Re: [PATCH v2 2/2] x86/delay: Introduce TPAUSE delay

[Thomas Gleixner]

Andy Lutomirski <luto@xxxxxxxxxx> writes:
> On Thu, Mar 19, 2020 at 9:13 PM Kyung Min Park <kyung.min.park@xxxxxxxxx> wrote:
>>  void use_tsc_delay(void)
>>  {
>> -       if (delay_fn == delay_loop)
>> +       if (static_cpu_has(X86_FEATURE_WAITPKG)) {
>> +               delay_halt_fn = delay_halt_tpause;
>> +               delay_fn = delay_halt;
>> +       } else if (delay_fn == delay_loop) {
>>                 delay_fn = delay_tsc;
>> +       }
>>  }
>
> This is an odd way to dispatch: you're using static_cpu_has(), but
> you're using it once to populate a function pointer.  Why not just put
> the static_cpu_has() directly into delay_halt() and open-code the
> three variants?

Two: mwaitx and tpause.

> That will also make it a lot easier to understand the oddity with
> start and cycles.

Indeed. That makes sense. Should have thought about it :)

Thanks,

        tglx