From: Florian Fainelli <florian.fainelli@broadcom.com>
To: Nicolai Buchwitz <nb@tipi-net.de>,
Doug Berger <opendmb@gmail.com>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@kernel.org>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>
Cc: Justin Chen <justin.chen@broadcom.com>,
Broadcom internal kernel review list
<bcm-kernel-feedback-list@broadcom.com>,
Nikolay Aleksandrov <razor@blackwall.org>,
Jason Xing <kerneljasonxing@gmail.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: bcmgenet: cap the Tx queue threshold at the ring size
Date: Fri, 6 Nov 2026 16:14:05 -0800 [thread overview]
Message-ID: <1b33c10e-fa25-427a-92a6-d26669712f09@broadcom.com> (raw)
In-Reply-To: <20261106-nb-genet-txq-thld-net-v1-1-53bbac647b71@tipi-net.de>
On 11/6/2026 6:10 AM, Nicolai Buchwitz wrote:
> A Tx queue stops when MAX_SKB_FRAGS + 1 or fewer descriptors are free and
> wakes once there are more. Queues 1 to 4 hold 32 descriptors, so with
> CONFIG_MAX_SKB_FRAGS at 31 they would need 33 to wake. As a result the
> first packet stops the queue and it stays stopped:
>
> eth0: NETDEV WATCHDOG: CPU: 0: transmit queue 3 timed out 2004 ms
> eth0: NETDEV WATCHDOG: CPU: 1: transmit queue 4 timed out 2004 ms
>
> On a Raspberry Pi CM4 only queue 0 carried traffic afterwards. The other
> four counted an error on nearly every packet.
>
> Fix this and cap the threshold at what the ring can free.
>
> Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")
> Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Eventually we will have to decide what to do with those other queues :D
--
Florian
prev parent reply other threads:[~2026-11-07 0:14 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-06 14:10 Nicolai Buchwitz
2026-11-07 0:14 ` Florian Fainelli [this message]
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