netdev - Re: [PATCH net-next] net: use jump label patching for ingress qdisc in __netif_receive_skb

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Message-Id: <20150413.133505.56878477510338170.davem@davemloft.net>
Date:	Mon, 13 Apr 2015 13:35:05 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	daniel@...earbox.net
Cc:	jhs@...atatu.com, ast@...mgrid.com, edumazet@...gle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: use jump label patching for ingress
 qdisc in __netif_receive_skb_core

From: Daniel Borkmann <daniel@...earbox.net>
Date: Fri, 10 Apr 2015 23:07:54 +0200

> Even if we make use of classifier and actions from the egress
> path, we're going into handle_ing() executing additional code
> on a per-packet cost for ingress qdisc, just to realize that
> nothing is attached on ingress.
> 
> Instead, this can just be blinded out as a no-op entirely with
> the use of a static key. On input fast-path, we already make
> use of static keys in various places, e.g. skb time stamping,
> in RPS, etc. It makes sense to not waste time when we're assured
> that no ingress qdisc is attached anywhere.
> 
> Enabling/disabling of that code path is being done via two
> helpers, namely net_{inc,dec}_ingress_queue(), that are being
> invoked under RTNL mutex when a ingress qdisc is being either
> initialized or destructed.
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>

This seems reasonable.  If it is shown to slow things down or
whatever, we can revert it.

Applied, thanks Daniel.
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