linux-kernel - Re: [PATCH v3] Drop Tx network packet when Tx TmFIFO is full

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Date: Fri, 12 Jan 2024 17:21:40 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Liming Sun <limings@...dia.com>
cc: Vadim Pasternak <vadimp@...dia.com>, 
    David Thompson <davthompson@...dia.com>, 
    Hans de Goede <hdegoede@...hat.com>, Mark Gross <markgross@...nel.org>, 
    Dan Carpenter <dan.carpenter@...aro.org>, 
    platform-driver-x86@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] Drop Tx network packet when Tx TmFIFO is full

On Thu, 11 Jan 2024, Liming Sun wrote:

> Starting from Linux 5.16 kernel, Tx timeout mechanism was added
> in the virtio_net driver which prints the "Tx timeout" warning
> message when a packet stays in Tx queue for too long. Below is an
> example of the reported message:
> 
> "[494105.316739] virtio_net virtio1 tmfifo_net0: TX timeout on
> queue: 0, sq: output.0, vq: 0×1, name: output.0, usecs since
> last trans: 3079892256".
> 
> This issue could happen when external host driver which drains the
> FIFO is restared, stopped or upgraded. To avoid such confusing
> "Tx timeout" messages, this commit adds logic to drop the outstanding
> Tx packet if it's not able to transmit in two seconds due to Tx FIFO
> full, which can be considered as congestion or out-of-resource drop.
> 
> This commit also handles the special case that the packet is half-
> transmitted into the Tx FIFO. In such case, the packet is discarded
> with remaining length stored in vring->rem_padding. So paddings with
> zeros can be sent out when Tx space is available to maintain the
> integrity of the packet format. The padded packet will be dropped on
> the receiving side.
> 
> Signed-off-by: Liming Sun <limings@...dia.com>
> ---
> v2->v3:
>   Updates for Ilpo's comments:
>   - Revises commit message to avoid confusion.
> v2: Fixed formatting warning
> v1: Initial version

Thanks, the commit message makes much more sense now!

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.