mon, 24 Jan 2022 09:13:12 -0800 Brian Vazquez wrote:
> On Fri, Jan 21, 2022 at 7:41 PM Jakub Kicinski <kuba@kernel.org> wrote:
> > On Sat, 22 Jan 2022 00:03:01 +0000 Jeffrey Ji wrote:  
> > > From: jeffreyji <jeffreyji@google.com>
> > >
> > > Increment InMacErrors counter when packet dropped due to incorrect dest
> > > MAC addr.
> > >
> > > example output from nstat:
> > > \~# nstat -z "*InMac*"
> > > \#kernel
> > > Ip6InMacErrors                  0                  0.0
> > > IpExtInMacErrors                1                  0.0
> > >
> > > Tested: Created 2 netns, sent 1 packet using trafgen from 1 to the other
> > > with "{eth(daddr=$INCORRECT_MAC...}", verified that nstat showed the
> > > counter was incremented.
> > >
> > > Signed-off-by: jeffreyji <jeffreyji@google.com>  
> >
> > How about we use the new kfree_skb_reason() instead to avoid allocating
> > per-netns memory the stats?  
> 
> I'm not too familiar with the new kfree_skb_reason , but my
> understanding is that it needs either the drop_monitor  or ebpf to get
> the reason from the tracepoint, right? This is not too different from
> using perf tool to find where the pkt is being dropped.
> 
> The idea here was to have a high level metric that is easier to find
> for users that have less expertise on using more advance tools.

That much it's understood, but it's a trade off. This drop point
existed for 20 years, why do we need to consume extra memory now?