Improve scx_rustland reliability #66
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Use SCX_ENQ_PREEMPT to dispatch the user-space scheduler. This can help to mitigate starvation in presence of many cpu hogs (way more than the amount of available CPUs) running in the system, by giving the scheduler more chances to drain the amount of tasks that may be starving in a waiting state. Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Instead of accounting (max_slice_ns / 2) to the vruntime of all the new tasks, add that to thier regular weighted time delta, as an additional penalty. This allows to distinguish new CPU intensive tasks vs new less CPU intensive tasks, and prioritize the latter over the former. Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
While bypassing the user-space scheduler can provide some benefits at reducing the scheduling overhead, doing so underneath the scheduler while it is actively taking decisions may disrupt its work and have a negative effect on the overall system performance. For this reason, activate the logic to bypass the user-space scheduler only when there is no pending work it. This change makes the scheduler much more reliable, for example on a 8-cores system it is really easy to trigger short lockups or even trigger the sched-ext watchdog that kicks out the scheduler, running the following stress test: $ stress-ng -c 128 With this change applied the system remains reasonably responsive and the scheduler is never disabled by the sched-ext watchdog. Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
htejun
approved these changes
Jan 4, 2024
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A small set of changes to improve scx_rustland reliability and make it more robust under heavy CPU load conditions.
Example (on a 8-cores system)
Before, this stress test could easily trigger short lockups or even trigger the sched-ext watchdog that would automatically disable the scheduler.
With this set of changes applied the system remains reasonably responsive and the scheduler is never disabled.