| Subject | Re: [PATCH 05/16] sched: SCHED_DEADLINE policy implementation. | From | Peter Zijlstra <> | Date | Mon, 23 Apr 2012 16:11:48 +0200 |
| |
On Fri, 2012-04-06 at 09:14 +0200, Juri Lelli wrote: > +static int start_dl_timer(struct sched_dl_entity *dl_se) > +{ > + struct dl_rq *dl_rq = dl_rq_of_se(dl_se); > + struct rq *rq = rq_of_dl_rq(dl_rq); > + ktime_t now, act; > + ktime_t soft, hard; > + unsigned long range; > + s64 delta; > + > + /* > + * We want the timer to fire at the deadline, but considering > + * that it is actually coming from rq->clock and not from > + * hrtimer's time base reading. > + */ > + act = ns_to_ktime(dl_se->deadline); > + now = hrtimer_cb_get_time(&dl_se->dl_timer); > + delta = ktime_to_ns(now) - rq->clock; > + act = ktime_add_ns(act, delta);
Right, this all is very sad.. but I guess we'll have to like live with it. The only other option is adding another timer base that tries to keep itself in sync with rq->clock but that all sounds very painful indeed.
Keeping up with rq->clock_task would be even more painful since it slows the clock down in random fashion making the timer fire early. Compensating that is going to be both fun and expensive.
> + /* > + * If the expiry time already passed, e.g., because the value > + * chosen as the deadline is too small, don't even try to > + * start the timer in the past! > + */ > + if (ktime_us_delta(act, now) < 0) > + return 0; > + > + hrtimer_set_expires(&dl_se->dl_timer, act); > + > + soft = hrtimer_get_softexpires(&dl_se->dl_timer); > + hard = hrtimer_get_expires(&dl_se->dl_timer); > + range = ktime_to_ns(ktime_sub(hard, soft)); > + __hrtimer_start_range_ns(&dl_se->dl_timer, soft, > + range, HRTIMER_MODE_ABS, 0); > + > + return hrtimer_active(&dl_se->dl_timer); > +}
/me reminds himself to make __hrtimer_start_range_ns() return -ETIME.
|