From:   Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
To:     Johannes Berg <johannes@sipsolutions.net>
CC:     "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
        Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Subject: Re: question: crda timeout in cfg80211
Thread-Topic: question: crda timeout in cfg80211
Thread-Index: AQHU49FUZcg4gTfb8k6NNfp7UvpVxKYytK3mgADiKwA=
Date:   Tue, 9 Apr 2019 08:35:57 +0000
Message-ID: <20190409083551.g27qvcxqhfm2x4uq@bars>
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> > Linux cfg80211 regulatory subsystem uses CRDA timeout to ensure complet=
ion
> > of regulatory updates, performed by user-space software. See call_crda
> > functon in net/wireless/reg.c:
> >
> > static int call_crda(const char *alpha2)
> > {
> >       ...
> >
> >       queue_delayed_work(system_power_efficient_wq,
> >                       &crda_timeout, msecs_to_jiffies(3142));
> >       return 0;
> > }
> >
> > So regulatory update/reset operations shall be completed in 3142 msec.
> > And that includes processing of regulatory notifiers for all the
> > wireless cards in the system.
> >
> > It is not quite clear where this specific timeout value came from.
> > Original commit (a90c7a313a1c5b) doesn't go into details about it.
> >
> > Any ideas where it could come from ?
>=20
> No particular reason. It's just ~pi seconds, and IIRC Luis thought that
> was funny :-)

Indeed, it is PI. I should have known. But instead I spent some time
digging through 802.11 specs :)

> Are you seeing any issues with that?
=20
Well, as I mentioned in my question, regulatory update/reset operations
shall be completed in ~pi seconds for _all_ the wireless cards in the
system. In our case, regulatory reset operation may be fairly costly.
As a result, we end up with recurring reset timeout, when more than one
qtn card is installed in a single pcie host. One option for us is to
optimize regulatory reset operations in firmware.

But what do you think about converting crda_timeout into a per-wiphy
timeout in the case when all wiphy-s are being processed, e.g.
in update_all_wiphy_regulatory.

Regards,
Sergey