Messages in this thread | | | Date | Wed, 22 May 2013 10:16:01 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH RFC] sched/rt: preserve global runtime/period ratio in do_balance_runtime() |
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On Tue, May 21, 2013 at 02:30:09PM -0700, Peter Boonstoppel wrote: > RT throttling aims to prevent starvation of non-SCHED_FIFO threads > when a rogue RT thread is hogging the CPU. It does so by piggybacking > on the rt_bandwidth system and allocating at most rt_runtime per > rt_period to SCHED_FIFO tasks (e.g. 950ms out of every second, > allowing 'regular' tasks to run for at least 50ms every second). > > However, when multiple cores are available, rt_bandwidth allows cores > to borrow rt_runtime from one another. This means that a core with a > rogue RT thread, consuming 100% CPU cycles, can borrow enough runtime > from other cores to allow the RT thread to run continuously, with no > runtime for regular tasks on this core. > > Although regular tasks can get scheduled on other available cores > (which are guaranteed to have some non-RT runtime avaible, since they > just lent some RT time to us), tasks that are specifically affined to > a particular core may not be able to make progress (e.g. workqueues, > timer functions). This can break e.g. watchdog-like functionality that > is supposed to kill the rogue RT thread. > > This patch changes do_balance_runtime() in such a way that no core can > aquire (borrow) more runtime than the globally set rt_runtime / > rt_period ratio. This guarantees there will always be some non-RT > runtime available on every individual core. > > Signed-off-by: Peter Boonstoppel <pboonstoppel@nvidia.com>
I thought we already had a knob for that; RT_RUNTIME_SHARE. And as Mike said, we might consider flipping the default on that.
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