Commit 02f034dc authored by Andrea Righi's avatar Andrea Righi Committed by Tejun Heo
Browse files

sched_ext: idle: clarify comments 



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.

Reviewed-by: default avatarYury Norov <yury.norov@gmail.com>
Signed-off-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 9cf9acee

kernel/sched/ext.c

+6 −0
Original line number Diff line number Diff line
@@ -3180,6 +3180,10 @@ 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);
@@ -3408,6 +3412,8 @@ 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).