Received-SPF: pass (google.com: best guess record for domain of linux-wireless-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Kan Yan <kyan@google.com>
Cc:     Dave Taht <dave.taht@gmail.com>,
        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>,
        Johannes Berg <johannes@sipsolutions.net>,
        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: <CA+iem5tpfEmaWJ5Mw7xF9fb=XLceZpC1LM4Avo89Mn1fL7YZVw@mail.gmail.com>
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>
Date:   Thu, 21 Nov 2019 11:05:16 +0100
Message-ID: <87a78p8rz7.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=WINDOWS-1252
Content-Transfer-Encoding: quoted-printable
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

Kan Yan <kyan@google.com> writes:

>> It would be interesting to get some samples of the actual sojourn time
>> as seen by CoDel in mac80211. Might be doable with bpftrace...
>
> I will try to add some trace event to get the sojourn time for the
> next round of tests.

In theory, this ought to produce a histogram of sojourn times (in
microseconds):

bpftrace -e 'kretprobe:codel_skb_time_func { @sojourn =3D lhist((nsecs - (r=
etval << 10))/1000, 0, 100000, 1000); }'


Can't get the CoDel drop mechanism to trigger on my system at all,
though (a laptop running on iwl). I guess because there's queue
backpressure to userspace first?

It would be interesting to see if it works for you, assuming you can get
bpftrace to work on your test system :)

-Toke