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? If we go this way, then we can remove the while loop from replenish_dl_entity(), and change it in WARN_ON(dl_se->runtime <= -pi_se->dl_runtime); WARN_ON(dl_se->runtime > 0); dl_se->deadline += pi_se->dl_period; dl_se->runtime += pi_se->dl_runtime; or something similar. Luca
