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[85.204.121.218]) by smtp.gmail.com with ESMTPSA id e17sm3975147ljj.104.2019.10.19.09.56.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Oct 2019 09:56:52 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 40D5E1804C8; Sat, 19 Oct 2019 18:56:51 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Sebastian Moeller , Johannes Berg Cc: Kan Yan , Make-Wifi-fast In-Reply-To: References: <157115993755.2500430.12214017471129215800.stgit@toke.dk> <157115994190.2500430.14955682016008497593.stgit@toke.dk> <87o8yfg0zo.fsf@toke.dk> <751EA059-654B-4E06-A3D6-C727FE1FCE98@gmx.de> <87lftjfz51.fsf@toke.dk> <18FC6F1D-084C-44BD-87E7-C9F394D6FCD1@gmx.de> <32a96b6ad48387876b7125adba147578564d297a.camel@sipsolutions.net> <661B8FD5-510B-4DC5-A080-F04CA1C10C71@gmx.de> <87imolc4p9.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Sat, 19 Oct 2019 18:56:51 +0200 Message-ID: <87a79wd67g.fsf@toke.dk> MIME-Version: 1.0 X-MC-Unique: g91FTGesPV-0sIypndzarg-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Make-wifi-fast] [PATCH v2 4/4] mac80211: Use Airtime-based Queue Limits (AQL) on packet dequeue X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 19 Oct 2019 16:56:56 -0000 Sebastian Moeller writes: > On October 19, 2019 2:14:42 PM GMT+02:00, "Toke H=C3=B8iland-J=C3=B8rgens= en" wrote: >>Sebastian Moeller writes: >> >>>> On Oct 18, 2019, at 16:15, Johannes Berg >>wrote: >>>>=20 >>>> On Thu, 2019-10-17 at 18:11 -0700, Kan Yan wrote: >>>>> I don't think it is hard to take care of extra header size for >>frames >>>>> with VLAN tags >>>>=20 >>>> VLAN tags are payload as far as wifi is concerned, so no need to >>take >>>> that into account ... >>> >>> =09Ah, good to know; but just out of curiosity is any of the >>> =09following 7 Byte Preamble + 1 Byte start of frame delimiter >>> =09(SFD) + 12 Byte inter frame gap (IFG) actually packaged into >>> =09ethernet frames inside 802.11 packets? I would have guessed that >>> =09at least the IFG would be dropped as it does not really exist as >>> =09"data"? >> >>No, those are accounted in the airtime calculation in airtime.c (Felix' >>code). E.g.,: >> >>=09=09duration =3D 20 + 16; /* premable + SIFS */ > > > Looks like apples and pears to me. These seem to be the wifi preamble > and short interframe space in microseconds. Sure you need to add those > to the airtime estimate as these will hog airtime. > > But the 12 byte interframe gap of the Ethernet packets that are > transmitted over a 802.11 link surely will not be actually transmitted > as a stretch of zeros? Same for the Ethernet preamble and the start of > frame marker, as those can/will be trivially added by the Ethernet NIC > that will handle the encapsulated Ethernet frame after the wifi link, > no? > > As far as I can tell, the wifi SIFS is constant time independent of > wifi link speed while the IFG size is constant but it's duration is > not? > > Again, I am trying to understand this conceptually, which seems > orthogonal to the question of whether 38 is the correct number.... > > Best Regards > Sebastian > > P.S.: Is there a repository I could look into to try to figure this > out myself? This paper has a fairly comprehensive description of how frames look when transmitted over the air: http://dx.doi.org/10.1155/2015/548109 (see Figure 1 and Table 2, and the text in Section 2). Otherwise you'll have to go read the standards, I guess (though I can't say I'd recommend it as light reading :P) -Toke