82574 DMA Burst Mode Enablement

82574 DMA Burst Mode Enablement

[Denis Radovanovic]

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Hi,

We are currently testing small packet performance on 82574, comparing it to 82571. Initial pktgen measurements have shown a significant difference in performance that is the most visible when running bidirectional traffic with 256 byte packets.

Looking at the e1000e driver, we noticed that flag FLAG2_DMA_BURST is enabled for 82571 and 82572 but it is not enabled for 82574. After enabling the flag, the 82574 performance significantly improved, approaching the one on 82571.

Is there a reason that this flag is not enabled for 82574?

Thank you,
Denis Radovanovic

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Re: 82574 DMA Burst Mode Enablement

[Jesse Brandeburg]

On Wed, 28 Sep 2011 11:39:54 -0700
Denis Radovanovic <Denis.Radovanovic@riverbed.com> wrote:
> We are currently testing small packet performance on 82574, comparing
> it to 82571. Initial pktgen measurements have shown a significant
> difference in performance that is the most visible when running
> bidirectional traffic with 256 byte packets.
> 
> Looking at the e1000e driver, we noticed that flag FLAG2_DMA_BURST is
> enabled for 82571 and 82572 but it is not enabled for 82574. After
> enabling the flag, the 82574 performance significantly improved,
> approaching the one on 82571.

At the time the feature was implemented we didn't have the bandwidth to
validate it on other parts besides 82571/2

As it stands, yes you can enable it, but there will likely be some bugs
that you will run into that we already know about but don't fully have
fixed in the code.  The bugs might result in tx hangs or other issues.
I do agree that there are significant performance gains to be had via
this feature, if the bugs can all be worked out.

if this is a feature that you would really like implemented please use
your Intel Field Agent or TME contacts  in order to document your requirement 
so we can consider it for future releases.

Thanks,
  Jesse

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