Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

Chris Wright
2009-12-23T15:17:22Z

* Anthony Liguori (anthony@codemonkey.ws) wrote:
> On 12/22/2009 06:02 PM, Chris Wright wrote:
>> * Anthony Liguori (anthony@codemonkey.ws) wrote:
>>> The
>>> virtio-net setup probably made extensive use of pinning and other tricks
>>> to make things faster than a normal user would see them. It ends up
>>> creating a perfect combination of batching which is pretty much just
>>> cooking the mitigation schemes to do extremely well for one benchmark.
>>
>> Just pinning, the rest is stock virtio features like mergeable rx buffers,
>> GRO, GSO (tx mitigation is actually disabled).
>
> Technically, tx mitigation isn't disabled. The heuristic is changed
> such that instead of relying on a fixed timer, tx notification is
> disabled until you can switch to another thread and process packets.
>
> The effect is that depending on time slice length and system load, you
> adaptively enable tx mitigation. It's heavily dependent on the
> particulars of the system and the overall load.
>
> For instance, this mitigation scheme looks great at high throughputs but
> looks very bad at mid-to-low throughputs compared to timer based
> mitigation (at least, when comparing CPU cost).

Yep, you're right.

thanks,
-chris