[DPDK/core Bug 1869] incorrect get_tsc_freq_arch() due to integer truncation

[DPDK/core Bug 1869] incorrect get_tsc_freq_arch() due to integer truncation

[bugzilla]

http://bugs.dpdk.org/show_bug.cgi?id=1869

            Bug ID: 1869
           Summary: incorrect get_tsc_freq_arch() due to integer
                    truncation
           Product: DPDK
           Version: unspecified
          Hardware: x86
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: core
          Assignee: dev@dpdk.org
          Reporter: rizzo.unipi@gmail.com
  Target Milestone: ---

There is a bug in
https://github.com/DPDK/dpdk/blob/main/lib/eal/x86/rte_cycles.c#L148


143           __cpuid(0x15, a, b, c, d);  
...
146           /* EBX : TSC/Crystal ratio, ECX : Crystal Hz */
147           if (b && c)
148               return c * (b / a);

On one machine, line 143 returns a 10 b 23 c 1000000000 d 0,
the division (b / a) returns 2 hence leading to
an incorrect value (2 GHz instead of 2.3 GHz)


The trivial fix is to replace line 148 with

    return (uint64_t)c * b / a;

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[DPDK/core Bug 1869] incorrect get_tsc_freq_arch() due to integer truncation

[bugzilla]

http://bugs.dpdk.org/show_bug.cgi?id=1869

Thomas Monjalon (thomas@monjalon.net) changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Thomas Monjalon (thomas@monjalon.net) ---
Resolved in http://git.dpdk.org/dpdk/commit/?id=a17499cf33

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