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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 May 2024 22:00:45.1769 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 10703489-1755-4b03-3b2c-08dc6bbc7bb6 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH3PEPF00000012.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8283 On 5/3/24 1:46 PM, Reinette Chatre wrote: > Hi John, > On 5/3/2024 12:12 PM, John Hubbard wrote: >> On 5/3/24 11:37 AM, Reinette Chatre wrote: >>> 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: >>>> ... ... >> I assumed that this code did not expect to handle negative numbers, >> because it is using unsigned math throughout. >> >> If you do expect it to handle cases where, for example, this happens: >> >>    avg_bw_imc > avg_bw_resc > > The existing code seems to handle this ok. A sample program with this > scenario comparing existing computation with your first proposal is > below: > > #include > #include > > void main(void) { > unsigned long avg_bw_resc = 20000; > unsigned long avg_bw_imc = 40000; > float avg_diff; > > /* Existing code */ > avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > printf("Existing code: avg_diff = %f\n", avg_diff); > > /* Original proposed fix */ > avg_diff = (float)(avg_bw_resc - avg_bw_imc) / avg_bw_imc; > printf("Original proposed fix: avg_diff = %f\n", avg_diff); > } > > output: > Existing code: avg_diff = 0.500000 > Original proposed fix: avg_diff = 461168590192640.000000 That seems "a little bit" wrong. haha :) > >> >> ...then a proper solution is easy, and looks like this: >> >> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c >> index c873793d016d..b87f91a41494 100644 >> --- a/tools/testing/selftests/resctrl/mbm_test.c >> +++ b/tools/testing/selftests/resctrl/mbm_test.c >> @@ -17,8 +17,8 @@ >>  static int >>  show_bw_info(unsigned long *bw_imc, unsigned long *bw_resc, size_t span) >>  { >> -       unsigned long avg_bw_imc = 0, avg_bw_resc = 0; >> -       unsigned long sum_bw_imc = 0, sum_bw_resc = 0; >> +       long avg_bw_imc = 0, avg_bw_resc = 0; >> +       long sum_bw_imc = 0, sum_bw_resc = 0; >>         int runs, ret, avg_diff_per; >>         float avg_diff = 0; >> >> Should I resend the patch with that approach? > > ok. That indeed makes the computations easier to understand. I assume > you intend to fix the snippet in mba_test.c also? > Yes, will do that. Thanks for spotting the bug in the original "fix"! thanks, -- John Hubbard NVIDIA