netdev - Re: [net 1/3] ixgbe: Fix issues with SR-IOV loopback when flow control is disabled

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Message-Id: <20120319.173801.655596594881567295.davem@davemloft.net>
Date:	Mon, 19 Mar 2012 17:38:01 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	jeffrey.t.kirsher@...el.com
Cc:	alexander.h.duyck@...el.com, netdev@...r.kernel.org,
	gospo@...hat.com, sassmann@...hat.com
Subject: Re: [net 1/3] ixgbe: Fix issues with SR-IOV loopback when flow
 control is disabled

From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Date: Sat, 17 Mar 2012 02:07:34 -0700

> From: Alexander Duyck <alexander.h.duyck@...el.com>
> 
> This patch allows us to avoid a Tx hang when SR-IOV is enabled.  This hang
> can be triggered by sending small packets at a rate that was triggering Rx
> missed errors from the adapter while the internal Tx switch and at least
> one VF are enabled.
> 
> This was all due to the fact that under heavy stress the Rx FIFO never
> drained below the flow control high water mark.  This resulted in the Tx
> FIFO being head of line blocked due to the fact that it relies on the flow
> control high water mark to determine when it is acceptable for the Tx to
> place a packet in the Rx FIFO.
> 
> The resolution for this is to set the FCRTH value to the RXPBSIZE - 32 so
> that even if the ring is almost completely full we can still place Tx
> packets on the Rx ring and drop incoming Rx traffic if we do not have
> sufficient space available in the Rx FIFO.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> Tested-by: Sibai Li <sibai.li@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

Applied.
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