Re: [PATCH V4 net-next 1/6] ethtool: add support to set/get tx copybreak buf size via ethtool

On 2021/10/14 21:58, Eric Dumazet wrote:

On 10/14/21 4:39 AM, Guangbin Huang wrote:

quoted

From: Hao Chen <redacted>

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

What is the unit ?

Frankly, having to size the 'buffer' based on number of slots in TX ring buffer
is not good.

What happens later when/if ethtool -G tx xxxxx' is trying
to change number of slots ?

The 'tx copybreak' should instead give a number of bytes per TX ring slot.

Eg, 128 or 256 bytes.

This is very similar to what drivers using net/core/tso.c do.

They usually use TSO_HEADER_SIZE for this.

Hi Eric,
The unit is bytes.

Tx copybreak buf is a queue based tx shared bounce buffer and it is allocated
based on page size, not based on slot numbers. When the len of xmitted skb is
below tx_copybreak, tx copybreak buf will share buffer of specific size(slot size)
for tx to memcpy the small packet.

So, what you mentioned seems not related to this patch.

quoted

Signed-off-by: Hao Chen <redacted>
Signed-off-by: Guangbin Huang <redacted>
---
  include/uapi/linux/ethtool.h | 1 +
  net/ethtool/common.c         | 1 +
  net/ethtool/ioctl.c          | 1 +
  3 files changed, 3 insertions(+)

diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
index a2223b685451..7bc4b8def12c 100644
--- a/include/uapi/linux/ethtool.h
+++ b/include/uapi/linux/ethtool.h

@@ -231,6 +231,7 @@ enum tunable_id {
  	ETHTOOL_RX_COPYBREAK,
  	ETHTOOL_TX_COPYBREAK,
  	ETHTOOL_PFC_PREVENTION_TOUT, /* timeout in msecs */
+	ETHTOOL_TX_COPYBREAK_BUF_SIZE,
  	/*
  	 * Add your fresh new tunable attribute above and remember to update
  	 * tunable_strings[] in net/ethtool/common.c

diff --git a/net/ethtool/common.c b/net/ethtool/common.c
index c63e0739dc6a..0c5210015911 100644
--- a/net/ethtool/common.c
+++ b/net/ethtool/common.c

@@ -89,6 +89,7 @@ tunable_strings[__ETHTOOL_TUNABLE_COUNT][ETH_GSTRING_LEN] = {
  	[ETHTOOL_RX_COPYBREAK]	= "rx-copybreak",
  	[ETHTOOL_TX_COPYBREAK]	= "tx-copybreak",
  	[ETHTOOL_PFC_PREVENTION_TOUT] = "pfc-prevention-tout",
+	[ETHTOOL_TX_COPYBREAK_BUF_SIZE] = "tx-copybreak-buf-size",
  };
  
  const char

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index bf6e8c2f9bf7..617ebc4183d9 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c

@@ -2383,6 +2383,7 @@ static int ethtool_tunable_valid(const struct ethtool_tunable *tuna)
  	switch (tuna->id) {
  	case ETHTOOL_RX_COPYBREAK:
  	case ETHTOOL_TX_COPYBREAK:
+	case ETHTOOL_TX_COPYBREAK_BUF_SIZE:
  		if (tuna->len != sizeof(u32) ||
  		    tuna->type_id != ETHTOOL_TUNABLE_U32)
  			return -EINVAL;

.