netdev - Re: [PATCH iproute2 v2] tc: Fix rounding in tc_calc_xmittime and tc_calc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5b9f16c1-450c-4a39-be2c-634b4f1864b5@kernel.org>
Date: Mon, 24 Feb 2025 09:58:13 -0700
From: David Ahern <dsahern@...nel.org>
To: Jonathan Lennox <jonathan.lennox@....com>
Cc: netdev@...r.kernel.org, Stephen Hemminger <stephen@...workplumber.org>
Subject: Re: [PATCH iproute2 v2] tc: Fix rounding in tc_calc_xmittime and
 tc_calc_xmitsize.

On 2/24/25 9:36 AM, Jonathan Lennox wrote:

####

> The problem is that 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.

####

put that blurb as the commit message and re-send.

Thanks,

> 
> 
> Can you let me know the desired style for commit messages — how much of this
> explanation should be in it?  I can submit a v3 with the desired explanation in
> the commit message.
> 
> Thanks!
> 
> Jonathan Lennox
>