Intel 82574L (em)

[Sepherosa Ziehau]

On Sat, Jan 31, 2015 at 5:11 AM, Sean Bruno <sbruno at ignoranthack.me> wrote:
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> http://www.intel.com/content/dam/doc/datasheet/82574l-gbe-controller-datasheet.pdf
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> According to 7.1.11, this device does indeed have 2 queues for stuff and
> or things.  So, basic RSS would be possible in something like an Atom box.
>
> I note that the em(4) driver intentionally disables this on
> initialization.  I'm up for some science on my new shiny, soon to be
> router box. Any reason not to default to 1 queue and allow loader.conf
> to raise it to 2?

You could actually enable 2 RX rings w/o MSI-X on 82574; you still get
the benefit of hardware calculated RSS hash at least.  And as far as I
have tested, 2 RX rings work for 82574L, but 2 TX rings don't work
(gave me TX watchdog timeout).  And you could also use 2 RX rings on
82571/82572/82573 and i217/i218; 2 TX rings work on 82571 at least
(you need to setup TX context for each TX descriptor though).

Best Regards,
sephe