netdev - RE: [PATCH net-next] iwlwifi: dont pull too much payload in skb head

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Date:	Fri, 18 May 2012 14:59:04 +0000
From:	"Berg, Johannes" <johannes.berg@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	netdev <netdev@...r.kernel.org>,
	"Guy, Wey-Yi W" <wey-yi.w.guy@...el.com>
Subject: RE: [PATCH net-next] iwlwifi: dont pull too much payload in skb head

> Since merge window is now pretty close, I would prefer David applies this
> directly in net-next, if you dont mind, as this patch is more a core network issue
> than an iwlwifi one.
> 
> Thanks !

Sure, good with me, I don't think we have colliding patches.

Reviewed-by: Johannes Berg <johannes.berg@...el.com>

> As iwlwifi use fat skbs, it should not pull too much data in skb->head, and
> particularly no tcp data payload, or splice() is slower, and TCP coalescing is
> disabled. Copying payload to userland also involves at least two copies (part
> from header, part from fragment)
> 
> Each layer will pull its header from the fragment as needed.
> 
> (on 64bit arches, skb_tailroom(skb) at this point is 192 bytes)
> 
> With this patch applied, I have a major reduction of collapsed/pruned TCP
> packets, a nice increase of TCPRcvCoalesce counter, and overall better Internet
> User experience.
> 
> Small packets are still using a fragless skb, so that page can be reused by the
> driver.

We may want to move this code into mac80211 later though since it also has an if (pull in everything, even reallocating if necessary, if it's a management frame), but that can wait, I think we're the only driver using paged RX.

johannes

PS: sorry about the footer -- unfortunately I haven't managed to convince IT to remove it on my @intel address
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