iproute2: tc.8: update UNITS section.

- rename section UNITS to PARAMETERS.
- break section PARAMETERS down to four subsections to cover the
  common used parameter types(RATES, TIMES, SIZES, VALUES).
- add some explaination for IEC units in RATES.
- point out the max value we can set for RATES, TIMES and SIZES.

Signed-off-by: Li Wei <lw@cn.fujitsu.com>

man/man8/tc.8

@@ -257,10 +257,32 @@ qdiscs applies.
 FILTERS
 Filters have a three part ID, which is only needed when using a hashed
 filter hierarchy.
-.SH UNITS
-All parameters accept a floating point number, possibly followed by a unit.
-.P
-Bandwidths or rates can be specified in:
+
+.SH PARAMETERS
+The following parameters are widely used in TC. For other parameters,
+see the man pages for individual qdiscs.
+
+.TP
+RATES
+Bandwidths or rates.
+These parameters accept a floating point number, possibly followed by
+a unit (both SI and IEC units supported).
+.RS
+.TP
+bit or a bare number
+Bits per second
+.TP
+kbit
+Kilobits per second
+.TP
+mbit
+Megabits per second
+.TP
+gbit
+Gigabits per second
+.TP
+tbit
+Terabits per second
 .TP
 bps
 Bytes per second
@@ -271,33 +293,26 @@ Kilobytes per second
 mbps
 Megabytes per second
 .TP
-kbit
-Kilobits per second
+gbps
+Gigabytes per second
 .TP
-mbit
-Megabits per second
-.TP
-bit or a bare number
-Bits per second
+tbps
+Terabytes per second
+
 .P
-Amounts of data can be specified in:
-.TP
-kb or k
-Kilobytes
-.TP
-mb or m
-Megabytes
-.TP
-mbit
-Megabits
-.TP
-kbit
-Kilobits
-.TP
-b or a bare number
-Bytes.
+To specify in IEC units, replace the SI prefix (k-, m-, g-, t-) with
+IEC prefix (ki-, mi-, gi- and ti-) respectively.
+
 .P
-Lengths of time can be specified in:
+TC store rates as a 32-bit unsigned integer in bps internally,
+so we can specify a max rate of 4294967295 bps.
+.RE
+
+.TP
+TIMES
+Length of time. Can be specified as a floating point number
+followed by an optional unit:
+.RS
 .TP
 s, sec or secs
 Whole seconds
@@ -308,6 +323,51 @@ Milliseconds
 us, usec, usecs or a bare number
 Microseconds.
 
+.P
+TC defined its own time unit (equal to microsecond) and stores
+time values as 32-bit unsigned integer, thus we can specify a max time value
+of 4294967295 usecs.
+.RE
+
+.TP
+SIZES
+Amounts of data. Can be specified as a floating point number
+followed by an optional unit:
+.RS
+.TP
+b or a bare number
+Bytes.
+.TP
+kbit
+Kilobits
+.TP
+kb or k
+Kilobytes
+.TP
+mbit
+Megabits
+.TP
+mb or m
+Megabytes
+.TP
+gbit
+Gigabits
+.TP
+gb or g
+Gigabytes
+
+.P
+TC stores sizes internally as 32-bit unsigned integer in byte,
+so we can specify a max size of 4294967295 bytes.
+.RE
+
+.TP
+VALUES
+Other values without a unit.
+These parameters are interpreted as decimal by default, but you can
+indicate TC to interpret them as octal and hexadecimal by adding a '0'
+or '0x' prefix respectively.
+
 .SH TC COMMANDS
 The following commands are available for qdiscs, classes and filter:
 .TP