netdev - Re: [RFC PATCH v2 bpf-next 00/15] xdp

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Message-ID: <25ade2e7-a8fe-2adb-8d4c-6cc6add21267@gmail.com>
Date:   Mon, 21 Oct 2019 20:47:17 +0900
From:   Toshiaki Makita <toshiaki.makita1@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        William Tu <u9012063@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Pravin B Shelar <pshelar@....org>,
        Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Stanislav Fomichev <sdf@...ichev.me>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>
Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

On 2019/10/21 20:23, Björn Töpel wrote:
> On Sat, 19 Oct 2019 at 00:31, Toshiaki Makita
> <toshiaki.makita1@...il.com> wrote:
>>
> [...]
>>
>> * About OVS AF_XDP netdev
>>
>> Recently OVS has added AF_XDP netdev type support. This also makes use
>> of XDP, but in some ways different from this patch set.
>>
>> - AF_XDP work originally started in order to bring BPF's flexibility to
>>    OVS, which enables us to upgrade datapath without updating kernel.
>>    AF_XDP solution uses userland datapath so it achieved its goal.
>>    xdp_flow will not replace OVS datapath completely, but offload it
>>    partially just for speed up.
>>
>> - OVS AF_XDP requires PMD for the best performance so consumes 100% CPU
>>    as well as using another core for softirq.
>>
> 
> Disclaimer; I haven't studied the OVS AF_XDP code, so this is about
> AF_XDP in general.
> 
> One of the nice things about AF_XDP is that it *doesn't* force a user
> to busy-poll (burn CPUs) like a regular userland pull-mode driver.
> Yes, you can do that if you're extremely latency sensitive, but for
> most users (and I think some OVS deployments might fit into this
> category) not pinning cores/interrupts and using poll() syscalls (need
> wakeup patch [1]) is the way to go. The scenario you're describing
> with ksoftirqd spinning on one core, and user application on another
> is not something I'd recommend, rather run your packet processing
> application on one core together with the softirq processing.

Thank you for the information.
I want to evaluate AF_XDP solution more appropriately.

William, please correct me if I'm saying something wrong here.
Or guide me if more appropriate configuration to achieve best performance is possible.

> 
> Björn
> [1] https://lore.kernel.org/bpf/1565767643-4908-1-git-send-email-magnus.karlsson@intel.com/#t

Toshiaki Makita