From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v9] tilegx network driver: initial support
Date: Wed, 06 Jun 2012 20:10:23 +0200
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References: <201205201636.q4KGaoA3003845@farm-0027.internal.tilera.com>
	 <20120520.165546.1211013675964130504.davem@davemloft.net>
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	 <20120524.003148.700603156196416506.davem@davemloft.net>
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Cc: bhutchings@solarflare.com, arnd@arndb.de,
	David Miller <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org
To: Chris Metcalf <cmetcalf@tilera.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <201206042023.q54KNEZp003834@farm-0002.internal.tilera.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Mon, 2012-06-04 at 16:12 -0400, Chris Metcalf wrote:
> This change adds support for the tilegx network driver based on the
> GXIO IORPC support in the tilegx software stack, using the on-chip
> mPIPE packet processing engine.
> 

> +
> +/* Do "TSO" handling for egress.
> + *
> + * Normally drivers set NETIF_F_TSO only to support hardware TSO;
> + * otherwise the stack uses scatter-gather to implement GSO in software.
> + * On our testing, enabling GSO support (via NETIF_F_SG) drops network
> + * performance down to around 7.5 Gbps on the 10G interfaces, although
> + * also dropping cpu utilization way down, to under 8%.  But
> + * implementing "TSO" in the driver brings performance back up to line
> + * rate, while dropping cpu usage even further, to less than 4%.  In
> + * practice, profiling of GSO shows that skb_segment() is what causes
> + * the performance overheads; we benefit in the driver from using
> + * preallocated memory to duplicate the TCP/IP headers.
> + */

All this stuff cost about 300 lines of code in this driver, without IPv6
support.

I am pretty sure this performance problem should be solved in net/{core|
ipv4|ipv6} instead

What TCP performance do you get with TSO/GSO and SG off ?