Message-ID: <ad4fbfcb67afcb63c34711d14459b2a183831e38.camel@sipsolutions.net>
Subject: Re: [PATCH] mac80211: optimize skb resizing
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Felix Fietkau <nbd@nbd.name>, linux-wireless@vger.kernel.org
Date:   Mon, 08 Apr 2019 14:26:49 +0200
In-Reply-To: <20190317181859.71841-1-nbd@nbd.name>
References: <20190317181859.71841-1-nbd@nbd.name>
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On Sun, 2019-03-17 at 19:18 +0100, Felix Fietkau wrote:
> When forwarding unicast packets from ethernet to batman-adv over 802.11s
> (with forwarding disabled), the typical required headroom to transmit
> encrypted packets on mt76 is 32 (802.11) + 6 (802.11s) + 8 (CCMP) +
> 2 (padding) + 6 (LLC) + 18 (batman-adv) - 14 (old ethernet header) = 58 bytes.
> 
> On systems where NET_SKB_PAD is 64 this leads to a call to pskb_expand_head
> for every packet, since mac80211 also tries to allocate 16 bytes status
> headroom for radiotap headers.
> 
> This patch fixes these unnecessary reallocations by only requiring the extra
> status headroom in ieee80211_tx_monitor()
> If however a reallocation happens before that call, the status headroom gets
> added there as well, in order to avoid double reallocation.
> 
> The patch also cleans up the code by moving the headroom calculation to
> ieee80211_skb_resize.

This doesn't apply, not really sure why.

johannes