linux-kernel - Re: [PATCH 2/2] x86/idle: use dynamic halt poll

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Date:   Fri, 23 Jun 2017 12:04:40 +0800
From:   Yang Zhang <yang.zhang.wz@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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Subject: Re: [PATCH 2/2] x86/idle: use dynamic halt poll

On 2017/6/22 22:32, Thomas Gleixner wrote:
> On Thu, 22 Jun 2017, root wrote:
>> @@ -962,6 +962,7 @@ __visible void __irq_entry smp_apic_timer_interrupt(struct pt_regs *regs)
>>  	 * interrupt lock, which is the WrongThing (tm) to do.
>>  	 */
>>  	entering_ack_irq();
>> +	check_poll();
>
> No way, that we sprinkle this function into every interrupt hotpath. There
> are enough genuine ways to do that w/o touching a gazillion of files.

I will find a more correct place to call this function.

>
>>  #ifdef CONFIG_HYPERVISOR_GUEST
>> +static unsigned int grow_poll_ns(unsigned int old, unsigned int grow,
>> +				      unsigned int max)
>> +{
>> +	unsigned int val;
>> +
>> +	/* 10us as base poll duration */
>> +	if (old == 0 && grow)
>> +		return 10000;
>> +
>> +	val = old * grow;
>> +	if (val > max)
>> +		val = max;
>> +
>> +	return val;
>> +}
>> +
>> +static unsigned int shrink_poll_ns(unsigned int old, unsigned int shrink)
>> +{
>> +	if (shrink == 0)
>> +		return 0;
>> +
>> +	return old / shrink;
>> +}
>> +
>> +void check_poll(void)
>> +{
>> +	unsigned int val, poll_duration;
>> +	unsigned long begin_ns, now_ns;
>> +
>> +	if (!poll_threshold_ns)
>> +		return;
>
> If at all then this needs to be a static key based decision.

Sure, will do it.

>
>> +
>> +	begin_ns = this_cpu_read(poll_begin_ns);
>> +	/* Not from halt state */
>> +	if (!begin_ns)
>> +		return;
>
> If you integrate this stuff into the proper place, then the whole mess goes
> away. We really do not need another facility to track idle state. We have
> enough already, really.

Agree, I will check current code to find a more proper way to do the check.

>
> Thanks,
>
> 	tglx
>


-- 
Yang
Alibaba Cloud Computing