From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Johannes Berg <johannes@sipsolutions.net>,
Jens Axboe <axboe@kernel.dk>,
Emmanuel Grumbach <emmanuel.grumbach@intel.com>,
Luca Coelho <luciano.coelho@intel.com>
Cc: "linux-wireless\@vger.kernel.org"
<linux-wireless@vger.kernel.org>,
Networking <netdev@vger.kernel.org>
Subject: Re: iwlwifi warnings in 5.5-rc1
Date: Wed, 11 Dec 2019 15:02:26 +0100 [thread overview]
Message-ID: <87tv67ez9p.fsf@toke.dk> (raw)
In-Reply-To: <bfab4987668990ea8d86a98f3e87c3fa31403745.camel@sipsolutions.net>
Johannes Berg <johannes@sipsolutions.net> writes:
> Hi Toke,
>
>> > OK, I talked with Emmanuel and I think it's the GSO path - it'll end up
>> > with skb_clone() and then report both of them back.
>>
>> Right, figured it was something like that; just couldn't find the place
>> in the driver where it did that from my cursory browsing.
>
> Yeah, deeply hidden in the guts :)
>
>> > Regardless, I think I'll probably have to disable AQL and make it more
>> > opt-in for the driver - I found a bunch of other issues ...
>>
>> Issues like what? Making it opt-in was going to be my backup plan; I was
>> kinda hoping we could work out any issues so it would be a "no harm"
>> kind of thing that could be left as always-on. Maybe that was a bit too
>> optimistic; but it's also a pain having to keep track of which drivers
>> have which features/fixes...
>
> Sorry to keep you in suspense, had to run when I sent that email and
> didn't have time to elaborate.
>
> 1) Hardware building A-MPDU will probably make the airtime estimate
> quite a bit wrong. Maybe this doesn't matter? But I wasn't sure how
> this works now with ath10k where (most of?) the testing was.
Yeah, not too worried about this...
> 2) GSO/TSO like what we have - it's not really clear how to handle it.
> The airtime estimate will shoot *way* up (64kB frame) once that frame
> enters, and then ... should it "trickle back down" as the generated
> parts are transmitted? But then the driver needs to split up the
> airtime estimate? Or should it just go back down entirely? On the
> first frame? That might overshoot. On the last frame? Opposite
> problem ...
Well, ideally it would be divided out over the component packets; but
yeah, who is going to do that? I think reporting it on the first packet
would be the safest if we had to choose. Also, ideally we would want the
GSO/TSO mechanism to lower the size of the superpackets at lower rates
(does it?). At higher rates this matters less...
> 3) I'm not quite convinced that all drivers report the TX rate
> completely correctly in the status, some don't even use this path
> but the ieee80211_tx_status_ext() which doesn't update the rate.
>
> 4) Probably most importantly, this is completely broken with HE because
> there's currently no way to report HE rates in the TX status at all!
> I just worked around that in our driver for 'iw' reporting purposes
> by implementing the rate reporting in the sta_statistics callback,
> but that data won't be used by the airtime estimates.
Hmm, yeah, both of those are good points. I guess I just kinda assumed
that the drivers were already doing the right thing there... :)
> Now, (1) probably doesn't matter, the estimates don't need to be that
> accurate. (2) I'm not sure how to solve; (3) and (4) could both be
> solved by having some mechanism of the rate scaling to tell us what the
> current rate is whenever it updates, rather than relying on the
> last_rate. Really we should do that much more, and even phase out
> last_rate entirely, it's a stupid concept.
Yes, that last bit would be good!
> There's an additional wrinkle here - what about HE scheduled mode, where
> the AP decided when and at what rate you're allowed to send? We don't
> report that at all, not even as part of rate scaling, since rate scaling
> only affects *our* decision, not when we send as a response to a trigger
> frame. This is _still_ relevant for AQL, but there we can only see what
> the AP used last (**), but we don't track that now nor do we track the
> proportion of packets that we sent triggered vs. normal medium
> access...
Huh, wasn't aware that was a thing in HE; that's cool! And yeah, could
have interesting interactions with AQL...
-Toke
next prev parent reply other threads:[~2019-12-11 14:02 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 20:46 iwlwifi warnings in 5.5-rc1 Jens Axboe
2019-12-11 8:36 ` Johannes Berg
2019-12-11 8:53 ` Toke Høiland-Jørgensen
2019-12-11 10:11 ` Johannes Berg
2019-12-11 10:23 ` Toke Høiland-Jørgensen
2019-12-11 11:51 ` Johannes Berg
2019-12-11 13:42 ` Johannes Berg
2019-12-11 14:04 ` Toke Høiland-Jørgensen
2019-12-11 14:12 ` Johannes Berg
2019-12-11 14:47 ` Toke Høiland-Jørgensen
2019-12-11 21:18 ` Johannes Berg
2019-12-12 10:45 ` Toke Høiland-Jørgensen
2019-12-11 14:02 ` Toke Høiland-Jørgensen [this message]
2019-12-11 21:17 ` Johannes Berg
2019-12-12 10:55 ` Toke Høiland-Jørgensen
2019-12-12 11:00 ` Johannes Berg
2019-12-21 0:55 ` Jens Axboe
2019-12-21 9:17 ` Johannes Berg
2019-12-21 13:45 ` Jens Axboe
2019-12-11 13:45 ` Johannes Berg
2019-12-11 14:09 ` Toke Høiland-Jørgensen
2019-12-11 14:13 ` Johannes Berg
2019-12-11 14:55 ` Toke Høiland-Jørgensen
2019-12-11 21:19 ` Johannes Berg
2019-12-12 10:55 ` Toke Høiland-Jørgensen
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