Re: [PATCH] credi2-ratelimit: Implement rate limit for credit2 scheduler

[George Dunlap <george.dunlap@citrix.com>]

On 13/07/16 09:53, Dario Faggioli wrote:
>> @@ -1675,9 +1711,19 @@ csched2_runtime(const struct scheduler *ops,
>> int cpu, struct csched2_vcpu *snext
>>       * 1) Run until snext's credit will be 0
>>       * 2) But if someone is waiting, run until snext's credit is
>> equal
>>       * to his
>> -     * 3) But never run longer than MAX_TIMER or shorter than
>> MIN_TIMER.
>> +     * 3) But never run longer than MAX_TIMER or shorter than
>> MIN_TIMER
>> +     * or your the ratelimit time.
>>       */
>>
>> +    /* Calculate mintime */
>> +    min_time = CSCHED2_MIN_TIMER;
>> +    if ( prv->ratelimit_us ) {
>> +        s_time_t ratelimit_min = snext->vcpu-
>>> runstate.state_entry_time +
>> +            MICROSECS(prv->ratelimit_us) - now;
>>
> Here snext can indeed be someone which was running already (e.g., we're
> choosing current again), in which case runstate.state_entry-time-now
> would indeed tell us how long it's actually been running, and the
> formula (coupled with the if below) is correct.
> 
> But it also can be someone which is runnable (e.g., we're choosing
> someone from the runqueue and preempting current), in which case
> runstate.state_entry_time tells when it became runnable, and
> state_entry_time-now is how long it's been runnable, which is not what
> we want here.
> 
> In think, in such a case, we want ratelimit_min to just be equal to
> prv->ratelimit_us. So, maybe, something like this:
> 
>  /* Caluclate mintime */
>  min_time = CSCHED2_MIN_TIMER;
>  if ( prv->ratelimit_us )
>  {
>      s_time_t ratelimit_min = prv->ratelimit_us;
>      if ( snext->vcpu->is_running )     // XXX or is it better snext == curr_on_cpu(cpu)
>          ratelimit_min = snext->vcpu->runstate.state_entry_time +
>                          MICROSECS(prv->ratelimit_us) - now;
>      if ( ratelimit_min > min_time )
>          min_time = ratelimit_min;
>  }

+1

 -George

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