netdev - Re: Kernel 4.13.0-rc4-next-20170811 - IP Routing / Forwarding performance vs Core/RSS number / HT on

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Message-ID: <1502728387.4936.26.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 14 Aug 2017 09:33:07 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Paweł Staszewski <pstaszewski@...are.pl>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: Kernel 4.13.0-rc4-next-20170811 - IP Routing / Forwarding
 performance vs Core/RSS number / HT on

On Mon, 2017-08-14 at 18:19 +0200, Jesper Dangaard Brouer wrote:

> The output (extracted below) didn't show who called 'do_raw_spin_lock',
> BUT it showed another interesting thing.  The kernel code
> __dev_queue_xmit() in might create route dst-cache problem for itself(?),
> as it will first call skb_dst_force() and then skb_dst_drop() when the
> packet is transmitted on a VLAN.
> 
>  static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv)
>  {
>  [...]
> 	/* If device/qdisc don't need skb->dst, release it right now while
> 	 * its hot in this cpu cache.
> 	 */
> 	if (dev->priv_flags & IFF_XMIT_DST_RELEASE)
> 		skb_dst_drop(skb);
> 	else
> 		skb_dst_force(skb);

This is explained in this commit changelog.

https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=93f154b594fe47e4a7e5358b309add449a046cd3