netdev - Re: [PATCH bpf-next 11/11] samples/bpf: add -c/--copy -z/--zero-copy flags to xdpsock

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Date:   Thu, 30 Aug 2018 12:21:12 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        peter.waskiewicz.jr@...el.com,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        neerav.parikh@...el.com,
        MykytaI Iziumtsev <mykyta.iziumtsev@...aro.org>,
        Francois Ozog <francois.ozog@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Brian Brooks <brian.brooks@...aro.org>,
        William Tu <u9012063@...il.com>, pavel@...tnetmon.com,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [PATCH bpf-next 11/11] samples/bpf: add -c/--copy -z/--zero-copy
 flags to xdpsock

Den ons 29 aug. 2018 kl 14:44 skrev Jesper Dangaard Brouer <brouer@...hat.com>:
>
> On Tue, 28 Aug 2018 14:44:35 +0200
> Björn Töpel <bjorn.topel@...il.com> wrote:
>
> > From: Björn Töpel <bjorn.topel@...el.com>
> >
> > The -c/--copy -z/--zero-copy flags enforces either copy or zero-copy
> > mode.
>
> Nice, thanks for adding this.  It allows me to quickly test the
> difference between normal-copy vs zero-copy modes.
> (Kernel bpf-next without RETPOLINE).
>
> AF_XDP RX-drop:
>  Normal-copy mode: rx 13,070,318 pps - 76.5 ns
>  Zero-copy   mode: rx 26,132,328 pps - 38.3 ns
>
> Compare to XDP_DROP:  34,251,464 pps - 29.2 ns
>    XDP_DROP + read :  30,756,664 pps - 32.5 ns
>
> The normal-copy mode is surprisingly fast (and it works for every
> driver implemeting the regular XDP_REDIRECT action).  It is still
> faster to do in-kernel XDP_DROP than AF_XDP zero-copy mode dropping,
> which was expected given frames travel to a remote CPU before returned
> (don't think remote CPU reads payload?).  The gap in nanosec is
> actually quite small, thus I'm impressed by the SPSC-queue
> implementation working across these CPUs.
>
>
> AF_XDP layer2-fwd:
>  Normal-copy mode: rx  3,200,885   tx  3,200,892
>  Zero-copy   mode: rx 17,026,300   tx 17,026,269
>
> Compare to XDP_TX: rx 14,529,079   tx 14,529,850  - 68.82 ns
>      XDP_REDIRECT: rx 13,235,785   tx 13,235,784  - 75.55 ns
>
> The copy-mode is slow because it allocates SKBs internally (I do
> wonder if we could speed it up by using ndo_xdp_xmit + disable-BH).
> More intersting is that the zero-copy is faster than XDP_TX and
> XDP_REDIRECT. I think the speedup comes from avoiding some DMA mapping
> calls with ZC.
>
> Side-note: XDP_TX vs. REDIRECT: 75.55 - 68.82 = 6.73 ns.  The cost of
> going through the xdp_do_redirect_map core is actually quite small :-)
> (I have some micro optimizations that should help ~2ns).
>
>
> AF_XDP TX-only:
>  Normal-copy mode: tx  2,853,461 pps
>  Zero-copy   mode: tx 22,255,311 pps
>
> (There is not XDP mode that does TX to compare against)
>

Kudos for doing the in-depth benchmarking!


Thanks!
Björn

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer