Add a comments to clarify about the usage of cpumask_intersects(). Moreover, update scx_select_cpu_dfl() description clarifying that the final step of the idle selection logic involves searching for any idle CPU in the system that the task can use. Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx> --- kernel/sched/ext_idle.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c index dedd39febc88..4952e2793304 100644 --- a/kernel/sched/ext_idle.c +++ b/kernel/sched/ext_idle.c @@ -52,6 +52,10 @@ static bool test_and_clear_cpu_idle(int cpu) * scx_pick_idle_cpu() can get caught in an infinite loop as * @cpu is never cleared from idle_masks.smt. Ensure that @cpu * is eventually cleared. + * + * NOTE: Use cpumask_intersects() and cpumask_test_cpu() to + * reduce memory writes, which may help alleviate cache + * coherence pressure. */ if (cpumask_intersects(smt, idle_masks.smt)) cpumask_andnot(idle_masks.smt, idle_masks.smt, smt); @@ -280,6 +284,8 @@ static void update_selcpu_topology(void) * 4. Pick a CPU within the same NUMA node, if enabled: * - choose a CPU from the same NUMA node to reduce memory access latency. * + * 5. Pick any idle CPU usable by the task. + * * Step 3 and 4 are performed only if the system has, respectively, multiple * LLC domains / multiple NUMA nodes (see scx_selcpu_topo_llc and * scx_selcpu_topo_numa). -- 2.47.1
