Re: [PATCH 2/5] mc146818rtc: fix clock lost after scaling coalesced irq

[Xiao Guangrong <guangrong.xiao@gmail.com>]

On 05/03/2017 11:15 PM, Paolo Bonzini wrote:
> 
> 
> On 12/04/2017 11:51, guangrong.xiao@gmail.com wrote:
>> +            int current_irq_coalesced = s->irq_coalesced;
>> +
>> +            s->irq_coalesced = (current_irq_coalesced * s->period) / period;
>> +
>> +            /*
>> +             * calculate the lost clock after it is scaled which should be
>> +             * compensated in the next interrupt.
>> +             */
>> +            lost_clock += current_irq_coalesced * s->period -
>> +                            s->irq_coalesced * period;
> 
> This is:
> 
>     lost_clock = current_irq_coalesced * s->period -
> 	(current_irq_coalesced * s->period) / period * period;
> 
> i.e.
> 
>     /* When switching from a shorter to a longer period, scale down the
>      * missing ticks since we expect the OS handler to treat the delayed
>      * ticks as longer.  Any leftovers are put back into next_irq_clock.
>      *
>      * When switching to a shorter period, scale up the missing ticks
>      * since we expect the OS handler to treat the delayed ticks as
>      * shorter.
>      */
>     lost_clock = (s->irq_coalesced * s->period) % period;
>     s->irq_coalesced = (s->irq_coalesced * s->period) / period;
> 
> Is this correct?
> 

Yes, it is correct, it looks smarter, will apply it in the next version.

Thanks!