[1/2] x86/idle: add halt poll for halt idle

[Yang Zhang <yang.zhang.wz@gmail.com>]

On 2017/6/22 22:23, Thomas Gleixner wrote:
> On Thu, 22 Jun 2017, root wrote:
>> --- a/arch/x86/kernel/process.c
>> +++ b/arch/x86/kernel/process.c
>> @@ -39,6 +39,10 @@
>>  #include <asm/desc.h>
>>  #include <asm/prctl.h>
>>
>> +#ifdef CONFIG_HYPERVISOR_GUEST
>> +unsigned long poll_threshold_ns;
>> +#endif
>> +
>>  /*
>>   * per-CPU TSS segments. Threads are completely 'soft' on Linux,
>>   * no more per-task TSS's. The TSS size is kept cacheline-aligned
>> @@ -313,6 +317,23 @@ static inline void play_dead(void)
>>  }
>>  #endif
>>
>> +#ifdef CONFIG_HYPERVISOR_GUEST
>> +void arch_cpu_idle_poll(void)
>> +{
>> +	ktime_t start, cur, stop;
>> +
>> +	if (poll_threshold_ns) {
>> +		start = cur = ktime_get();
>> +		stop = ktime_add_ns(ktime_get(), poll_threshold_ns);
>> +		do {
>> +			if (need_resched())
>> +				break;
>> +			cur = ktime_get();
>> +		} while (ktime_before(cur, stop));
>> +	}
>> +}
>> +#endif
>
> Aside of the whole approach being debatable, what's the reason to make this
> depend on CONFIG_HYPERVISOR_GUEST and to move it into x86. If that
> mechanism is worthwhile then it should go into the generic code and not
> into x86. There is absolutely nothing x86 specific in that patch.
>
> Also the CONFIG_HYPERVISOR_GUEST dependency is silly. Distro kernels ship
> with CONFIG_HYPERVISOR_GUEST=y so this also gets into affect on bare metal.

You are right. As Paolo suggested, i will integrate it with 
paravalization code.

>
> Thanks,
>
> 	tglx
>