Re: [PATCH] ofnet: Remove 200 ms timeout in get_card_packet to reduce input latency

[Daniel Kiper]

On Mon, May 06, 2024 at 10:34:22AM +0800, Michael Chang via Grub-devel wrote:
> When grub image is netbooted on ppc64le, the keyboard input exhibits
> significant latency, reports even say that characters are processed
> about once per second. This issue makes interactively trying to debug a
> ppc64le config very difficult.
>
> It seems that the latency is largely caused by a 200 ms timeout in the
> idle event loop, during which the network card interface is consistently
> polled for incoming packets. Often, no packets arrive during this
> period, so the timeout nearly always expires, which blocks the response
> to key inputs.
>
> Furthermore, this 200 ms timeout might not need to be enforced at this
> basic layer, considering that grub performs synchronous reads and its
> timeout management is actually handled by higher layers, not directly in
> the card instance. Additionally, the idle polling, which reacts to
> unsolicited packets like ICMP and SLAAC, would be fine at a less
> frequent polling interval, rather than needing a timeout for receiving a
> response.
>
> For these reasons, we believe the timeout in get_card_packet should be
> effectively removed. According to test results, the delay has
> disappeared, and it is now much easier to use interactively.
>
> Signed-Off-by: Michael Chang <mchang@suse.com>
> Tested-by: Tony Jones <tonyj@suse.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel