netdev - Re: [RFC net-next] net: mvneta: align xdp stats naming scheme to mlx5 driver

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Message-Id: <20200218.154713.1411536344737312845.davem@davemloft.net>
Date:   Tue, 18 Feb 2020 15:47:13 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     toke@...hat.com
Cc:     kuba@...nel.org, lorenzo@...nel.org, netdev@...r.kernel.org,
        ilias.apalodimas@...aro.org, lorenzo.bianconi@...hat.com,
        andrew@...n.ch, brouer@...hat.com, dsahern@...nel.org,
        bpf@...r.kernel.org
Subject: Re: [RFC net-next] net: mvneta: align xdp stats naming scheme to
 mlx5 driver

From: Toke Høiland-Jørgensen <toke@...hat.com>
Date: Tue, 18 Feb 2020 23:23:22 +0100

> Jakub Kicinski <kuba@...nel.org> writes:
> 
>> On Tue, 18 Feb 2020 01:14:29 +0100 Lorenzo Bianconi wrote:
>>> Introduce "rx" prefix in the name scheme for xdp counters
>>> on rx path.
>>> Differentiate between XDP_TX and ndo_xdp_xmit counters
>>> 
>>> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
>>
>> Sorry for coming in late.
>>
>> I thought the ability to attach a BPF program to a fexit of another BPF
>> program will put an end to these unnecessary statistics. IOW I maintain
>> my position that there should be no ethtool stats for XDP.
>>
>> As discussed before real life BPF progs will maintain their own stats
>> at the granularity of their choosing, so we're just wasting datapath
>> cycles.
>>
>> The previous argument that the BPF prog stats are out of admin control
>> is no longer true with the fexit option (IIUC how that works).
> 
> So you're proposing an admin that wants to keep track of XDP has to
> (permantently?) attach an fexit program to every running XDP program and
> use that to keep statistics? But presumably he'd first need to discover
> that XDP is enabled; which the ethtool stats is a good hint for :)

Really, mistakes happen and a poorly implemented or inserted fexit
module should not be a reason to not have access to accurate and
working statistics for fundamental events.

I am therefore totally against requiring fexit for this functionality.
If you want more sophisticated events or custome ones, sure, but not
for this baseline stuff.

I do, however, think we need a way to turn off these counter bumps if
the user wishes to do so for maximum performance.