Re: Per MLO link TX stats

[Ben Greear <greearb@candelatech.com>]

On 8/27/24 08:56, Johannes Berg wrote:
> On Fri, 2024-07-12 at 10:52 -0700, Ben Greear wrote:
>> Hello,
>>
>> I've been trying to get better per MLO link stats.  I see that the rx path
>> stats are there, but in the tx path, I do not see anything other than 'deflink'
>> getting updated.
> 
> Yeah, nobody really cared too much about statistics yet. I know. Sorry.
> Not much time to work on it either now.
> 
>> And, at least with iwlwifi, I cannot find any way to actually see what link-id
>> was used to transmit a frame in the tx status callbacks (or anywhere else I looked).
> 
> You can probably derive that from the band for iwlwifi, since it only
> supports one active link on each 2.4 / 5 / 6 GHz if at all. And the band
> I guess you'd get from the LMAC ID or something. Should be in there
> somewhere... IOW, I think it's possible, but I'm also not entirely sure
> how we'd do it.

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.

>> 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.  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.

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.

Thanks,
Ben

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