From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:40290 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389582AbfEXJxO (ORCPT ); Fri, 24 May 2019 05:53:14 -0400 Date: Fri, 24 May 2019 11:53:01 +0200 From: Jesper Dangaard Brouer Subject: Re: [PATCH bpf-next 3/3] veth: Support bulk XDP_TX Message-ID: <20190524115301.7626ed44@carbon> In-Reply-To: References: <1558609008-2590-1-git-send-email-makita.toshiaki@lab.ntt.co.jp> <1558609008-2590-4-git-send-email-makita.toshiaki@lab.ntt.co.jp> <87zhnd1kg9.fsf@toke.dk> <599302b2-96d2-b571-01ee-f4914acaf765@lab.ntt.co.jp> <20190523152927.14bf7ed1@carbon> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: xdp-newbies-owner@vger.kernel.org List-ID: To: Toshiaki Makita Cc: Toshiaki Makita , Toke =?UTF-8?B?SMO4?= =?UTF-8?B?aWxhbmQtSsO4cmdlbnNlbg==?= , Alexei Starovoitov , Daniel Borkmann , "David S. Miller" , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , netdev@vger.kernel.org, xdp-newbies@vger.kernel.org, bpf@vger.kernel.org, brouer@redhat.com On Thu, 23 May 2019 22:51:34 +0900 Toshiaki Makita wrote: > On 19/05/23 (木) 22:29:27, Jesper Dangaard Brouer wrote: > > On Thu, 23 May 2019 20:35:50 +0900 > > Toshiaki Makita wrote: > > > >> On 2019/05/23 20:25, Toke Høiland-Jørgensen wrote: > >>> Toshiaki Makita 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 > >>>> --- > >>>> 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. > >> > > > > I think the general per-cpu TX bulk queue is overkill. There is a loop > > over packets in veth_xdp_rcv(struct veth_rq *rq, budget, *status), and > > the caller veth_poll() will call veth_xdp_flush(rq->dev). > > > > Why can't you store this "temp" bulk array in struct veth_rq ? > > Of course I can. But I thought tun has the same problem and we can > decrease memory footprint by sharing the same storage between devices. > Or if other devices want to reduce queues so that we can use XDP on > many-cpu servers and introduce locks, we can use this storage for > that case as well. > > Still do you prefer veth-specific solution? Yes. Another reason is that with this shared/general per-cpu TX bulk queue, I can easily see bugs resulting in xdp_frames getting transmitted on a completely other NIC, which will be hard to debug for people. > > > > You could even alloc/create it on the stack of veth_poll() and send > > it along via a pointer to veth_xdp_rcv). IHMO it would be cleaner code wise to place the "temp" bulk array in struct veth_rq. But if you worry about performance and want a hot cacheline for this, then you could just use the call-stack for veth_poll(), as I described. It should not be too ugly code wise to do this I think. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer