linux-kernel - Re: [PATCH] selftests/resctrl: fix clang build warnings related to abs(), labs() calls

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Date: Fri, 3 May 2024 09:52:49 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Shuah Khan <shuah@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 Fenghua Yu <fenghua.yu@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>,
 Valentin Obst <kernel@...entinobst.de>, linux-kselftest@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH] selftests/resctrl: fix clang build warnings related to
 abs(), labs() calls

On 5/3/24 1:00 AM, Ilpo Järvinen wrote:
> On Thu, 2 May 2024, John Hubbard wrote:
..
>> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
>> index d67ffa3ec63a..c873793d016d 100644
>> --- a/tools/testing/selftests/resctrl/mbm_test.c
>> +++ b/tools/testing/selftests/resctrl/mbm_test.c
>> @@ -33,7 +33,7 @@ show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span)
>>   
>>   	avg_bw_imc = sum_bw_imc / 4;
>>   	avg_bw_resc = sum_bw_resc / 4;
>> -	avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc;
>> +	avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc;
>>   	avg_diff_per = (int)(avg_diff * 100);
>>   
>>   	ret = avg_diff_per > MAX_DIFF_PERCENT;
> 
> But how are these two cases same after your change when you ended up
> removing taking the absolute value entirely?

All of the arguments are unsigned integers, so all arithmetic results
are interpreted as unsigned, so taking the absolute value of that is
always a no-op.

thanks,
-- 
John Hubbard
NVIDIA