On 18/10/18 13:08, luca abeni wrote: > On Thu, 18 Oct 2018 12:47:13 +0200 > Juri Lelli <[email protected]> wrote: > > > Hi, > > > > On 18/10/18 12:23, luca abeni wrote: > > > Hi Juri, > > > > > > On Thu, 18 Oct 2018 10:28:38 +0200 > > > Juri Lelli <[email protected]> wrote: > > > [...] > > > > struct sched_attr { > > > > .size = 0, > > > > .policy = 6, > > > > .flags = 0, > > > > .nice = 0, > > > > .priority = 0, > > > > .runtime = 0x9917, > > > > .deadline = 0xffff, > > > > .period = 0, > > > > } > > > > > > > > So, we seem to be correctly (in theory, see below) accepting the > > > > task. > > > > > > > > What seems to generate the problem here is that CONFIG_HZ=100 and > > > > reproducer task has "tiny" runtime (~40us) and deadline (~66us) > > > > parameters, combination that "bypasses" the enforcing mechanism > > > > (performed at each tick). > > > > > > Ok, so the task can execute for at most 1 tick before being > > > throttled... Which does not look too bad. > > > > > > I missed the original emails, but maybe the issue is that the task > > > blocks before the tick, and when it wakes up again something goes > > > wrong with the deadline and runtime assignment? (maybe because the > > > deadline is in the past?) > > > > No, the problem is that the task won't be throttled at all, because > > its replenishing instant is always way in the past when tick > > occurs. :-/ > > Ok, I see the issue now: the problem is that the "while (dl_se->runtime > <= 0)" loop is executed at replenishment time, but the deadline should > be postponed at enforcement time. > > I mean: in update_curr_dl() we do: > dl_se->runtime -= scaled_delta_exec; > if (dl_runtime_exceeded(dl_se) || dl_se->dl_yielded) { > ... > enqueue replenishment timer at dl_next_period(dl_se) > But dl_next_period() is based on a "wrong" deadline! > > > I think that inserting a > while (dl_se->runtime <= -pi_se->dl_runtime) { > dl_se->deadline += pi_se->dl_period; > dl_se->runtime += pi_se->dl_runtime; > } > immediately after "dl_se->runtime -= scaled_delta_exec;" would fix the > problem, no?
Mmm, I also thought of letting the task "pay back" its overrunning. But, doesn't this get us quite far from what one would expect. I mean, enforcement granularity will be way different from task period, no?
