Re: [Xen-devel] [PATCH] credit: track residual from divisions done during accounting

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.02.13 at 18:26, Dario Faggioli <dario.faggioli@xxxxxxxxxx> wrote:
> On Mon, 2013-02-18 at 12:37 +0000, Jan Beulich wrote:
>> --- a/xen/common/sched_credit.c
>> +++ b/xen/common/sched_credit.c
>>
>> @@ -242,6 +244,7 @@ __runq_remove(struct csched_vcpu *svc)
>>  static void burn_credits(struct csched_vcpu *svc, s_time_t now)
>>  {
>>      s_time_t delta;
>> +    uint64_t val;
>>      unsigned int credits;
>>  
>>      /* Assert svc is current */
>> @@ -250,7 +253,10 @@ static void burn_credits(struct csched_v
>>      if ( (delta = now - svc->start_time) <= 0 )
>>          return;
>>  
>> -    credits = (delta*CSCHED_CREDITS_PER_MSEC + MILLISECS(1)/2) / 
>> MILLISECS(1);
>> +    val = delta * CSCHED_CREDITS_PER_MSEC + svc->residual;
>> +    svc->residual = do_div(val, MILLISECS(1));
>> +    credits = val;
>> +    ASSERT(credits == val);
> 
> I may be missing something, but how can the assert ever be false, given
> the assignment right before it?

val being wider than credit, this checks that there was no truncation.

Jan


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