netdev - Re: [PATCH net] bareudp: Fix device stats updates.

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Message-ID: <CANn89iJ-K82U8mSNW_NGQtzKr70weHrWiFqnBEj-ehhWRHveFg@mail.gmail.com>
Date: Fri, 6 Sep 2024 14:47:15 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Guillaume Nault <gnault@...hat.com>
Cc: Jakub Kicinski <kuba@...nel.org>, David Miller <davem@...emloft.net>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, 
	Martin Varghese <martin.varghese@...ia.com>, Willem de Bruijn <willemb@...gle.com>, 
	David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH net] bareudp: Fix device stats updates.

On Fri, Sep 6, 2024 at 12:42 PM Guillaume Nault <gnault@...hat.com> wrote:
>
> On Wed, Sep 04, 2024 at 02:48:39PM -0700, Jakub Kicinski wrote:
> > On Wed, 4 Sep 2024 19:54:40 +0200 Guillaume Nault wrote:
> > > In this context, I feel that dstats is now just a mix of tstats and
> > > core_stats.
> >
> > I don't know the full background but:
> >
> >  *    @core_stats:    core networking counters,
> >  *                    do not use this in drivers
>
> Hum, I didn't realise that :/.
>
> I'd really like to understand why drivers shouldn't use core_stats.
>
> I mean, what makes driver and core networking counters so different
> that they need to be handled in two different ways (but finally merged
> together when exporting stats to user space)?
>
> Does that prevent any contention on the counters or optimise cache line
> access? I can't see how, so I'm probably missing something important
> here.

Some archeology might help.

Before we had tracing, having separate fields could help for diagnostics.

commit caf586e5f23cebb2a68cbaf288d59dbbf2d74052
Author: Eric Dumazet <eric.dumazet@...il.com>
Date:   Thu Sep 30 21:06:55 2010 +0000

    net: add a core netdev->rx_dropped counter

    In various situations, a device provides a packet to our stack and we
    drop it before it enters protocol stack :
    - softnet backlog full (accounted in /proc/net/softnet_stat)
    - bad vlan tag (not accounted)
    - unknown/unregistered protocol (not accounted)

    We can handle a per-device counter of such dropped frames at core level,
    and automatically adds it to the device provided stats (rx_dropped), so
    that standard tools can be used (ifconfig, ip link, cat /proc/net/dev)

    This is a generalization of commit 8990f468a (net: rx_dropped
    accounting), thus reverting it.

    Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>