Re: [PATCH] migration/throttle: Make throttle slower at tail stage

[zhukeqian]

On 2020/2/14 20:28, Dr. David Alan Gilbert wrote:
> * Keqian Zhu (address@hidden) wrote:
>> At the tail stage of throttle, VM is very sensitive to
>> CPU percentage. We just throttle 30% of remaining CPU
>> when throttle is more than 80 percentage.
> 
> This is a bit unusual;  all of the rest of the throttling has no
> fixed constants; all values are set by parameters.
> 
> You've got the two, the '80' and the '0.3'
> 
> I thinkt he easy solution is to replace your parameter 'tailslow' by two
> new parameters; 'tailstart' and 'tailrate';  both defaulting to 100%.
> 
> Then you make it:
> 
>         if (cpu_throttle_now >= pct_tailstart) {
>             /* Eat some scale of CPU from remaining */
>             cpu_throttle_inc = ceil((100 - cpu_throttle_now) * pct_tailrate);
> 
> (with percentage scaling added).
> 
> Then setting 'tailstart' to 80 and 'tailrate' to 30 is equivalent to
> what you have, but means we have no magical constants in the code.
> 
Yes, this is a good suggestion. Though this patch is not the final idea,
I will apply it when throttle approach is decided.
> Dave
> 
> 
[...]
>> -- 
>> 2.19.1
>>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
> 
> 
> .
> 
Thanks,
Keqian