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SubjectRe: Regression: Approximate 34% performance hit in receive throughput over ixgbe seen due to build_skb patch
On Tue, May 22, 2018 at 12:29 PM, William Kucharski
<william.kucharski@oracle.com> wrote:
>
>
>> On May 22, 2018, at 12:23 PM, Alexander Duyck <alexander.duyck@gmail.com> wrote:
>>
>> 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
> 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
> 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
>

I would think with modification of interrupt delay you could probably
do much better if my assumption is correct and the issue is us sitting
on packets for too long so we overrun the socket buffer and start
dropping packets or stalling the Tx.

Thanks.

- Alex

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