Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

Saxman58 — Wed, 17 Jul 2024 12:53:39 GMT

Thanks, Runar. Have a good vacation.

Glen

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

runsiv — Wed, 17 Jul 2024 07:20:28 GMT

Sounds good,

I will be out of office from Friday until mid august but I will hand this case over to co-worker.

Regards

Runar

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

Saxman58 — Tue, 16 Jul 2024 17:37:14 GMT

Thanks Runar,

I am examining the Zephyr and driver code and am hoping to find a way to know when I should pause sending to let the driver catch up. The information you sent is helpful. I'll leave this open and will report back when I've figured out the best way to handle this.

Glen

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

runsiv — Tue, 16 Jul 2024 10:21:16 GMT

Update: Is really just on short what I wrote above. we don't have flow control in Zephyr to make sure not to overwhelm the queues and not cause packet drops

Regards

Runar

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

runsiv — Tue, 16 Jul 2024 07:02:14 GMT

I will just forward the information I got from the Wi-Fi team first and then I will do another check regarding your post

[quote user=""]Is there a function to call to get the low level driver queue state?[/quote]

No public API, but we have this shell command wifi_util tx_stats 0 they can either use this command or call the code https://github.com/nrfconnect/sdk-nrf/blob/main/drivers/wifi/nrf700x/src/wifi_util.c#L265 from their program (please note that this isn't supposed to be called publicly, so, appropriate locking is missing and needs to be taken care)

This gives insight in to TX data path in the nRF70 driver.

[quote user=""]Is there a way to get a count of how many packets the tx_enqueue or tx_process functions are discarding? Maybe I could poll that as a way to infer when overflow is occurring. But I'd rather not have any overflow at all, because that means lost packets and I won't know which ones.[/quote]

These are part of the Wi-Fi statistics available via both SHELL wifi statistics and net-mgmt API: See the data structure https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/connectivity/networking/api/net_stats.html#c.net_stats_wifi and SHELL/API code https://github.com/nrfconnect/sdk-zephyr/blob/main/subsys/net/l2/wifi/wifi_shell.c#L881

errors.tx/rx -> Total dropped packets in nRF70 driver

[quote user=""]Is there maybe a callback or something that can send an event when the queue is getting close to full?[/quote]

Zephyr doesn't have a way for drivers to indicate to the networking stack (and there by applications) about the overflow on data queues and also ability stop/start (in Linux we have https://docs.kernel.org/networking/multiqueue.html#intro-kernel-support-for-multiqueue-devices and once a certain watermark is reached driver stops/starts the queues).

[quote user=""]Is there a way to make zsock_send() truly block if the downstream queue is full?[/quote]

There is unfortunately no per-packet feedback so my understanding it is not possible. However I will do another check with your question just to verify.

nRF70 driver does have a pending_q i.e., Queue to be used when nRF70 is busy and doesn't accept any further frames, but it has a build-time limit (for memory control), so, if Queue is full, it will start dropping packets.

I will update again as soon as I have something

Regards

Runar

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

Saxman58 — Mon, 15 Jul 2024 21:55:00 GMT

Thanks Runar. I look forward to the responses. It might help if I simplify or clarify my question a bit:

I understand that the packet data is passed between different queues and different threads. But it seems like the most direct way for this to work would be to have the application level zsock_send() block whenever the driver Wi-Fi queue is full if that is what the socket is connected to. Then we'd be guaranteed to not overflow the Wi-Fi queue since zsock_send() wouldn't execute until there was room for the packet to be sent.

RE: Wi-Fi driver throws out packets if sent too fast. How can we know when the driver queue is full so we can wait and not overload it?

runsiv — Mon, 15 Jul 2024 11:03:41 GMT

Hi Glen

I will have to ask internally regarding your questions and will get back to you when I have something

Regards

Runar