Re: [PATCH v9]xen: sched: convert RTDS from time to event driven model

["Chen, Tianyang" <tiche@seas.upenn.edu>]

On 03/15/2016 11:11 PM, Meng Xu wrote:
>> +
>>   /*
>>    * Flags
>>    */
>> @@ -115,6 +118,18 @@
>>   #define RTDS_delayed_runq_add (1<<__RTDS_delayed_runq_add)
>>
>>   /*
>> + * The replenishment timer handler needs to check this bit
>> + * to know where a replenished vcpu was, when deciding which
>> + * vcpu should tickle.
>> + * A replenished vcpu should tickle if it was moved from the
>> + * depleted queue to the run queue.
>> + * + Set in burn_budget() if a vcpu has zero budget left.
>> + * + Cleared and checked in the repenishment handler.
>
> It seems you have an extra + here...
> Need to be removed.
>
> My bad, I didn't spot it out in last patch... :-(
>

You mean before "Cleared"? For __RTDS_scheduled there are '+' before 
'Cleared', 'Checked', 'Set'.

>> @@ -840,8 +991,6 @@ rt_schedule(const struct scheduler *ops, s_time_t now, bool_t tasklet_work_sched
>>       /* burn_budget would return for IDLE VCPU */
>>       burn_budget(ops, scurr, now);
>>
>> -    __repl_update(ops, now);
>> -
>>       if ( tasklet_work_scheduled )
>>       {
>>           trace_var(TRC_RTDS_SCHED_TASKLET, 1, 0,  NULL);
>> @@ -868,6 +1017,7 @@ rt_schedule(const struct scheduler *ops, s_time_t now, bool_t tasklet_work_sched
>>           set_bit(__RTDS_delayed_runq_add, &scurr->flags);
>>
>>       snext->last_start = now;
>> +    ret.time =  -1; /* if an idle vcpu is picked */
>>       if ( !is_idle_vcpu(snext->vcpu) )
>>       {
>>           if ( snext != scurr )
>> @@ -880,9 +1030,8 @@ rt_schedule(const struct scheduler *ops, s_time_t now, bool_t tasklet_work_sched
>>               snext->vcpu->processor = cpu;
>>               ret.migrated = 1;
>>           }
>> +        ret.time = snext->budget; /* invoke the scheduler next time */
>
> Ah, this is incorrect, although this is easy to fix.
>
> The ret.time is the relative time when the *budget enforcement* timer
> should be invoked.
> Since snext is not always full budget, it may have already consumed some budget.
>
> It should be
> ret.time = snext->cur_budget
>
> Isn't it? :-)
Good catch. This bug kinda ruins the fix for busy waiting.

Thanks,
Tianyang


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