The offending iproute2 commit appears to be:
commit d947f365602b30657d1b797e7464000d0ab88d5a
Author: Jonathan Lennox <[email protected]>
Date: Wed Feb 26 18:53:21 2025 +0000
tc: Fix rounding in tc_calc_xmittime and tc_calc_xmitsize.
Currently, tc_calc_xmittime and tc_calc_xmitsize round from double to
int three times — once when they call tc_core_time2tick /
tc_core_tick2time (whose argument is int), once when those functions
return (their return value is int), and then finally when the tc_calc_*
functions return. This leads to extremely granular and inaccurate
conversions.
As a result, for example, on my test system (where tick_in_usec=15.625,
clock_factor=1, and hz=1000000000) for a bitrate of 1Gbps, all tc htb
burst values between 0 and 999 bytes get encoded as 0 ticks; all values
between 1000 and 1999 bytes get encoded as 15 ticks (equivalent to 960
bytes); all values between 2000 and 2999 bytes as 31 ticks (1984 bytes);
etc.
The patch changes the code so these calculations are done internally in
floating-point, and only rounded to integer values when the value is
returned. It also changes tc_calc_xmittime to round its calculated value
up, rather than down, to ensure that the calculated time is actually
sufficient for the requested size.
Signed-off-by: Jonathan Lennox <[email protected]>
Signed-off-by: David Ahern <[email protected]>
It looks like a deliberate change of behavior.
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https://bugs.launchpad.net/bugs/2129005
Title:
tc class show dev provides incorrect value for cburst
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