linux-kernel - Re: [PATCH net-next v3] tun: support NAPI for packets received from batched XDP buffs

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Message-ID: <CAHJXk3Yth1Q0BTcza8ndpECL3fGjeTYyv3wCAasdog0o6rd2hA@mail.gmail.com>
Date:   Tue, 1 Mar 2022 09:58:39 +0800
From:   Harold Huang <baymaxhuang@...il.com>
To:     stephen@...workplumber.org
Cc:     Jason Wang <jasowang@...hat.com>, netdev <netdev@...r.kernel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v3] tun: support NAPI for packets received from
 batched XDP buffs

On Tue, Mar 1, 2022 at 1:15 AM Stephen Hemminger
<stephen@...workplumber.org> wrote:
>
> On Mon, 28 Feb 2022 15:46:56 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
> > On Mon, Feb 28, 2022 at 11:38 AM Harold Huang <baymaxhuang@...il.com> wrote:
> > >
> > > In tun, NAPI is supported and we can also use NAPI in the path of
> > > batched XDP buffs to accelerate packet processing. What is more, after
> > > we use NAPI, GRO is also supported. The iperf shows that the throughput of
> > > single stream could be improved from 4.5Gbps to 9.2Gbps. Additionally, 9.2
> > > Gbps nearly reachs the line speed of the phy nic and there is still about
> > > 15% idle cpu core remaining on the vhost thread.
> > >
> > > Test topology:
> > > [iperf server]<--->tap<--->dpdk testpmd<--->phy nic<--->[iperf client]
> > >
> > > Iperf stream:
> > > iperf3 -c 10.0.0.2  -i 1 -t 10
> > >
> > > Before:
> > > ...
> > > [  5]   5.00-6.00   sec   558 MBytes  4.68 Gbits/sec    0   1.50 MBytes
> > > [  5]   6.00-7.00   sec   556 MBytes  4.67 Gbits/sec    1   1.35 MBytes
> > > [  5]   7.00-8.00   sec   556 MBytes  4.67 Gbits/sec    2   1.18 MBytes
> > > [  5]   8.00-9.00   sec   559 MBytes  4.69 Gbits/sec    0   1.48 MBytes
> > > [  5]   9.00-10.00  sec   556 MBytes  4.67 Gbits/sec    1   1.33 MBytes
> > > - - - - - - - - - - - - - - - - - - - - - - - - -
> > > [ ID] Interval           Transfer     Bitrate         Retr
> > > [  5]   0.00-10.00  sec  5.39 GBytes  4.63 Gbits/sec   72          sender
> > > [  5]   0.00-10.04  sec  5.39 GBytes  4.61 Gbits/sec               receiver
> > >
> > > After:
> > > ...
> > > [  5]   5.00-6.00   sec  1.07 GBytes  9.19 Gbits/sec    0   1.55 MBytes
> > > [  5]   6.00-7.00   sec  1.08 GBytes  9.30 Gbits/sec    0   1.63 MBytes
> > > [  5]   7.00-8.00   sec  1.08 GBytes  9.25 Gbits/sec    0   1.72 MBytes
> > > [  5]   8.00-9.00   sec  1.08 GBytes  9.25 Gbits/sec   77   1.31 MBytes
> > > [  5]   9.00-10.00  sec  1.08 GBytes  9.24 Gbits/sec    0   1.48 MBytes
> > > - - - - - - - - - - - - - - - - - - - - - - - - -
> > > [ ID] Interval           Transfer     Bitrate         Retr
> > > [  5]   0.00-10.00  sec  10.8 GBytes  9.28 Gbits/sec  166          sender
> > > [  5]   0.00-10.04  sec  10.8 GBytes  9.24 Gbits/sec               receiver
> > >
> > > Reported-at: https://lore.kernel.org/all/CACGkMEvTLG0Ayg+TtbN4q4pPW-ycgCCs3sC3-TF8cuRTf7Pp1A@mail.gmail.com
> > > Signed-off-by: Harold Huang <baymaxhuang@...il.com>
> >
> > Acked-by: Jason Wang <jasowang@...hat.com>
>
> Would this help when using sendmmsg and recvmmsg on the TAP device?
> Asking because interested in speeding up another use of TAP device, and wondering
> if this would help.

As Jason said, sendmmsg()/recvmsg() could not be used on tuntap. But I
think another choice is to use writev/readv directly on the ttunap fd,
which will call tun_get_user to send msg and NAPI has also been
supported.