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 v2 2/2] net: bcmgenet: flatten frames that cannot fit the ring
Date: Mon, 9 Nov 2026 14:14:31 -0800 [thread overview]
Message-ID: <229e94bd-28ff-443f-9667-f8f304a2fb0c@broadcom.com> (raw)
In-Reply-To: <20261109-nb-genet-txq-thld-net-v2-2-efd8f4be96f2@tipi-net.de>
On 11/9/26 13:53, Nicolai Buchwitz wrote:
> bcmgenet_xmit() wants one descriptor more than the frame needs. A 31
> fragment frame needs 32 descriptors, so it is refused on a 32 descriptor
> ring, even if the ring is empty.
>
> As a result nothing is in flight which could wake the queue again. The
> watchdog can only hand the same frame back, therefore the queue stays
> stopped.
>
> This needs CONFIG_MAX_SKB_FRAGS >= 31 and a sender which fragments that
> finely, for example MSG_ZEROCOPY.
>
> Linearize those frames instead.
>
> 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>
--
Florian
prev parent reply other threads:[~2026-11-09 22:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-09 21:53 [PATCH net v2 0/2] net: bcmgenet: fix tx stalls on 32 descriptor rings Nicolai Buchwitz
2026-11-09 21:53 ` [PATCH net v2 1/2] net: bcmgenet: cap the Tx queue threshold at the ring size Nicolai Buchwitz
2026-11-09 21:53 ` [PATCH net v2 2/2] net: bcmgenet: flatten frames that cannot fit the ring Nicolai Buchwitz
2026-11-09 22:14 ` Florian Fainelli [this message]
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