Messages in this thread | | | Date | Wed, 11 Apr 2012 23:56:23 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH 08/16] sched: add period support for -deadline tasks. |
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On 04/11/2012 10:32 PM, Steven Rostedt wrote: > On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote: > >> @@ -293,7 +293,11 @@ static void replenish_dl_entity(struct sched_dl_entity *dl_se) >> * assigned (function returns true if it can). >> * >> * For this to hold, we must check if: >> - * runtime / (deadline - t)< dl_runtime / dl_deadline . >> + * runtime / (deadline - t)< dl_runtime / dl_period . >> + * >> + * Notice that the bandwidth check is done against the period. For >> + * task with deadline equal to period this is the same of using >> + * dl_deadline instead of dl_period in the equation above. > > First, it seems that the function returns true if: > > dl_runtime / dl_period< runtime / (deadline - t) >
Right, the comment is wrong! Just reverse the inequality as you did.
> > I'm a little confused by this. We are comparing the ratio of runtime > left and deadline left, to the ratio of total runtime to period. > > I'm actually confused by this premise anyway. What's the purpose of > comparing the ratio? If runtime< (deadline - t) wouldn't it not be able > to complete anyway? Or are we thinking that the runtime will be > interrupted proportionally by other tasks? >
We are actually applying one of the CBS rules. We want to be able to "slow down" a deadline task if it is going to exceed its reserved bandwidth. We are in fact checking here that the bandwidth this task will consume from t to its deadline is no more than its reserved one.
> > >> */ >> static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t) >> { >> @@ -312,7 +316,7 @@ static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t) >> * to the (absolute) deadline. Therefore, overflowing the u64 >> * type is very unlikely to occur in both cases. >> */ >> - left = dl_se->dl_deadline * dl_se->runtime; >> + left = dl_se->dl_period * dl_se->runtime; >> right = (dl_se->deadline - t) * dl_se->dl_runtime; >> >> return dl_time_before(right, left); > >
Thanks,
- Juri
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