Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

From: Anthony Liguori
Date: Wed Dec 23 2009 - 10:12:37 EST

On 12/22/2009 06:02 PM, Chris Wright wrote:
* Anthony Liguori (anthony@xxxxxxxxxxxxx) wrote:
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).


Anthony Liguori
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at