netdev - Re: [Intel-wired-lan] i40e X722 RSS problem with NAT-Traversal IPsec packets

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Message-ID: <20190503205935.bg45rsso5jjj3gnx@csclub.uwaterloo.ca>
Date:   Fri, 3 May 2019 16:59:35 -0400
From:   lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [Intel-wired-lan] i40e X722 RSS problem with NAT-Traversal IPsec
 packets

On Fri, May 03, 2019 at 10:19:47AM -0700, Alexander Duyck wrote:
> The TCP flow could be bypassing RSS and may be using ATR to decide
> where the Rx packets are processed. Now that I think about it there is
> a possibility that ATR could be interfering with the queue selection.
> You might try disabling it by running:
>     ethtool --set-priv-flags <iface> flow-director-atr off

Hmm, I thought I had killed ATR (I certainly meant to), but it appears
I had not.  I will experiment to see if that makes a difference.

> The problem is RSS can be bypassed for queue selection by things like
> ATR which I called out above. One possibility is that if the
> encryption you were using was leaving the skb->encapsulation flag set,
> and the NIC might have misidentified the packets as something it could
> parse and set up a bunch of rules that were rerouting incoming traffic
> based on outgoing traffic. Disabling the feature should switch off
> that behavior if that is in fact the case.
> 
> You are probably fine using 40 queues. That isn't an even power of two
> so it would actually improve the entropy a bit since the lower bits
> don't have a many:1 mapping to queues.

I will let you know Monday how my tests go with atr off.  I really
thought that was off already since it was supposed to be.  We always
try to turn that off because it does not work well.

-- 
Len Sorensen