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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: William Tu <u9012063@gmail.com>,
	Toshiaki Makita <toshiaki.makita1@gmail.com>
Cc: David Miller <davem@davemloft.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	Jiri Pirko <jiri@resnulli.us>,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	Jozsef Kadlecsik <kadlec@netfilter.org>,
	Florian Westphal <fw@strlen.de>, pravin shelar <pshelar@ovn.org>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, Stanislav Fomichev <sdf@fomichev.me>
Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP
Date: Fri, 15 Nov 2019 14:16:01 +0100	[thread overview]
Message-ID: <877e41mga6.fsf@toke.dk> (raw)
In-Reply-To: <CALDO+SbqcoiwJn3jskpPTjdJyK5932r0cEzs=1R6p=CWgERLuw@mail.gmail.com>

William Tu <u9012063@gmail.com> writes:

> On Thu, Nov 14, 2019 at 2:06 AM Toshiaki Makita
> <toshiaki.makita1@gmail.com> wrote:
>>
>> On 2019/11/13 2:50, William Tu wrote:
>> > On Wed, Oct 30, 2019 at 5:32 PM Toshiaki Makita
>> > <toshiaki.makita1@gmail.com> wrote:
>> >>
>> >> On 2019/10/28 4:17, David Miller wrote:
>> >>> From: Toke Høiland-Jørgensen <toke@redhat.com>
>> >>> Date: Sun, 27 Oct 2019 16:24:24 +0100
>> >>>
>> >>>> The results in the paper also shows somewhat disappointing performance
>> >>>> for the eBPF implementation, but that is not too surprising given that
>> >>>> it's implemented as a TC eBPF hook, not an XDP program. I seem to recall
>> >>>> that this was also one of the things puzzling to me back when this was
>> >>>> presented...
>> >>>
>> >>> Also, no attempt was made to dyanamically optimize the data structures
>> >>> and code generated in response to features actually used.
>> >>>
>> >>> That's the big error.
>> >>>
>> >>> The full OVS key is huge, OVS is really quite a monster.
>> >>>
>> >>> But people don't use the entire key, nor do they use the totality of
>> >>> the data paths.
>> >>>
>> >>> So just doing a 1-to-1 translation of the OVS datapath into BPF makes
>> >>> absolutely no sense whatsoever and it is guaranteed to have worse
>> >>> performance.
>> >
>> > 1-to-1 translation has nothing to do with performance.
>>
>> I think at least key size matters.
>> One big part of hot spots in xdp_flow bpf program is hash table lookup.
>> Especially hash calculation by jhash and key comparison are heavy.
>> The computational cost heavily depends on key size.
>>
>> If umh can determine some keys won't be used in some way (not sure if it's
>> practical though), umh can load an XDP program which uses less sized
>> key. Also it can remove unnecessary key parser routines.
>> If it's possible, the performance will increase.
>>
> Yes, that's a good point.
> In other meeting people also gave me this suggestions.
>
> Basically it's "on-demand flow key parsing using eBPF"
> The key parsing consists of multiple eBPF programs, and
> based on the existing rules, load the program and parse minimum
> necessary fields required by existing rules. This will definitely
> have better performance.

See the xdp-filter program[0] for a simple example of how to do this
with pre-compiled BPF programs. Basically, what it does is generate
different versions of the same program with different subsets of
functionality included (through ifdefs). The feature set of each program
is saved as a feature bitmap, and the loader will dynamically select
which program to load based on which features the user enables at
runtime.

The nice thing about this is that it doesn't require dynamic program
generation, and everything can be compiled ahead of time. The drawback
is that you'll end up with a combinatorial explosion of program variants
if you want full granularity in your feature selection.

-Toke

[0] https://github.com/xdp-project/xdp-tools/tree/master/xdp-filter


  reply	other threads:[~2019-11-15 13:16 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-18  4:07 Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 01/15] xdp_flow: Add skeleton of XDP based flow offload driver Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 02/15] xdp_flow: Add skeleton bpf program for XDP Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 03/15] bpf: Add API to get program from id Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 04/15] xdp: Export dev_check_xdp and dev_change_xdp Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 05/15] xdp_flow: Attach bpf prog to XDP in kernel after UMH loaded program Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 06/15] xdp_flow: Prepare flow tables in bpf Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 07/15] xdp_flow: Add flow entry insertion/deletion logic in UMH Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 08/15] xdp_flow: Add flow handling and basic actions in bpf prog Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 09/15] xdp_flow: Implement flow replacement/deletion logic in xdp_flow kmod Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 10/15] xdp_flow: Add netdev feature for enabling flow offload to XDP Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 11/15] xdp_flow: Implement redirect action Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 12/15] xdp_flow: Implement vlan_push action Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 13/15] bpf, selftest: Add test for xdp_flow Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 14/15] i40e: prefetch xdp->data before running XDP prog Toshiaki Makita
2019-10-18  4:07 ` [RFC PATCH v2 bpf-next 15/15] bpf, hashtab: Compare keys in long Toshiaki Makita
2019-10-18 15:22 ` [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP John Fastabend
2019-10-21  7:31   ` Toshiaki Makita
2019-10-22 16:54     ` John Fastabend
2019-10-22 17:45       ` Toke Høiland-Jørgensen
2019-10-24  4:27         ` John Fastabend
2019-10-24 10:13           ` Toke Høiland-Jørgensen
2019-10-27 13:19             ` Toshiaki Makita
2019-10-27 15:21               ` Toke Høiland-Jørgensen
2019-10-28  3:16                 ` David Ahern
2019-10-28  8:36                   ` Toke Høiland-Jørgensen
2019-10-28 10:08                     ` Jesper Dangaard Brouer
2019-10-28 19:07                       ` David Ahern
2019-10-28 19:05                     ` David Ahern
2019-10-31  0:18                 ` Toshiaki Makita
2019-10-31 12:12                   ` Toke Høiland-Jørgensen
2019-11-11  7:32                     ` Toshiaki Makita
2019-11-12 16:53                       ` Toke Høiland-Jørgensen
2019-11-14 10:11                         ` Toshiaki Makita
2019-11-14 12:41                           ` Toke Høiland-Jørgensen
2019-11-18  6:41                             ` Toshiaki Makita
2019-11-18 10:20                               ` Toke Høiland-Jørgensen
2019-11-22  5:42                                 ` Toshiaki Makita
2019-11-22 11:54                                   ` Toke Høiland-Jørgensen
2019-11-25 10:18                                     ` Toshiaki Makita
2019-11-25 13:03                                       ` Toke Høiland-Jørgensen
2019-11-18 10:28                               ` Toke Høiland-Jørgensen
2019-10-27 13:13         ` Toshiaki Makita
2019-10-27 15:24           ` Toke Høiland-Jørgensen
2019-10-27 19:17             ` David Miller
2019-10-31  0:32               ` Toshiaki Makita
2019-11-12 17:50                 ` William Tu
2019-11-14 10:06                   ` Toshiaki Makita
2019-11-14 17:09                     ` William Tu
2019-11-15 13:16                       ` Toke Høiland-Jørgensen [this message]
2019-11-12 17:38             ` William Tu
2019-10-23 14:11       ` Jamal Hadi Salim
2019-10-24  4:38         ` John Fastabend
2019-10-24 17:05           ` Jamal Hadi Salim
2019-10-27 13:27         ` Toshiaki Makita
2019-10-27 13:06       ` Toshiaki Makita
2019-10-21 11:23 ` Björn Töpel
2019-10-21 11:47   ` Toshiaki Makita

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