netdev - Re: ixgbe tuning reset when XDP is setup

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Date:   Fri, 15 Dec 2017 08:51:11 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     David Miller <davem@...emloft.net>, eric@...it.org,
        Netdev <netdev@...r.kernel.org>, xdp-newbies@...r.kernel.org,
        pmanev@...mus-networks.com,
        Emil Tantilov <emil.s.tantilov@...el.com>
Subject: Re: ixgbe tuning reset when XDP is setup

On Fri, Dec 15, 2017 at 8:03 AM, John Fastabend
<john.fastabend@...il.com> wrote:
> On 12/15/2017 07:53 AM, David Miller wrote:
>> From: Eric Leblond <eric@...it.org>
>> Date: Fri, 15 Dec 2017 11:24:46 +0100
>>
>>> Hello,
>>>
>>> When using an ixgbe card with Suricata we are using the following
>>> commands to get a symmetric hash on RSS load balancing:
>>>
>>> ./set_irq_affinity 0-15 eth3
>>> ethtool -X eth3 hkey 6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A:6D:5A equal 16
>>> ethtool -x eth3
>>> ethtool -n eth3
>>>
>>> Then we start Suricata.
>>>
>>> In my current experiment on XDP, I have Suricata that inject the eBPF
>>> program when starting. The consequence of that when using an ixgbe card
>>> is that the load balancing get reset and all interrupts are reaching
>>> the first core.
>>
>> This definitely should _not_ be a side effect of enabling XDP on a device.
>>
>
> Agreed, CC Emil and Alex we should restore these settings after the
> reconfiguration done to support a queue per core.
>
> .John

So the interrupt configuration has to get reset since we have to
assign 2 Tx queues for every Rx queue instead of the 1-1 that was
previously there. That is a natural consequence of rearranging the
queues as currently happens. The issue is the q_vectors themselves
have to be reallocated. The only way to not make that happen would be
to pre-allocate the Tx queues for XDP always.

Also just to be clear we are talking about the interrupts being reset,
not the RSS key right? I just want to make sure that is what we are
talking about.

Thanks.

- Alex