netdev - Re: [PATCH net-next] net: sock_rps_record

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Date:   Thu, 8 Dec 2016 09:49:23 -0800
From:   Tom Herbert <tom@...bertland.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Paolo Abeni <pabeni@...hat.com>,
        David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] net: sock_rps_record_flow() is for connected sockets

On Tue, Dec 6, 2016 at 10:47 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2016-12-06 at 19:32 -0800, Eric Dumazet wrote:
>> A follow up patch will provide a static_key (Jump Label) since most
>> hosts do not even use RFS.
>
> Speaking of static_key, it appears we now have GRO on UDP, and this
> consumes a considerable amount of cpu cycles.
>
> Turning off GRO allows me to get +20 % more packets on my single UDP
> socket. (1.2 Mpps instead of 1.0 Mpps)
>
> Surely udp_gro_receive() should be bypassed if no UDP socket has
> registered a udp_sk(sk)->gro_receive handler
>
> And/or delay the inet_add_offload(&udpv{4|6}_offload, IPPROTO_UDP); to
> the first UDP sockets setting udp_sk(sk)->gro_receive handler,
> ie udp_encap_enable() and udpv6_encap_enable()
>
Of course that would only help on systems where no one enable encaps,
ie. looks good in the the simple benchmarks but in real life if just
one socket enables encap everyone else takes the hit. Alternatively,
maybe we could do early demux when we do the lookup in GRO to
eliminate the extra lookup?

Tom

>
> :(
>
>
>