netdev - Re: [PATCH] vmxnet3: Fix inconsistent LRO state after initialization

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Date:	Mon, 16 May 2011 10:14:44 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Thomas Jarosch <thomas.jarosch@...ra2net.com>
Cc:	netdev@...r.kernel.org, Shreyas Bhatewara <sbhatewara@...are.com>
Subject: Re: [PATCH] vmxnet3: Fix inconsistent LRO state after
 initialization

On Mon, 16 May 2011 18:28:15 +0200
Thomas Jarosch <thomas.jarosch@...ra2net.com> wrote:

> During initialization of vmxnet3, the state of LRO
> gets out of sync with netdev->features.
> 
> This leads to very poor TCP performance in a IP forwarding
> setup and is hitting many VMware users.
> 
> Simplified call sequence:
> 1. vmxnet3_declare_features() initializes "adapter->lro" to true.
> 
> 2. The kernel automatically disables LRO if IP forwarding is enabled,
> so vmxnet3_set_flags() gets called. This also updates netdev->features.
> 
> 3. Now vmxnet3_setup_driver_shared() is called. "adapter->lro" is still
> set to true and LRO gets enabled again, even though
> netdev->features shows it's disabled.
> 
> Fix it by updating "adapter->lro", too.
> 
> 
> The private vmxnet3 adapter flags are scheduled for removal
> in net-next, see commit a0d2730c9571aeba793cb5d3009094ee1d8fda35
> "net: vmxnet3: convert to hw_features".
> 
> Patch applies to 2.6.37 / 2.6.38 and 2.6.39-rc6.
> 
> Please CC: comments.
> 
> Signed-off-by: Thomas Jarosch <thomas.jarosch@...ra2net.com>
> 
> diff -u -r -p linux-2.6.37.i686/drivers/net/vmxnet3/vmxnet3_ethtool.c linux-2.6.37.lro/drivers/net/vmxnet3/vmxnet3_ethtool.c
> --- linux-2.6.37.i686/drivers/net/vmxnet3/vmxnet3_ethtool.c	2011-05-16 17:43:26.652081801 +0200
> +++ linux-2.6.37.lro/drivers/net/vmxnet3/vmxnet3_ethtool.c	2011-05-16 17:47:52.784081802 +0200
> @@ -287,6 +287,9 @@ vmxnet3_set_flags(struct net_device *net
>  		/* toggle the LRO feature*/
>  		netdev->features ^= NETIF_F_LRO;
>  
> +		/* Update private LRO flag */
> +		adapter->lro = lro_requested;
> +
>  		/* update harware LRO capability accordingly */
>  		if (lro_requested)
>  			adapter->shared->devRead.misc.uptFeatures |=

Thanks for finding this. Vyatta ended up changing the default of adapter->lro
to workaround just this problem

Acked-by: Stephen Hemminger <shemminger@...tta.com>


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