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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2025-11-12 at 12:21 +0100, Peter Zijlstra wrote: > On Wed, Nov 12, 2025 at 04:39:43PM +0530, Shrikanth Hegde wrote: > >=20 > >=20 >=20 > > > So perhaps this is the better option -- or did I overlook something w= ith > > > should_we_balance? It doesn't look like that will make a different > > > decision on the retry. > > >=20 > >=20 > > I think in newidle balance, these checks are there in swb to bail of lo= ad balance. > > redo logic catches it right? >=20 > Urgh, my brain still thinks we're not serializing on newidle. Perhaps I > should make this 2 patches, one moving the serializing and one adding it > to newidle. >=20 > > env->dst_rq lock is taken only in attach_tasks, meanwhile, if the wakeu= p happened, > > pending would be set. is irq enabled or remote CPU can set ttwu_pending= on this rq? > >=20 > > if (env->idle =3D=3D CPU_NEWLY_IDLE) { > > if (env->dst_rq->nr_running > 0 || env->dst_rq->ttwu_pe= nding) > > return 0; > > return 1; > > } >=20 > Right, that could get tickled. How about something like the following on top of v4 patch? This will avoid releasing the lock and take care of the NEWLY_IDLE case. Tim diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 43c5ec039633..26179f4b77f6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11772,14 +11772,13 @@ static int sched_balance_rq(int this_cpu, struct = rq *this_rq, .fbq_type =3D all, .tasks =3D LIST_HEAD_INIT(env.tasks), }; - bool need_unlock; + bool need_unlock =3D false; =20 cpumask_and(cpus, sched_domain_span(sd), cpu_active_mask); =20 schedstat_inc(sd->lb_count[idle]); =20 redo: - need_unlock =3D false; if (!should_we_balance(&env)) { *continue_balancing =3D 0; goto out_balanced; @@ -11916,9 +11915,9 @@ static int sched_balance_rq(int this_cpu, struct rq= *this_rq, if (!cpumask_subset(cpus, env.dst_grpmask)) { env.loop =3D 0; env.loop_break =3D SCHED_NR_MIGRATE_BREAK; - if (need_unlock) - atomic_set_release(&sched_balance_running, 0); - + if (env->idle =3D=3D CPU_NEWLY_IDLE && + (env->dst_running > 0 || env->dst_rq->ttwu_pending)) + goto out; goto redo; } goto out_all_pinned;