On Mon, 7 Nov 2016 21:33:02 +0100 Daniel Bristot de Oliveira <daniel@xxxxxxxxxx> wrote: > On 11/07/2016 09:16 PM, Steven Rostedt wrote: > > I'm confused? Are you saying that RR tasks don't get throttled in the > > current code? That sounds like a bug to me. > > If the RT_RUNTIME_SHARING is enabled, the CPU in which the RR tasks are > running (and pinned) will borrow RT runtime from another CPU, allowing > the RR tasks to run forever. For example: > > [root@kiron debug]# cat /proc/sched_debug | grep rt_runtime > .rt_runtime : 950.000000 > .rt_runtime : 950.000000 > .rt_runtime : 950.000000 > .rt_runtime : 950.000000 > [root@kiron debug]# echo RT_RUNTIME_SHARE > sched_features > [root@kiron debug]# taskset -c 2 chrt -r 5 /home/bristot/f & > [1] 23908 > [root@kiron debug]# taskset -c 2 chrt -r 5 /home/bristot/f & > [2] 23915 > [root@kiron debug]# cat /proc/sched_debug | grep rt_runtime > .rt_runtime : 900.000000 > .rt_runtime : 950.000000 > .rt_runtime : 1000.000000 > .rt_runtime : 950.000000 > > You see? the rt_runtime of the CPU 2 was borrowed time from CPU 0. > > It is not a BUG but a feature (no jokes haha). With RT_RUNTIME_SHARE, > the rt_runtime is such a global runtime. It works fine for tasks that > can migrate... but that is not the case for per-cpu kworkers. This still looks like a bug, or not the expected result. Perhaps we shouldn't share when tasks are pinned. It doesn't make sense. It's like pinning two deadline tasks to the same CPU and giving them 100% of that CPU and saying that it's really just 1/nr_cpus of usage, which would have the same effect. OK, it appears this is specific to RT_RUNTIME_SHARE which is what causes this strange behavior, and even more rational to make this a default option and perhaps even turn RT_RUNTIME_SHARE off by default. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
