From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Furniss Date: Tue, 23 Sep 2014 19:05:52 +0000 Subject: Re: [Cerowrt-devel] Correctly calculating overheads on unknown connections Message-Id: <5421C490.3020104@gmail.com> List-Id: References: <6DF5DFA0-D88E-470E-ACB6-37703EA964E7@gmx.de> In-Reply-To: <6DF5DFA0-D88E-470E-ACB6-37703EA964E7@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable To: lartc@vger.kernel.org Sebastian Moeller wrote: > Hi Andy, > > On Sep 23, 2014, at 17:10 , Andy Furniss > wrote: > BUT if you look at the kernel code, stab does not automatically > include the ethernet overhead, so the subtract 14 in the above is > actually wrong. See > http://lxr.free-electrons.com/source/net/sched/sch_api.c#L538 where > =93pkt_len =3D skb->len + stab->szopts.overhead; is used instead of using > =93qdisc_skb_cb(skb)->pkt_len=94 that as filled properly in > http://lxr.free-electrons.com/source/net/core/dev.c#L2705 . At least > to me this clearly looks like the ethernet overhead is not pre-added > when using stab, but I could be wrong. And on an ADSL link you can > see this quite well, with the proper overhead values sqm-scripts > still controls the latency under netperf-wrapper=92s RRUL test nicely > even if the shaping rate equals the line rate, with the overhead to > small latency goes down the drain ;) I guess skb->len varies depending on the interface. Anyway here's a quick test on my desktop PC running a git kernel and tc. I used to shape remotely pppoa/vc mux dsl so know that for me ping -s 10 .... =3D one cell and -s 11 =3D 2 cells - overhead on IP was 10. Paste time - ph4[/mnt/sda8/Qos/stab-tests]# cat stab-hfsc #set -x TC=3D/sbin/tc $TC qdisc del dev eth0 root &>/dev/null if [ "$1" =3D "stop" ] then exit fi $TC qdisc add dev eth0 root handle 1: stab overhead -4 linklayer atm=20 hfsc default ffff $TC class add dev eth0 parent 1: classid 1:1 hfsc sc rate 1kbit ul rate=20 1kbit $TC qdisc add dev eth0 parent 1:1 pfifo limit 200 $TC class add dev eth0 parent 1:0 classid 1:ffff hfsc sc rate 80mbit ul=20 rate 80mbit $TC filter add dev eth0 parent 1: protocol ip prio 1 \ u32 match ip protocol 1 0xff classid 1:1 ph4[/mnt/sda8/Qos/stab-tests]# ./stab-hfsc ph4[/mnt/sda8/Qos/stab-tests]# ping -s 10 -c 1 noki PING noki.andys.lan (192.168.0.1) 10(38) bytes of data. 18 bytes from noki.andys.lan (192.168.0.1): icmp_req=3D1 ttld --- noki.andys.lan ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms ph4[/mnt/sda8/Qos/stab-tests]# tc -s qdisc ls dev eth0 qdisc hfsc 1: root refcnt 2 default ffff Sent 106 bytes 2 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 qdisc pfifo 8005: parent 1:1 limit 200p Sent 53 bytes 1 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 ph4[/mnt/sda8/Qos/stab-tests]# ./stab-hfsc ph4[/mnt/sda8/Qos/stab-tests]# ping -s 11 -c 1 noki PING noki.andys.lan (192.168.0.1) 11(39) bytes of data. 19 bytes from noki.andys.lan (192.168.0.1): icmp_req=3D1 ttld --- noki.andys.lan ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms ph4[/mnt/sda8/Qos/stab-tests]# tc -s qdisc ls dev eth0 qdisc hfsc 1: root refcnt 2 default ffff Sent 106 bytes 1 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 qdisc pfifo 8006: parent 1:1 limit 200p Sent 106 bytes 1 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0 ph4[/mnt/sda8/Qos/stab-tests]# So it seems that overhead -4 is the correct thing to do. I also tested backlogged (-i 0.2) with -s 10 and 11 and tcpdump showed=20 the correct deltas - ph4[/mnt/sda8/Qos/stab-tests]# tcpdump -nnttti eth0 icmp and dst host noki snip 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 92, length 18 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 93, length 18 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 94, length 18 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 95, length 18 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 96, length 18 00:00:00.424001 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 97, length 18 00:00:00.423999 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1345, seq 98, length 18 00:00:00.424000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 1, length 19 00:00:00.848000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 2, length 19 00:00:00.848001 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 3, length 19 00:00:00.847999 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 4, length 19 00:00:00.848000 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 5, length 19 00:00:00.847999 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 6, length 19 00:00:00.848002 IP 192.168.0.3 > 192.168.0.1: ICMP echo request, id=20 1347, seq 7, length 19