From: Jesper Dangaard Brouer <brouer@redhat.com>
To: "Björn Töpel" <bjorn.topel@gmail.com>
Cc: Netdev <netdev@vger.kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
bpf <bpf@vger.kernel.org>,
"Magnus Karlsson" <magnus.karlsson@gmail.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>,
"Jonathan Lemon" <jonathan.lemon@gmail.com>,
"Edward Cree" <ecree@solarflare.com>,
"Toke Høiland-Jørgensen" <thoiland@redhat.com>,
"Andrii Nakryiko" <andrii.nakryiko@gmail.com>,
brouer@redhat.com
Subject: Re: [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher
Date: Mon, 9 Dec 2019 20:50:10 +0100 [thread overview]
Message-ID: <20191209205010.153a9060@carbon> (raw)
In-Reply-To: <CAJ+HfNhikfpdAi3wC_s72Z-S8iMYUe7=hOBP_jNFQz++jrPgzg@mail.gmail.com>
On Mon, 9 Dec 2019 18:45:12 +0100
Björn Töpel <bjorn.topel@gmail.com> wrote:
> On Mon, 9 Dec 2019 at 18:00, Jesper Dangaard Brouer <brouer@redhat.com> wrote:
> >
> > On Mon, 9 Dec 2019 14:55:16 +0100
> > Björn Töpel <bjorn.topel@gmail.com> wrote:
> >
> > > Performance
> > > ===========
> > >
> > > The tests were performed using the xdp_rxq_info sample program with
> > > the following command-line:
> > >
> > > 1. XDP_DRV:
> > > # xdp_rxq_info --dev eth0 --action XDP_DROP
> > > 2. XDP_SKB:
> > > # xdp_rxq_info --dev eth0 -S --action XDP_DROP
> > > 3. xdp-perf, from selftests/bpf:
> > > # test_progs -v -t xdp_perf
> > >
> > >
> > > Run with mitigations=auto
> > > -------------------------
> > >
> > > Baseline:
> > > 1. 22.0 Mpps
> > > 2. 3.8 Mpps
> > > 3. 15 ns
> > >
> > > Dispatcher:
> > > 1. 29.4 Mpps (+34%)
> > > 2. 4.0 Mpps (+5%)
> > > 3. 5 ns (+66%)
> >
> > Thanks for providing these extra measurement points. This is good
> > work. I just want to remind people that when working at these high
> > speeds, it is easy to get amazed by a +34% improvement, but we have to
> > be careful to understand that this is saving approx 10 ns time or
> > cycles.
> >
> > In reality cycles or time saved in #2 (3.8 Mpps -> 4.0 Mpps) is larger
> > (1/3.8-1/4)*1000 = 13.15 ns. Than #1 (22.0 Mpps -> 29.4 Mpps)
> > (1/22-1/29.4)*1000 = 11.44 ns. Test #3 keeps us honest 15 ns -> 5 ns =
> > 10 ns. The 10 ns improvement is a big deal in XDP context, and also
> > correspond to my own experience with retpoline (approx 12 ns overhead).
> >
>
> Ok, good! :-)
>
> > To Bjørn, I would appreciate more digits on your Mpps numbers, so I get
> > more accuracy on my checks-and-balances I described above. I suspect
> > the 3.8 Mpps -> 4.0 Mpps will be closer to the other numbers when we
> > get more accuracy.
> >
>
> Ok! Let me re-run them.
Well, I don't think you should waste your time re-running these...
It clearly shows a significant improvement. I'm just complaining that
I didn't have enough digits to do accurate checks-and-balances, they
are close enough that I believe them.
> If you have some spare cycles, yt would be
> great if you could try it out as well on your Mellanox setup.
I'll add it to my TODO list... but no promises.
> Historically you've always been able to get more stable numbers than
> I. :-)
>
> >
> > > Dispatcher (full; walk all entries, and fallback):
> > > 1. 20.4 Mpps (-7%)
> > > 2. 3.8 Mpps
> > > 3. 18 ns (-20%)
> > >
> > > Run with mitigations=off
> > > ------------------------
> > >
> > > Baseline:
> > > 1. 29.6 Mpps
> > > 2. 4.1 Mpps
> > > 3. 5 ns
> > >
> > > Dispatcher:
> > > 1. 30.7 Mpps (+4%)
> > > 2. 4.1 Mpps
> > > 3. 5 ns
> >
> > While +4% sounds good, but could be measurement noise ;-)
> >
> > (1/29.6-1/30.7)*1000 = 1.21 ns
> >
> > As both #3 says 5 ns.
> >
>
> True. Maybe that simply hints that we shouldn't use the dispatcher here?
No. I actually think it is worth exposing this code as much as
possible. And if it really is 1.2 ns improvement, then I'll gladly take
that as well ;-)
I think this is awesome work! -- thanks for doing this!!!
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2019-12-09 19:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-09 13:55 [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 1/6] bpf: move trampoline JIT image allocation to a function Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 2/6] bpf: introduce BPF dispatcher Björn Töpel
2019-12-10 5:50 ` Alexei Starovoitov
2019-12-10 5:54 ` Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 3/6] bpf, xdp: start using the BPF dispatcher for XDP Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 4/6] bpf: start using the BPF dispatcher in BPF_TEST_RUN Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 5/6] selftests: bpf: add xdp_perf test Björn Töpel
2019-12-10 11:05 ` Jesper Dangaard Brouer
2019-12-10 11:56 ` Björn Töpel
2019-12-09 13:55 ` [PATCH bpf-next v3 6/6] bpf, x86: align dispatcher branch targets to 16B Björn Töpel
2019-12-09 15:00 ` [PATCH bpf-next v3 0/6] Introduce the BPF dispatcher Toke Høiland-Jørgensen
2019-12-09 17:42 ` Björn Töpel
2019-12-11 12:38 ` Björn Töpel
2019-12-11 13:17 ` Toke Høiland-Jørgensen
2019-12-09 17:00 ` Jesper Dangaard Brouer
2019-12-09 17:45 ` Björn Töpel
2019-12-09 19:50 ` Jesper Dangaard Brouer [this message]
2019-12-10 19:28 ` Samudrala, Sridhar
2019-12-10 20:04 ` Björn Töpel
2019-12-10 19:59 ` Björn Töpel
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