Messages in this thread | | | Subject | Re: [PATCH 2/2] sched/deadline: Throttle a constrained deadline task activated after the deadline | From | Mike Galbraith <> | Date | Sat, 11 Feb 2017 09:00:06 +0100 |
| |
On Sat, 2017-02-11 at 08:15 +0100, luca abeni wrote: > Hi Daniel, > > On Fri, 10 Feb 2017 20:48:11 +0100 > Daniel Bristot de Oliveira <bristot@redhat.com> wrote: > > > During the activation, CBS checks if it can reuse the current > > task's > > runtime and period. If the deadline of the task is in the past, CBS > > cannot use the runtime, and so it replenishes the task. This rule > > works fine for implicit deadline tasks (deadline == period), and > > the > > CBS was designed for implicit deadline tasks. However, a task with > > constrained deadline (deadine < period) might be awakened after the > > deadline, but before the next period. In this case, replenishing > > the > > task would allow it to run for runtime / deadline. As in this case > > deadline < period, CBS enables a task to run for more than the > > runtime/period. In a very load system, this can cause the domino > > effect, making other tasks to miss their deadlines. > > I think you are right: SCHED_DEADLINE implements the original CBS > algorithm here, but uses relative deadlines different from periods in > other places (while the original algorithm only considered relative > deadlines equal to periods). > An this mix is dangerous... I think your fix is correct, and cures a > real problem.
Both of these should be tagged for stable as well, or?
-Mike
| |