Subject: Re: [PATCH] e1000e: stop unnecessary polling when using msi-x

From: Alexander Duyck <[email-masked]>
Date: Thu, 18 Jun 2009 15:06:36 -0700

Andy Gospodarek wrote:
> The last hunk of this commit:
> 
>     commit 12d04a3c12b420f23398b4d650127642469a60a6
>     Author: Alexander Duyck <[email-masked]>
>     Date:   Wed Mar 25 22:05:03 2009 +0000
> 
>         e1000e: commonize tx cleanup routine to match e1000 & igb
> 
> changed the logic for determining if we should call napi_complete or
> not at then end of a napi poll.
> 
> If the NIC is using MSI-X with no work to do in ->poll, net_rx_action
> can just spin indefinitely on older kernels and for 2 jiffies on newer
> kernels since napi_complete is never called and budget isn't
> decremented.
> 
> Discovered and verified while testing driver backport to an older
> kernel.
> 
> Signed-off-by: Andy Gospodarek <[email-masked]>
> 
> ---
> 
>  netdev.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
> index 677f604..679885a 100644
> --- a/drivers/net/e1000e/netdev.c
> +++ b/drivers/net/e1000e/netdev.c
> @@ -1997,7 +1997,7 @@ static int e1000_clean(struct napi_struct *napi, int budget)
>  	struct e1000_adapter *adapter = container_of(napi, struct e1000_adapter, napi);
>  	struct e1000_hw *hw = &adapter->hw;
>  	struct net_device *poll_dev = adapter->netdev;
> -	int tx_cleaned = 0, work_done = 0;
> +	int tx_cleaned = 1, work_done = 0;
>  
>  	adapter = netdev_priv(poll_dev);
> 
> 
This is most certainly a bug, and the fix is correct.  The logic for 
tx_cleaned is supposed to default to true in the event that there are no 
   tx queues cleaned as part of the polling routine.

Acked-by: Alexander Duyck <[email-masked]>