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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Johannes Berg <johannes@sipsolutions.net>,
        Kalle Valo <kvalo@codeaurora.org>, Kan Yan <kyan@google.com>
Cc:     Dave Taht <dave@taht.net>,
        Rajkumar Manoharan <rmanohar@codeaurora.org>,
        Kevin Hayes <kevinhayes@google.com>,
        Make-Wifi-fast <make-wifi-fast@lists.bufferbloat.net>,
        linux-wireless <linux-wireless@vger.kernel.org>,
        Yibo Zhao <yiboz@codeaurora.org>,
        John Crispin <john@phrozen.org>,
        Lorenzo Bianconi <lorenzo@kernel.org>,
        Felix Fietkau <nbd@nbd.name>
Subject: Re: [Make-wifi-fast] [PATCH v8 0/2] Implement Airtime-based Queue Limit (AQL)
In-Reply-To: <fa98f3b62454370ef6c1951571ba1789ac2679c3.camel@sipsolutions.net>
References: <20191115014846.126007-1-kyan@google.com> <CA+iem5vaeLR6v_nZ1YUZhfj32wF0DrvC2nyp8nb8qYAZLQjLdw@mail.gmail.com> <CAA93jw5wTbFV51oFJ6tFHLUMo=bau8fbU65k57bQjOHGJoCkkQ@mail.gmail.com> <CA+iem5s4ZY239Q4=Gwy3WrmVhcdhesirXph6XQoOP5w-nuWcYw@mail.gmail.com> <CAA93jw5t0TwBVv7_DVkJ_-NsVn0ODNHwU0orp2-+LPB45iFVoQ@mail.gmail.com> <CA+iem5uVJFcCYpJfhker-48XPrOf3a+NWr-nKnBtGmLX2yB_Lg@mail.gmail.com> <8736eiam8f.fsf@toke.dk> <CA+iem5tpfEmaWJ5Mw7xF9fb=XLceZpC1LM4Avo89Mn1fL7YZVw@mail.gmail.com> <87a78p8rz7.fsf@toke.dk> <CA+iem5tNz2jjEOVmbh3aPTXLLZfkRjZ60-+bon1vDEJ8D4hQJw@mail.gmail.com> <87muco5gv5.fsf@toke.dk> <CA+iem5sBPq0mfz+Qx+uJqCZ6t-Cjru+GCBcYExdu6JueUbBXyw@mail.gmail.com> <87eexvyoy8.fsf@toke.dk> <878so2m5gp.fsf@nemesis.taht.net> <CA+iem5vVGSJXeB8k2n32f=TvqncEj+bOjVbunWS0G8sm_MEosw@mail.gmail.com> <0101016ecf3bc899-6e391bba-96ed-4495-a7be-1aa8dd8f1bf2-000000@us-west-2.amazonses.com> <fa98f3b62454370ef6c1951571ba1789ac2679c3.camel@sipsolutions.net>
Date:   Wed, 04 Dec 2019 15:34:36 +0100
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Johannes Berg <johannes@sipsolutions.net> writes:

> On Wed, 2019-12-04 at 04:47 +0000, Kalle Valo wrote:
>>=20
>> > Overall, I think AQL and fq_codel works well, at least with ath10k.
>> > The current target value of 20 ms is a reasonable default.  It is
>> > relatively conservative that helps stations with weak signal to
>> > maintain stable throughput. Although, a debugfs entry that allows
>> > runtime adjustment of target value could be useful.
>>=20
>> Why not make it configurable via nl80211? We should use debugfs only for
>> testing and debugging, not in production builds, and to me the use case
>> for this value sounds like more than just testing.
>
> On the other hand, what application/tool or even user would be able to
> set this correctly?

Well, it's not inconceivable that someone might write a tool to
dynamically tune this; we do allow it to be changed at the qdisc layer
after all.

But until such a time as someone does that, I agree that it's not
terribly likely such a knob is going to see much use. As Kan's results
show, for inter-flow latency (like what the separate ping in his test is
showing), the FQ part takes care of the latency, and what's left there
is the AQL buffering. So I'm a little bit "meh" about this; wouldn't
object to making it a knob, but don't think I'm going to spend the time
writing that patch myself :)

-Toke