netdev - Re: [PATCH bpf-next 3/3] veth: Support bulk XDP

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Message-ID: <87sgt51i0e.fsf@toke.dk>
Date:   Thu, 23 May 2019 14:18:25 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>
Cc:     netdev@...r.kernel.org, xdp-newbies@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next 3/3] veth: Support bulk XDP_TX

Toshiaki Makita <makita.toshiaki@....ntt.co.jp> writes:

> On 2019/05/23 20:25, Toke Høiland-Jørgensen wrote:
>> Toshiaki Makita <makita.toshiaki@....ntt.co.jp> writes:
>> 
>>> This improves XDP_TX performance by about 8%.
>>>
>>> Here are single core XDP_TX test results. CPU consumptions are taken
>>> from "perf report --no-child".
>>>
>>> - Before:
>>>
>>>   7.26 Mpps
>>>
>>>   _raw_spin_lock  7.83%
>>>   veth_xdp_xmit  12.23%
>>>
>>> - After:
>>>
>>>   7.84 Mpps
>>>
>>>   _raw_spin_lock  1.17%
>>>   veth_xdp_xmit   6.45%
>>>
>>> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
>>> ---
>>>  drivers/net/veth.c | 26 +++++++++++++++++++++++++-
>>>  1 file changed, 25 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
>>> index 52110e5..4edc75f 100644
>>> --- a/drivers/net/veth.c
>>> +++ b/drivers/net/veth.c
>>> @@ -442,6 +442,23 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
>>>  	return ret;
>>>  }
>>>  
>>> +static void veth_xdp_flush_bq(struct net_device *dev)
>>> +{
>>> +	struct xdp_tx_bulk_queue *bq = this_cpu_ptr(&xdp_tx_bq);
>>> +	int sent, i, err = 0;
>>> +
>>> +	sent = veth_xdp_xmit(dev, bq->count, bq->q, 0);
>> 
>> Wait, veth_xdp_xmit() is just putting frames on a pointer ring. So
>> you're introducing an additional per-cpu bulk queue, only to avoid lock
>> contention around the existing pointer ring. But the pointer ring is
>> per-rq, so if you have lock contention, this means you must have
>> multiple CPUs servicing the same rq, no?
>
> Yes, it's possible. Not recommended though.
>
>> So why not just fix that instead?
>
> The queues are shared with packets from stack sent from peer. That's
> because I needed the lock. I have tried to separate the queues, one for
> redirect and one for stack, but receiver side got too complicated and it
> ended up with worse performance.

I meant fix it with configuration. Now many receive queues are you
running on the veth device in your benchmarks, and how have you
configured the RPS?

-Toke