Re: [dpdk-dev] [PATCH v2 3/3] app/testpmd: qualify profiling statistics on burst size

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 3/20/2020 6:13 AM, Jerin Jacob wrote:
> On Thu, Mar 19, 2020 at 7:21 PM Viacheslav Ovsiienko
> <viacheslavo@mellanox.com> wrote:
>>
>> The execution time of rx/tx burst routine depends on the burst size.
>> It would be meaningful to research this dependency, the patch
>> provides an extra profiling data per rx/tx burst size.
>>
>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> 
>> +#ifdef RTE_TEST_PMD_RECORD_CORE_CYCLES
>> +       if (!(fwdprof_flags & (nrx_tx ? RECORD_CORE_CYCLES_TX
>> +                                     : RECORD_CORE_CYCLES_RX)))
>> +               return;
>> +       for (nb_pkt = 0; nb_pkt < MAX_PKT_BURST; nb_pkt++) {
>> +               nb_burst = nrx_tx ? pbs->pkt_retry_spread[nb_pkt]
>> +                                 : pbs->pkt_burst_spread[nb_pkt];
>> +               if (nb_burst == 0)
>> +                       continue;
>> +               printf("  CPU cycles/%u packet burst=%u (total cycles="
>> +                      "%"PRIu64" / total %s bursts=%u)\n",
>> +                      (unsigned int)nb_pkt,
>> +                      (unsigned int)(pbs->pkt_ticks_spread[nb_pkt] / nb_burst),
>> +                      pbs->pkt_ticks_spread[nb_pkt],
>> +                      nrx_tx ? "TX" : "RX", nb_burst);
>> +       }
>> +#endif
> 
> 
> # Thanks for this feature, IMO, It worth to mention in release notes.
> 
> # I see a lot of code get added under RTE_TEST_PMD_RECORD_CORE_CYCLES.
> I agree that it should be under RTE_TEST_PMD_RECORD_CORE_CYCLES. Since
> this flag is not
> by default, there is a risk of compilation issue when this flag is get enabled.
> IMO, it is better to move to _if (0)_ semantics to enable
> - performance when compiler opt-out the code.
> - It forces the compiler to check the compilation errors irrespective
> of the RTE_TEST_PMD_RECORD_CORE_CYCLES state.
> 
> Something like below,
> 
> static __rte_always_inline int
> testpmd_has_stats_feature(void)
> {
> #ifdef RTE_TEST_PMD_RECORD_CORE_CYCLES
>         return RTE_TEST_PMD_RECORD_CORE_CYCLES ;
> #else
>         return 0;
> #endif
> }
> 
> 
> if (testpmd_has_stats_feature()) {
> 
> }
> 

Hi Jerin,

In this usage, compiler will removed the "if (0) { }" block, right?
I think this is good idea, we can use it other places too, including this one.