netdev - Re: [PATCH net-next v2 2/3] net: dsa: add Arrow SpeedChips XRS700x driver

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Message-ID: <20201127155135.5beb3106@kicinski-fedora-pc1c0hjn.DHCP.thefacebook.com>
Date:   Fri, 27 Nov 2020 15:51:35 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     George McCollister <george.mccollister@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        "open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>
Subject: Re: [PATCH net-next v2 2/3] net: dsa: add Arrow SpeedChips XRS700x
 driver

On Sat, 28 Nov 2020 01:21:40 +0200 Vladimir Oltean wrote:
> On Fri, Nov 27, 2020 at 01:37:53PM -0800, Jakub Kicinski wrote:
> > High speed systems are often eventually consistent. Either because
> > stats are gathered from HW periodically by the FW, or RCU grace period
> > has to expire, or workqueue has to run, etc. etc. I know it's annoying
> > for writing tests but it's manageable.  
> 
> Out of curiosity, what does a test writer need to do to get out of the
> "eventual consistency" conundrum in a portable way and answer the
> question "has my packet not been received by the interface or has the
> counter just not updated"?

Retry for a reasonable amount of time for the system state to converge.
E.g. bpftool_prog_list_wait() in selftests/bpf/test_offloads.py, or
check_tables() in selftests/drivers/net/udp_tunnel_nic.sh.

Sadly I was too lazy to open source the driver tests we built at
Netronome.