On Wed, Aug 09, 2017 at 03:19:02PM +0000, Ofer Levi(SW) wrote:
> I appreciate your effort and detailed reply, however I'm still experiencing
> performance hit at
> partition_sched_domains(). It seems the issue is due to the large magnitude
> of cpus.
> I used he suggested method 2, patched in the diffs and used the command line
> switch isolcpus to
> kill load-balancing.
> It did save few hundredth of a sec per cpu. When I limited number of
> available cpus
> (using present and possible cpus ) to 48, it did reduced dramatically this
> function execution time:
>
> With 4K available cpus :
> [ 48.890000] ## CPU16 LIVE ##: Executing Code...
> [ 48.910000] partition_sched_domains start
> [ 49.360000] partition_sched_domains end
>
> With 48 available cpus:
> [ 36.950000] ## CPU16 LIVE ##: Executing Code...
> [ 36.950000] partition_sched_domains start
> [ 36.960000] partition_sched_domains end
>
> Note that I currently use kernel version: 4.8.0.17.0600.00.0000, if this has
> any influence.
> Would appreciate your thoughts.
>
Does something like this cure things? It seems we're doing a
possible_cpus iteration for sysctl cruft, and that will most certainly
hurt on your little toy :-)
Not sure what the more generic solution to that would be, but the below
avoids it for isolcpus.
---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -85,6 +85,7 @@ int sysctl_sched_rt_runtime = 950000;
/* CPUs with isolated domains */
cpumask_var_t cpu_isolated_map;
+cpumask_var_t non_isolated_cpus;
/*
* __task_rq_lock - lock the rq @p resides on.
@@ -5685,8 +5686,6 @@ static inline void sched_init_smt(void)
void __init sched_init_smp(void)
{
- cpumask_var_t non_isolated_cpus;
-
alloc_cpumask_var(&non_isolated_cpus, GFP_KERNEL);
sched_init_numa();
@@ -5697,17 +5696,17 @@ void __init sched_init_smp(void)
* happen.
*/
mutex_lock(&sched_domains_mutex);
- sched_init_domains(cpu_active_mask);
cpumask_andnot(non_isolated_cpus, cpu_possible_mask, cpu_isolated_map);
if (cpumask_empty(non_isolated_cpus))
cpumask_set_cpu(smp_processor_id(), non_isolated_cpus);
+
+ sched_init_domains(cpu_active_mask);
mutex_unlock(&sched_domains_mutex);
/* Move init over to a non-isolated CPU */
if (set_cpus_allowed_ptr(current, non_isolated_cpus) < 0)
BUG();
sched_init_granularity();
- free_cpumask_var(non_isolated_cpus);
init_sched_rt_class();
init_sched_dl_class();
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -327,6 +327,8 @@ static struct ctl_table *sd_alloc_ctl_cp
return table;
}
+extern cpumask_var_t non_isolated_cpus;
+
static struct ctl_table_header *sd_sysctl_header;
void register_sched_domain_sysctl(void)
{
@@ -340,7 +342,7 @@ void register_sched_domain_sysctl(void)
if (entry == NULL)
return;
- for_each_possible_cpu(i) {
+ for_each_cpu(i, non_isolated_cpus) {
snprintf(buf, 32, "cpu%d", i);
entry->procname = kstrdup(buf, GFP_KERNEL);
entry->mode = 0555;
