On 5/3/2024 9:52 AM, John Hubbard wrote:
> 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.
It does not seem as though clang can see when values have been casted.
I tried to do so explicitly with a:
avg_diff = labs((long)avg_bw_resc - avg_bw_imc) / (float)avg_bw_imc;
But that still triggers:
warning: taking the absolute value of unsigned type 'unsigned long' has no effect [-Wabsolute-value]
Looks like we may need to be more explicit types and not rely on casting so much
to make the compiler happy.
Reinette