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Commit 47b8ea71 authored by Rik van Riel's avatar Rik van Riel Committed by Tejun Heo
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cpusets, isolcpus: exclude isolcpus from load balancing in cpusets 



Ensure that cpus specified with the isolcpus= boot commandline
option stay outside of the load balancing in the kernel scheduler.

Operations like load balancing can introduce unwanted latencies,
which is exactly what the isolcpus= commandline is there to prevent.

Previously, simply creating a new cpuset, without even touching the
cpuset.cpus field inside the new cpuset, would undo the effects of
isolcpus=, by creating a scheduler domain spanning the whole system,
and setting up load balancing inside that domain. The cpuset root
cpuset.cpus file is read-only, so there was not even a way to undo
that effect.

This does not impact the majority of cpusets users, since isolcpus=
is a fairly specialized feature used for realtime purposes.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Clark Williams <williams@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: cgroups@vger.kernel.org
Signed-off-by: default avatarRik van Riel <riel@redhat.com>
Tested-by: default avatarDavid Rientjes <rientjes@google.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
Acked-by: default avatarZefan Li <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 3fa0818b

kernel/cpuset.c

+11 −2
Original line number Diff line number Diff line
@@ -622,6 +622,7 @@ static int generate_sched_domains(cpumask_var_t **domains, 
	int csn;		/* how many cpuset ptrs in csa so far */

	int i, j, k;		/* indices for partition finding loops */

	cpumask_var_t *doms;	/* resulting partition; i.e. sched domains */

	cpumask_var_t non_isolated_cpus;  /* load balanced CPUs */

	struct sched_domain_attr *dattr;  /* attributes for custom domains */

	int ndoms = 0;		/* number of sched domains in result */

	int nslot;		/* next empty doms[] struct cpumask slot */
@@ -631,6 +632,10 @@ static int generate_sched_domains(cpumask_var_t **domains, 
	dattr = NULL;

	csa = NULL;



	if (!alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL))

		goto done;

	cpumask_andnot(non_isolated_cpus, cpu_possible_mask, cpu_isolated_map);



	/* Special case for the 99% of systems with one, full, sched domain */

	if (is_sched_load_balance(&top_cpuset)) {

		ndoms = 1;
@@ -643,7 +648,8 @@ static int generate_sched_domains(cpumask_var_t **domains, 
			*dattr = SD_ATTR_INIT;

			update_domain_attr_tree(dattr, &top_cpuset);

		}

		cpumask_copy(doms[0], top_cpuset.effective_cpus);

		cpumask_and(doms[0], top_cpuset.effective_cpus,

				     non_isolated_cpus);



		goto done;

	}
@@ -666,7 +672,8 @@ static int generate_sched_domains(cpumask_var_t **domains, 
		 * the corresponding sched domain.

		 */

		if (!cpumask_empty(cp->cpus_allowed) &&

		    !is_sched_load_balance(cp))

		    !(is_sched_load_balance(cp) &&

		      cpumask_intersects(cp->cpus_allowed, non_isolated_cpus)))

			continue;



		if (is_sched_load_balance(cp))
@@ -748,6 +755,7 @@ static int generate_sched_domains(cpumask_var_t **domains, 


			if (apn == b->pn) {

				cpumask_or(dp, dp, b->effective_cpus);

				cpumask_and(dp, dp, non_isolated_cpus);

				if (dattr)

					update_domain_attr_tree(dattr + nslot, b);
@@ -760,6 +768,7 @@ static int generate_sched_domains(cpumask_var_t **domains, 
	BUG_ON(nslot != ndoms);



done:

	free_cpumask_var(non_isolated_cpus);

	kfree(csa);



	/*