RFC: use EM_LEGACY_IRQ in if_lem.c ?

[Adrian Chadd]

On 24 July 2012 13:20, Luigi Rizzo <rizzo at iet.unipi.it> wrote:
> if_lem.c ("lem", one of the e1000 drivers) has 2 possible interrupt modes:
> EM_LEGACY_IRQ uses the standard dispatch mechanism, whereas
> FAST_INTR has a custom handler that signals a taskqueue to do the job.
>
> I have no idea which actual hardware uses it (all of my Intel 1G
> cards use either "em" or "igb"), but "lem" is the driver used in
> qemu, and there the EM_LEGACY_IRQ gives approx 10% higher packet
> rates than the other.
>
> Any objections if i change the default to EM_LEGACY_IRQ ?

I suggest doing some digging to understand why. I bet we all know the
answer, but it would be nice to have it documented and investigated. I
bet em(4) isn't the only device that would benefit from this?

2c,


Adrian