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Date:	Mon, 19 Mar 2012 17:38:01 -0400 (EDT)
From:	David Miller <>
Subject: Re: [net 1/3] ixgbe: Fix issues with SR-IOV loopback when flow
 control is disabled

From: Jeff Kirsher <>
Date: Sat, 17 Mar 2012 02:07:34 -0700

> From: Alexander Duyck <>
> 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 <>
> Tested-by: Sibai Li <>
> Signed-off-by: Jeff Kirsher <>

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