netdev - Re: [net PATCH v2] i40e/i40evf: Limit TSO to 7 descriptors for payload instead of 8 per packet

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Date:	Thu, 31 Mar 2016 15:04:38 -0700
From:	Jesse Brandeburg <jesse.brandeburg@...el.com>
To:	Alexander Duyck <aduyck@...antis.com>
Cc:	<netdev@...r.kernel.org>, <alexander.duyck@...il.com>,
	<intel-wired-lan@...ts.osuosl.org>, <jeffrey.t.kirsher@...el.com>,
	<sowmini.varadhan@...cle.com>
Subject: Re: [net PATCH v2] i40e/i40evf: Limit TSO to 7 descriptors for
 payload instead of 8 per packet

On Wed, 30 Mar 2016 16:15:37 -0700
Alexander Duyck <aduyck@...antis.com> wrote:

> This patch addresses a bug introduced based on my interpretation of the
> XL710 datasheet.  Specifically section 8.4.1 states that "A single transmit
> packet may span up to 8 buffers (up to 8 data descriptors per packet
> including both the header and payload buffers)."  It then later goes on to
> say that each segment for a TSO obeys the previous rule, however it then
> refers to TSO header and the segment payload buffers.
> 
> I believe the actual limit for fragments with TSO and a skbuff that has
> payload data in the header portion of the buffer is actually only 7
> fragments as the skb->data portion counts as 2 buffers, one for the TSO
> header, and one for a segment payload buffer.
> 
> Fixes: 2d37490b82af ("i40e/i40evf: Rewrite logic for 8 descriptor per packet check")
> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
> ---
> 
> v2: I realized that I overlooked the check in the inline function and as a
>     result we were still allowing for cases where 8 descriptors were being
>     used per packet and this would result in 9 DMA buffers.  I updated the
>     code so that we only allow 8 in the case of a single send, otherwise we
>     go into the function that walks the frags to verify each block.
> 
> I have tested this using rds-stress and it seems to run traffic without
> throwing any errors.

Looking like it is working for me too with at least the PF.

Acked-by: Jesse Brandeburg <jesse.brandeburg@...el.com>

Should also add:
Reported-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>