From: Rik van Riel <riel@xxxxxxxxxx>
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@xxxxxxxxxxxxx>
Cc: Clark Williams <williams@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Luiz Capitulino <lcapitulino@xxxxxxxxxx>
Cc: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Cc: cgroups@xxxxxxxxxxxxxxx
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Tested-by: David Rientjes <rientjes@xxxxxxxxxx>
---
kernel/cpuset.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 1d1fe9361d29..b544e5229d99 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -625,6 +625,7 @@ 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 */
@@ -634,6 +635,10 @@ 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;
@@ -646,7 +651,8 @@ 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;
}
@@ -669,7 +675,8 @@ 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))
@@ -751,6 +758,7 @@ 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);
@@ -763,6 +771,7 @@ static int generate_sched_domains(cpumask_var_t **domains,
BUG_ON(nslot != ndoms);
done:
+ free_cpumask_var(non_isolated_cpus);
kfree(csa);
/*
--
2.1.0
--
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