Re: [PATCH v5] virtio-net: clarify coalescing parameters settings

Halil Pasic
2024-06-07T20:02:54Z

On Tue, 28 May 2024 12:47:02 +0800
Heng Qi <hengqi@linux.alibaba.com> wrote:

> The device can set any initial coalescing parameters (0 or non-zero)
> for the receive/send queue before the setting command is executed,
> not just 0, enhancing device performance even without DIM enabled.
>
> So we need to clarify descriptions that don't fit the behavior.

Sorry I'm late to the party -- again! Just for my understanding: how/why
is this a clarification and not just a (basically incompatible) change?

I mean if I read this correctly, before the driver had the guaranty
that if the parameters are not set by the driver, negotiating the
feature does not introduce any coalescing. After this in theory
the device could just pick some max value and potentially introduce
maximal latency in certain scenarios.

I understand that it is probably in the best interest of the devices to
not pick stupid defaults. But it is also probably in the best interest
of the driver to set those params, and if the driver is going to set its
values, the devices defaults are moot unless we assume that those may end
up being used by the driver as a hint when deciding which parameter
values to choose.

What am I missing here?

Regards,
Halil