Adding upstream version 6.1.0.upstream/6.1.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 163 insertions, 0 deletions

diff --git a/man/man8/tc-stab.8 b/man/man8/tc-stab.8
new file mode 100644
index 0000000..03a0659
--- /dev/null
+++ b/man/man8/tc-stab.8
@@ -0,0 +1,163 @@
+.TH STAB 8 "31 October 2011" iproute2 Linux
+.
+.SH NAME
+tc\-stab \- Generic size table manipulations
+.
+.SH SYNOPSIS
+.nf
+tc qdisc add ... stab
+.RS 4
+[ \fBmtu\fR BYTES ] [ \fBtsize\fR SLOTS ]
+[ \fBmpu\fR BYTES ] [ \fBoverhead\fR BYTES ]
+[ \fBlinklayer\fR { adsl | atm | ethernet } ] ...
+.RE
+.fi
+
+.SH OPTIONS
+For the description of BYTES \- please refer to the \fBUNITS\fR
+section of \fBtc\fR(8).
+
+.IP \fBmtu\fR 4
+.br
+maximum packet size we create size table for, assumed 2048 if not specified explicitly
+.IP \fBtsize\fR
+.br
+required table size, assumed 512 if not specified explicitly
+.IP \fBmpu\fR
+.br
+minimum packet size used in computations
+.IP \fBoverhead\fR
+.br
+per\-packet size overhead (can be negative) used in computations
+.IP \fBlinklayer\fR
+.br
+required linklayer specification.
+.PP
+.
+.SH DESCRIPTION
+.
+Size tables allow manipulation of packet sizes, as seen by the whole scheduler
+framework (of course, the actual packet size remains the same). Adjusted packet
+size is calculated only once \- when a qdisc enqueues the packet. Initial root
+enqueue initializes it to the real packet's size.
+
+Each qdisc can use a different size table, but the adjusted size is stored in
+an area shared by whole qdisc hierarchy attached to the interface. The effect is
+that if you have such a setup, the last qdisc with a stab in a chain "wins". For
+example, consider HFSC with simple pfifo attached to one of its leaf classes.
+If that pfifo qdisc has stab defined, it will override lengths calculated
+during HFSC's enqueue; and in turn, whenever HFSC tries to dequeue a packet, it
+will use a potentially invalid size in its calculations. Normal setups will
+usually include stab defined only on root qdisc, but further overriding gives
+extra flexibility for less usual setups.
+
+The initial size table is calculated by \fBtc\fR tool using \fBmtu\fR and
+\fBtsize\fR parameters. The algorithm sets each slot's size to the smallest
+power of 2 value, so the whole \fBmtu\fR is covered by the size table. Neither
+\fBtsize\fR, nor \fBmtu\fR have to be power of 2 value, so the size
+table will usually support more than is required by \fBmtu\fR.
+
+For example, with \fBmtu\fR\~=\~1500 and \fBtsize\fR\~=\~128, a table with 128
+slots will be created, where slot 0 will correspond to sizes 0\-16, slot 1 to
+17\~\-\~32, \&..., slot 127 to 2033\~\-\~2048. Sizes assigned to each slot
+depend on \fBlinklayer\fR parameter.
+
+Stab calculation is also safe for an unusual case, when a size assigned to a
+slot would be larger than 2^16\-1 (you will lose the accuracy though).
+
+During the kernel part of packet size adjustment, \fBoverhead\fR will be added
+to original size, and then slot will be calculated. If the size would cause
+overflow, more than 1 slot will be used to get the final size. This of course
+will affect accuracy, but it's only a guard against unusual situations.
+
+Currently there are two methods of creating values stored in the size table \-
+ethernet and atm (adsl):
+
+.IP ethernet 4
+.br
+This is basically 1\-1 mapping, so following our example from above
+(disregarding \fBmpu\fR for a moment) slot 0 would have 8, slot 1 would have 16
+and so on, up to slot 127 with 2048. Note, that \fBmpu\fR\~>\~0 must be
+specified, and slots that would get less than specified by \fBmpu\fR will get
+\fBmpu\fR instead. If you don't specify \fBmpu\fR, the size table will not be
+created at all (it wouldn't make any difference), although any \fBoverhead\fR
+value will be respected during calculations.
