netdev - Re: [iovisor-dev] README: [PATCH RFC 11/11] net/mlx5e: XDP TX xmit more

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Message-ID: <20160913184738.706e2d91@redhat.com>
Date:   Tue, 13 Sep 2016 18:47:38 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Edward Cree <ecree@...arflare.com>,
        Saeed Mahameed <saeedm@....mellanox.co.il>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tom Herbert <tom@...bertland.com>,
        iovisor-dev <iovisor-dev@...ts.iovisor.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Rana Shahout <rana.shahot@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>, brouer@...hat.com
Subject: Re: [iovisor-dev] README: [PATCH RFC 11/11] net/mlx5e: XDP TX xmit
 more

On Tue, 13 Sep 2016 08:58:30 -0700
Eric Dumazet <eric.dumazet@...il.com> wrote:

> We also care about icache pressure, and GRO/TSO already provides
> bundling where it is applicable, without adding insane complexity in
> the stacks.

Sorry, I cannot resist. The GRO code is really bad regarding icache
pressure/usage, due to how everything is function pointers calling
function pointers, even if the general case is calling the function
defined just next to it in the same C-file (which usually cause
inlining).  I can easily get 10% more performance for UDP use-cases by
simply disabling the GRO code, and I measure a significant drop in
icache-misses.

Edward's solution should lower icache pressure.

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