Commit 47b8ea71 authored by Rik van Riel's avatar Rik van Riel Committed by Tejun Heo

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 <>
Cc: Clark Williams <>
Cc: Li Zefan <>
Cc: Ingo Molnar <>
Cc: Luiz Capitulino <>
Cc: Mike Galbraith <>
Signed-off-by: default avatarRik van Riel <>
Tested-by: default avatarDavid Rientjes <>
Acked-by: default avatarPeter Zijlstra (Intel) <>
Acked-by: default avatarDavid Rientjes <>
Acked-by: default avatarZefan Li <>
Signed-off-by: default avatarTejun Heo <>
parent 3fa0818b
......@@ -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,
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) &&
cpumask_intersects(cp->cpus_allowed, non_isolated_cpus)))
if (is_sched_load_balance(cp))
......@@ -748,6 +755,7 @@ restart:
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 @@ restart:
BUG_ON(nslot != ndoms);
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