+.IP "atm, adsl"
+.br
+ATM linklayer consists of 53 byte cells, where each of them provides 48 bytes
+for payload. Also all the cells must be fully utilized, thus the last one is
+padded if/as necessary.
+
+When the size table is calculated, adjusted size that fits properly into lowest
+amount of cells is assigned to a slot. For example, a 100 byte long packet
+requires three 48\-byte payloads, so the final size would require 3 ATM cells
+\- 159 bytes.
+
+For ATM size tables, 16\~bytes sized slots are perfectly enough. The default
+values of \fBmtu\fR and \fBtsize\fR create 4\~bytes sized slots.
+.PP
+.
+.SH "TYPICAL OVERHEADS"
+The following values are typical for different adsl scenarios (based on
+\fB[1]\fR and \fB[2]\fR):
+
+.nf
+LLC based:
+.RS 4
+PPPoA \- 14 (PPP \- 2, ATM \- 12)
+PPPoE \- 40+ (PPPoE \- 8, ATM \- 18, ethernet 14, possibly FCS \- 4+padding)
+Bridged \- 32 (ATM \- 18, ethernet 14, possibly FCS \- 4+padding)
+IPoA \- 16 (ATM \- 16)
+.RE
+
+VC Mux based:
+.RS 4
+PPPoA \- 10 (PPP \- 2, ATM \- 8)
+PPPoE \- 32+ (PPPoE \- 8, ATM \- 10, ethernet 14, possibly FCS \- 4+padding)
+Bridged \- 24+ (ATM \- 10, ethernet 14, possibly FCS \- 4+padding)
+IPoA \- 8 (ATM \- 8)
+.RE
+.fi
+There are a few important things regarding the above overheads:
+.
+.IP \(bu 4
+IPoA in LLC case requires SNAP, instead of LLC\-NLPID (see rfc2684) \- this is
+the reason why it actually takes more space than PPPoA.
+.IP \(bu
+In rare cases, FCS might be preserved on protocols that include Ethernet frames
+(Bridged and PPPoE). In such situation, any Ethernet specific padding
+guaranteeing 64 bytes long frame size has to be included as well (see RFC2684).
+In the other words, it also guarantees that any packet you send will take
+minimum 2 atm cells. You should set \fBmpu\fR accordingly for that.
+.IP \(bu
+When the size table is consulted, and you're shaping traffic for the sake of
+another modem/router, an Ethernet header (without padding) will already be added
+to initial packet's length. You should compensate for that by subtracting 14
+from the above overheads in this case. If you're shaping directly on the router
+(for example, with speedtouch usb modem) using ppp daemon, you're using raw ip
+interface without underlying layer2, so nothing will be added.
+
+For more thorough explanations, please see \fB[1]\fR and \fB[2]\fR.
+.
+.SH "ETHERNET CARDS CONSIDERATIONS"
+.
+It's often forgotten that modern network cards (even cheap ones on desktop
+motherboards) and/or their drivers often support different offloading
+mechanisms. In the context of traffic shaping, 'tso' and 'gso' might cause
+undesirable effects, due to massive TCP segments being considered during
+traffic shaping (including stab calculations). For slow uplink interfaces,
+it's good to use \fBethtool\fR to turn off offloading features.
+.
+.SH "SEE ALSO"
+.
+\fBtc\fR(8), \fBtc\-hfsc\fR(7), \fBtc\-hfsc\fR(8),
+.br
+\fB[1]\fR http://ace\-host.stuart.id.au/russell/files/tc/tc\-atm/
+.br
+\fB[2]\fR http://www.faqs.org/rfcs/rfc2684.html
+
+Please direct bugreports and patches to: <netdev@vger.kernel.org>
+.
+.SH "AUTHOR"
+.
+Manpage created by Michal Soltys (soltys@ziu.info)