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

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Message-Id: <20191027.121727.1776345635168200501.davem@davemloft.net>
Date:   Sun, 27 Oct 2019 12:17:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     toke@...hat.com
Cc:     toshiaki.makita1@...il.com, john.fastabend@...il.com,
        ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, jakub.kicinski@...ronome.com,
        hawk@...nel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        jiri@...nulli.us, pablo@...filter.org, kadlec@...filter.org,
        fw@...len.de, pshelar@....org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, u9012063@...il.com, sdf@...ichev.me
Subject: Re: [RFC PATCH v2 bpf-next 00/15] xdp_flow: Flow offload to XDP

From: Toke Høiland-Jørgensen <toke@...hat.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.