netdev - Re: [PATCH v2 net-next 2/5] net-smnp: reorganize SNMP fast path variables

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Date: Tue, 17 Oct 2023 20:10:21 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Coco Li <lixiaoyan@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Mubashir Adnan Qureshi <mubashirq@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org, Chao Wu <wwchao@...gle.com>, 
	Wei Wang <weiwan@...gle.com>, David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH v2 net-next 2/5] net-smnp: reorganize SNMP fast path variables

On Tue, Oct 17, 2023 at 3:57 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> On Tue, Oct 17, 2023 at 01:47:13AM +0000, Coco Li wrote:
> > From: Chao Wu <wwchao@...gle.com>
> >
> > Reorganize fast path variables on tx-txrx-rx order.
> > Fast path cacheline ends afer LINUX_MIB_DELAYEDACKLOCKED.
> > There are only read-write variables here.
> >
> > Below data generated with pahole on x86 architecture.
> >
> > Fast path variables span cache lines before change: 12
> > Fast path variables span cache lines after change: 2
>
> As i pointed out for the first version, this is a UAPI file.
>
> Please could you add some justification that this does not cause any
> UAPI changes. Will old user space binaries still work after this?
>
> Thanks
>         Andrew

I do not think the particular order is really UAPI. Not sure why they
were pushed in uapi in the first place.

Kernel exports these counters with a leading line with the names of the metrics.

We already in the past added fields and nothing broke.

So the answer is : user space binaries not ignoring the names of the
metrics will work as before.

nstat is one of the standard binary.