Messages in this thread | | | Date | Mon, 13 Feb 2017 12:12:57 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/2] sched/deadline: Throttle a constrained deadline task activated after the deadline |
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On Sat, Feb 11, 2017 at 08:15:26AM +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. >
Made that a "Reviewed-by:" tag in your name again.
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