netdev - Re: [RFC v4 1/2] iwlwifi: pcie: allow to build an A-MSDU using TSO core

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Date:	Thu, 22 Oct 2015 14:29:39 +0000
From:	"Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>
To:	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Sharon, Sara" <sara.sharon@...el.com>,
	"ido@...ery.com" <ido@...ery.com>
Subject: Re: [RFC v4 1/2] iwlwifi: pcie: allow to build an A-MSDU using TSO
 core



On 10/22/2015 04:08 PM, Grumbach, Emmanuel wrote:
> When the op_mode sends an skb whose payload is bigger than
> MSS, PCIe will create an A-MSDU out of it. PCIe assumes
> that the skb that is coming from the op_mode can fit in one
> A-MSDU. It is the op_mode's responsibility to make sure
> that this guarantee holds.
> 
> Additional headers need to be built for the subframes.
> The TSO core code takes care of the IP / TCP headers and
> the driver takes care of the 802.11 subframe headers.
> 
> These headers are stored on a per-cpu page that is re-used
> for all the packets handled on that same CPU. Each skb
> holds a reference to that page and releases the page when
> it is reclaimed. When the page gets full, it is released
> and a new one is allocated.
> 
> Since any SKB that doesn't go through the fast-xmit path
> of mac80211 will be segmented, we can assume here that the
> packet is not WEP / TKIP and has a proper SNAP header.
> 
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@...el.com>
> ---
> v4: * Create a helper to free the skb's ref to the hdr page
>     * add comment on that clarifies that the headers fit in a page
>     * return -ENOMEM if the per_cpu variable allocation failed
>     * don't zero the per_cpu struct after allocation
> ---

Meh... Someone internally founds a few bugs... Don't waste your time on
this one. V5 will come later tonight.
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