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Subject: Re: Regression: Approximate 34% performance hit in receive throughput
 over ixgbe seen due to build_skb patch
From:   William Kucharski <william.kucharski@oracle.com>
In-Reply-To: <CAKgT0Ud2qriAkWcs56WEkw2vhYzBbWvzZOoY24ndsqPKaWn=Sg@mail.gmail.com>
Date:   Tue, 22 May 2018 13:29:53 -0600
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Netdev <netdev@vger.kernel.org>,
        intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
        Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
        "Duyck, Alexander H" <alexander.h.duyck@intel.com>
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 <CAKgT0Ud2qriAkWcs56WEkw2vhYzBbWvzZOoY24ndsqPKaWn=Sg@mail.gmail.com>
To:     Alexander Duyck <alexander.duyck@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On May 22, 2018, at 12:23 PM, Alexander Duyck =
<alexander.duyck@gmail.com> wrote:
>=20
> 3. There should be a private flag that can be updated via "ethtool
> --set-priv-flags" called "legacy-rx" that you can enable that will
> roll back to the original that did the copy-break type approach for
> small packets and the headers of the frame.

With legacy-rx enabled, most of the regression goes away, but it's still =
present
as compared to the code without the patch; the regression then drops to =
about 6%:

# ethtool --show-priv-flags eno1
Private flags for eno1:
legacy-rx: on

Socket  Message  Elapsed      Messages               =20
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

 65536      64   60.00     35934709      0     306.64
 65536           60.00     33791739            288.35

Socket  Message  Elapsed      Messages               =20
Size    Size     Time         Okay Errors   Throughput
bytes   bytes    secs            #      #   10^6bits/sec

 65536      64   60.00     39254351      0     334.97
 65536           60.00     36761069            313.69

Is this variance to be expected, or do you think modification of the
interrupt delay would achieve better results?


    William Kucharski