netdev - Re: [RFC] r8169 : why SG / TX checksum are default disabled

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Message-ID: <20120717234037.GA26972@electric-eye.fr.zoreil.com>
Date:	Wed, 18 Jul 2012 01:40:37 +0200
From:	Francois Romieu <romieu@...zoreil.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, Hayes Wang <hayeswang@...ltek.com>
Subject: Re: [RFC] r8169 : why SG / TX checksum are default disabled

Eric Dumazet <eric.dumazet@...il.com> :
[...]
> I was wondering why Scatter Gather (NETIF_F_SG) and TX checksum
> (NETIF_F_IP_CSUM) were disabled by default on r8169.

It was not unconditionally stable. For a number of reasons:
- incompatibility with jumbo frames.
  rtl_chip_infos now allows to take care of it
- lack of support for chipset dependent Tx descriptor 
  rtl_tx_desc_info handles it. There are yet a few unused ipv6 bits. No idea
  how useable they are.
- some false alarms due to different issues and probably some others
  I could hunt for in the archives.

> Couldnt we enable them by default, maybe for a whitelist of "good"
> nics ?

Sure.

Hayes, should we not add into the kernel driver something similar to
the rtl8168_start_xmit::skb_checksum_help stuff in Realtek's 8168 driver ?
There seems to be a bug for (skb->len < 60 && RTL_GIGA_MAC_VER_34.

> (I found that activating them with ethtool automatically enables GSO,
>  and performance with GSO is not good)

It's still an improvement though, isn't it ?

-- 
Ueimor
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