On Mon, 7 Nov 2016 09:17:55 +0100 Daniel Bristot de Oliveira <bris...@redhat.com> wrote:
> The rt throttling mechanism prevents the starvation of non-real-time > tasks by CPU intensive real-time tasks. In terms of percentage, > the default behavior allows real-time tasks to run up to 95% of a > given period, leaving the other 5% of the period for non-real-time > tasks. In the absence of non-rt tasks, the system goes idle for 5% > of the period. > > Although this behavior works fine for the purpose of avoiding > bad real-time tasks that can hang the system, some greed users > want to allow the real-time task to continue running in the absence > of non-real-time tasks starving. In other words, they do not want to > see the system going idle. > > This patch implements the RT_RUNTIME_GREED scheduler feature for greedy > users (TM). When enabled, this feature will check if non-rt tasks are > starving before throttling the real-time task. If the real-time task > becomes throttled, it will be unthrottled as soon as the system goes > idle, or when the next period starts, whichever comes first. > > This feature is enabled with the following command: > # echo RT_RUNTIME_GREED > /sys/kernel/debug/sched_features > I'm still reviewing the patch, but I have to wonder why bother with making it a scheduler feature? The SCHED_FIFO definition allows a fifo thread to starve others because a fifo task will run until it yields. Throttling was added as a safety valve to allow starved SCHED_OTHER tasks to get some cpu time. Adding this unconditionally gets us a safety valve for throttling a badly written fifo task, but allows the fifo task to continue to consume cpu cycles if it's not starving anyone. Or am I missing something that's blazingly obvious? Clark
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