[PATCH 1/2] sched: Optimise task_mm_cid_work duration

[Gabriele Monaco <gmonaco@redhat.com>]

The current behaviour of task_mm_cid_work is to loop through all
possible CPUs twice to clean up old mm_cid remotely, this can be a waste
of resources especially on tasks with a CPU affinity.

This patch reduces the CPUs involved in the remote CID cleanup carried
on by task_mm_cid_work.

Using the mm_cidmask for the remote cleanup can considerably reduce the
function runtime in highly isolated environments, where each process has
affinity to a single core.  Likewise, in the worst case, the mask is
equivalent to all possible CPUs and we don't see any difference with the
current behaviour.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
---
 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 95e40895a519..57b50b5952fa 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10553,14 +10553,14 @@ static void task_mm_cid_work(struct callback_head *work)
 		return;
 	cidmask = mm_cidmask(mm);
 	/* Clear cids that were not recently used. */
-	for_each_possible_cpu(cpu)
+	for_each_cpu_from(cpu, cidmask)
 		sched_mm_cid_remote_clear_old(mm, cpu);
 	weight = cpumask_weight(cidmask);
 	/*
 	 * Clear cids that are greater or equal to the cidmask weight to
 	 * recompact it.
 	 */
-	for_each_possible_cpu(cpu)
+	for_each_cpu_from(cpu, cidmask)
 		sched_mm_cid_remote_clear_weight(mm, cpu, weight);
 }
 
-- 
2.47.0