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

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Message-Id: <CE75595B-3281-404F-A208-1664D5B004D6@8x8.com>
Date: Tue, 18 Feb 2025 15:10:26 -0500
From: Jonathan Lennox <jonathan.lennox@....com>
To: Stephen Hemminger <stephen@...workplumber.org>
Cc: netdev@...r.kernel.org
Subject: Re: [PATCH iproute2] tc: Fix rounding in tc_calc_xmittime and
 tc_calc_xmitsize.

> On Feb 17, 2025, at 1:14 AM, Stephen Hemminger <stephen@...workplumber.org> wrote:
> 
> On Wed, 5 Feb 2025 16:16:21 -0500
> Jonathan Lennox <jonathan.lennox@....com> wrote:
> 
>> The logic in tc that converts between sizes and times for a given rate (the
>> functions tc_calc_xmittime and tc_calc_xmitsize) suffers from double rounding,
>> with intermediate values getting cast to unsigned int.
> 
> The concept makes sense, but is missing a valid Signed-Off-by: and therefore
> needs to be resent.

Thanks, will fix in v2.

> Also, you don't need to rename the functions, why not always use floating point

There was another function using tc_calc_xmittime (tbv_print_opt) so I was worried
about breaking it, but on inspection I realize it’s also doing a calculation in double
and it’s just printing data, so it should be fine (and hopefully an improvement).

I’ve fixed this in v2 as well.