Re: [PATCH V2 net-next 1/6] ethtool: add support to set/get tx copybreak buf size via ethtool

On 2021/9/25 7:05, Michal Kubecek wrote:

On Fri, Sep 24, 2021 at 10:29:54PM +0800, Guangbin Huang wrote:

quoted

From: Hao Chen <redacted>

Add support for ethtool to set/get tx copybreak buf size.

Signed-off-by: Hao Chen <redacted>
Signed-off-by: Guangbin Huang <redacted>
---
  Documentation/networking/ethtool-netlink.rst | 24 ++++++++++++++++++++
  include/uapi/linux/ethtool.h                 |  1 +
  net/ethtool/common.c                         |  1 +
  net/ethtool/ioctl.c                          |  1 +
  4 files changed, 27 insertions(+)

diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/networking/ethtool-netlink.rst
index d9b55b7a1a4d..a47b0255aaf9 100644
--- a/Documentation/networking/ethtool-netlink.rst
+++ b/Documentation/networking/ethtool-netlink.rst

@@ -1521,6 +1521,30 @@ Kernel response contents:
    ``ETHTOOL_A_PHC_VCLOCKS_INDEX``       s32     PHC index array
    ====================================  ======  ==========================
  
+TUNABLE_SET
+===========
+
+Request contents:
+
+  =====================================  ======  ==========================
+  ``ETHTOOL_TX_COPYBREAK_BUF_SIZE``      u32     buf size for tx copybreak
+  =====================================  ======  ==========================
+
+Tx copybreak buf size is used for tx copybreak feature, the feature is used
+for small size packet or frag. It adds a queue based tx shared bounce buffer
+to memcpy the small packet when the len of xmitted skb is below tx_copybreak
+(value to distinguish small size and normal size), and reduce the overhead
+of dma map and unmap when IOMMU is on.
+
+TUNABLE_GET
+===========
+
+Kernel response contents:
+
+  ====================================  ======  ==========================
+  ``ETHTOOL_TX_COPYBREAK_BUF_SIZE``     u32     buf size for tx copybreak
+  ====================================  ======  ==========================

I have to repeat my concerns expressed in

   https://lore.kernel.org/netdev/20210826072618.2lu6spapkzdcuhyv@lion.mk-sys.cz (local)

and earlier in more details in

   https://lore.kernel.org/netdev/20200325164958.GZ31519@unicorn.suse.cz (local)

That being said, I don't understand why this patch adds description of
two new message types to the documentation of ethtool netlink API but it
does not actually add them to the API. Instead, it adds the new tunable
to ioctl API.

Michal

Hi Michal, thanks for your opinion.
Is there any documentation for ioctl API? We didn't find it.
Or we add a new documentation of ioctl API for the new tunable?

Guangbin