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scx_lavd: add a fastpath in ops.select_cpu() for a sharply pinned task

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If a task can be run only on a single cpu, we don't need to go through
all the steps in ops.select_cpu(). Instread, we simply check if a task
is still pinned on the prev_cpu and go.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-08-30 10:18:09 +09:00
parent b54fc202b8
commit a89a56dba4
1 changed files with 14 additions and 1 deletions
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15
scheds/rust/scx_lavd/src/bpf/main.bpf.c
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@ -1356,11 +1356,23 @@ static s32 pick_idle_cpu(struct task_struct *p, struct task_ctx *taskc,
struct bpf_cpumask *active, *ovrflw, *big, *little, *cpdom_mask_prev;
s32 cpu_id;
bpf_rcu_read_lock();
/*
* If a task can run only on a single CPU (e.g., per-CPU kworker), we
* simply check if a task is still pinned on the prev_cpu and go.
*/
if (p->nr_cpus_allowed == 1 &&
bpf_cpumask_test_cpu(prev_cpu, p->cpus_ptr)) {
if (scx_bpf_test_and_clear_cpu_idle(prev_cpu))
*is_idle = true;
cpu_id = prev_cpu;
goto out;
}
/*
* Prepare cpumaks.
*/
bpf_rcu_read_lock();
cpuc = get_cpu_ctx();
cpuc_prev = get_cpu_ctx_id(prev_cpu);
if (!cpuc || !cpuc_prev || !taskc) {
@ -1515,6 +1527,7 @@ start_any_mask:
*/
unlock_out:
bpf_rcu_read_unlock();
out:
return cpu_id;
}