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From b8864890b18903936a68cda65ed1401703a2c67f Mon Sep 17 00:00:00 2001
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From: Andrea Claudi <aclaudi@redhat.com>
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Date: Tue, 21 Apr 2020 14:32:49 +0200
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Subject: [PATCH] man: Clarify idleslope calculation for tc-cbs
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1557461
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Upstream Status: iproute2.git commit 1915af404fdbf
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commit 1915af404fdbfbfef915078cec57d7425f500dd2
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Author: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
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Date: Fri Nov 10 14:34:36 2017 -0800
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man: Clarify idleslope calculation for tc-cbs
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In order to calculate the idleSlope parameter of CBS correctly, users
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must take into account the entire packet size, including the overhead
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from all layers.
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Add some more details to the man page to clarify that, giving one
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simple example and pointing users to the correct 802.1Q section for
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further clarifications if needed.
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Signed-off-by: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>
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---
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man/man8/tc-cbs.8 | 14 +++++++++++++-
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1 file changed, 13 insertions(+), 1 deletion(-)
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diff --git a/man/man8/tc-cbs.8 b/man/man8/tc-cbs.8
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index 97e00c84ded16..32e1e0d4089fb 100644
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--- a/man/man8/tc-cbs.8
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+++ b/man/man8/tc-cbs.8
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@@ -43,7 +43,19 @@ second) when there is at least one packet waiting for transmission.
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Packets are transmitted when the current value of credits is equal or
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greater than zero. When there is no packet to be transmitted the
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amount of credits is set to zero. This is the main tunable of the CBS
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-algorithm.
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+algorithm and represents the bandwidth that will be consumed.
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+Note that when calculating idleslope, the entire packet size must be
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+considered, including headers from all layers (i.e. MAC framing and any
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+overhead from the physical layer), as described by IEEE 802.1Q-2014
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+section 34.4.
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+
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+As an example, for an ethernet frame carrying 284 bytes of payload,
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+and with no VLAN tags, you must add 14 bytes for the Ethernet headers,
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+4 bytes for the Frame check sequence (CRC), and 20 bytes for the L1
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+overhead: 12 bytes of interpacket gap, 7 bytes of preamble and 1 byte
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+of start of frame delimiter. That results in 322 bytes for the total
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+packet size, which is then used for calculating the idleslope.
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+
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.TP
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sendslope
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Sendslope is the rate of credits that is depleted (it should be a
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--
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2.25.3
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