patches for DPDK stable branches
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From: Luca Boccassi <>
To: Long Li <>,
Cc: Long Li <>,
	Stephen Hemminger <>
Subject: Re: [dpdk-stable] [PATCH 19.11 2/2] net/netvsc: control use of external mbuf on Rx
Date: Thu, 10 Dec 2020 18:28:50 +0000
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, 2020-12-09 at 16:27 -0800, Long Li wrote:
> From: Long Li <>
> [ upstream commit 096b31fc0d8c989cc455c35f4d1def24a4ed6dee ]
> When receiving packets, netvsp puts data in a buffer mapped through UIO.
> Depending on packet size, netvsc may attach the buffer as an external
> mbuf. This is not a problem if this mbuf is consumed in the application,
> and the application can correctly read data out of an external mbuf.
> However, there are two problems with data in an external mbuf.
> 1. Due to the limitation of the kernel UIO implementation, physical
>    address of this external buffer is not exposed to the user-mode. If
>    this mbuf is passed to another driver, the other driver is unable to
>    map this buffer to iova.
> 2. Some DPDK applications are not aware of external mbuf, and may bug
>    when they receive an mbuf with external buffer attached.
> Introduce a driver parameter "rx_extmbuf_enable" to control if netvsc
> should use external mbuf for receiving packets. The default value is 0.
> (netvsc doesn't use external mbuf, it always allocates mbuf and copy
> data to mbuf) A non-zero value tells netvsc to attach external buffers
> to mbuf on receiving packets, thus avoid copying memory.
> Signed-off-by: Long Li <>
> ---
>  doc/guides/nics/netvsc.rst     |  8 ++++++++
>  drivers/net/netvsc/hn_ethdev.c | 10 +++++++++-
>  drivers/net/netvsc/hn_rxtx.c   |  2 +-
>  drivers/net/netvsc/hn_var.h    |  3 +++
>  4 files changed, 21 insertions(+), 2 deletions(-)

Correct me if I'm wrong, but these 2 patches look a bit more like new
features than bug fixes? It's new options for the PMD, right?

In general, we do not take new features in LTS releases. Stable means
stable - we make very few exceptions.

Is the PMD broken/unusable without these options?

Kind regards,
Luca Boccassi

  reply	other threads:[~2020-12-10 18:28 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-10  0:27 [dpdk-stable] [PATCH 19.11 1/2] net/netvsc: allow setting Rx and Tx copy break Long Li
2020-12-10  0:27 ` [dpdk-stable] [PATCH 19.11 2/2] net/netvsc: control use of external mbuf on Rx Long Li
2020-12-10 18:28   ` Luca Boccassi [this message]
2020-12-10 19:44     ` Long Li
2020-12-15 13:48       ` Luca Boccassi
2020-12-16  1:09         ` Stephen Hemminger
2020-12-16  2:16           ` Long Li

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