Re: Per MLO link TX stats

[Ben Greear <greearb@candelatech.com>]

On 8/27/24 09:20, Johannes Berg wrote:
> On Tue, 2024-08-27 at 09:12 -0700, Ben Greear wrote:
>>
>> When be200 goes into eMLSR mode, both 5 and 6Ghz links are shown as active, so at least
>> you cannot use 'active link' to reliably update stats.
> 
> Sure, not active link - but there's an LMAC bit somewhere ... Ah, it's
> not documented, it's actually documented *differently*, but it should be
> bit 31 in len_n_flags in struct iwl_rx_packet.
> 
> Given the LMAC ID on the TX response notification we should know which
> LMAC transmitted it, and then I think it's a simple mapping to the
> active link. But I haven't actually really tried it.

If you can share a patch that documents this bit (like 0 means 5Ghz and 1 means 6Ghz??)
then we can try it out.

And maybe your idea for how to report it in tx-status too since that will touch
mac80211?

>>>> In the case where there is a single active link, then I can hack something together
>>>> that should be at least mostly right, but that won't fix any future radio that can
>>>> do 2+ active links.
>>>>
>>>> Any suggestions for best path forward on this?
>>>
>>> I really think we also need to do some work on the API/cfg80211 level,
>>> and have link station statistics in cfg80211 instead of full station,
>>> and then combine them to (older) userspace in cfg80211, i.e. if
>>> userspace doesn't request broken out per-link statistics. There's
>>> probably a bunch of work here, and I only have a vague idea of how it
>>> should be done...
>>
>> I think first step is to get the driver(s) able to report the link-id in
>> the tx-status.  After that, mac80211 can gather the stats.
> 
> Yeah, that makes sense, at least partially that's needed. I suspect that
> also we need to extend the API down to the sta_statistics call though to
> return per-link statistics, e.g. the TX bitrate would seem should be
> reported per link, and that's done through that call now I believe.

Yes.  At least at cfg80211 level, I think we should be able to query all
link stats in a single call into mac80211.  Down in mac80211, then per-link
stats structs appears to be how things are done now and seems like a good
solution.

> 
>> I hacked
>> tx/rx link stats into mac80211 ethtool (for first 3 links), but it is still not reliable since
>> mac80211 doesn't know the actual tx link id.
> 
> Right.
> 
>> After that, then certainly I'd be happy to have per-link stats available,
>> and combining them in cfg80211 seems like a fine idea as well.  Some things
>> that don't combine well (rssi, link rates, etc) would take a bit of kludging
>> if trying to provide a single 'sta' view of stats.
> 
> True, some can't just be added up and we'd have to find a sane different
> "best" view, perhaps for rates it'd be the better of the two or the sum
> if only reporting the bitrate, or better of the RSSI, etc. Case by case,
> I guess.

I'd suggest using highest active band when we have no better option for
summing/combining.

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com