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scx_rustland: evaluate the proper vruntime delta

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The forumla used to evaluate the weighted time delta is not correct,
it's not considering the weight as a percentage. Fix this by using the
proper formula.

Moreover, take into account also the task weight when evaluating the
maximum time delta to account in vruntime and make sure that we never
charge a task more than slice_ns.

This helps to prevent starvation of low priority tasks.

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
This commit is contained in:
Andrea Righi 2024-01-01 19:26:49 +01:00
parent 90e92ace2d
commit 2900b208fe
1 changed files with 2 additions and 3 deletions
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5
scheds/rust/scx_rustland/src/main.rs
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@ -355,11 +355,10 @@ impl<'a> Scheduler<'a> {
) {
// Add cputime delta normalized by weight to the vruntime (if delta > 0).
if sum_exec_runtime > task_info.sum_exec_runtime {
let mut delta = sum_exec_runtime - task_info.sum_exec_runtime;
let delta = (sum_exec_runtime - task_info.sum_exec_runtime) * 100 / weight;
// Never account more than max_slice_ns. This helps to prevent starving a task for too
// long in the scheduler task pool.
delta = delta.min(max_slice_ns);
task_info.vruntime += delta / weight;
task_info.vruntime += delta.min(max_slice_ns);
}
// Make sure vruntime is moving forward (> current minimum).
task_info.vruntime = task_info.vruntime.max(min_vruntime);