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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: Rik van Riel <riel@redhat.com>
Tested-by: David Rientjes <rientjes@google.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: David Rientjes <rientjes@google.com>
Acked-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Rik van Riel 2015-03-09 12:12:08 -04:00 committed by Tejun Heo
parent 3fa0818b3c
commit 47b8ea7186
1 changed files with 11 additions and 2 deletions
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13
kernel/cpuset.c
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@ -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 @@ 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);
done:
free_cpumask_var(non_isolated_cpus);
kfree(csa);
/*