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authorJohannes Weiner <hannes@cmpxchg.org>2018-11-30 14:09:58 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-11-30 14:56:14 -0800
commite0c274472d5d27f277af722e017525e0b33784cd (patch)
treebbc5a80c7a61acf0747c62e78b741043561311d4 /kernel/sched/psi.c
parentdbd4af54745fc0c805217693c807a3928b2d408b (diff)
downloadlinux-e0c274472d5d27f277af722e017525e0b33784cd.tar.bz2
psi: make disabling/enabling easier for vendor kernels
Mel Gorman reports a hackbench regression with psi that would prohibit shipping the suse kernel with it default-enabled, but he'd still like users to be able to opt in at little to no cost to others. With the current combination of CONFIG_PSI and the psi_disabled bool set from the commandline, this is a challenge. Do the following things to make it easier: 1. Add a config option CONFIG_PSI_DEFAULT_DISABLED that allows distros to enable CONFIG_PSI in their kernel but leave the feature disabled unless a user requests it at boot-time. To avoid double negatives, rename psi_disabled= to psi=. 2. Make psi_disabled a static branch to eliminate any branch costs when the feature is disabled. In terms of numbers before and after this patch, Mel says: : The following is a comparision using CONFIG_PSI=n as a baseline against : your patch and a vanilla kernel : : 4.20.0-rc4 4.20.0-rc4 4.20.0-rc4 : kconfigdisable-v1r1 vanilla psidisable-v1r1 : Amean 1 1.3100 ( 0.00%) 1.3923 ( -6.28%) 1.3427 ( -2.49%) : Amean 3 3.8860 ( 0.00%) 4.1230 * -6.10%* 3.8860 ( -0.00%) : Amean 5 6.8847 ( 0.00%) 8.0390 * -16.77%* 6.7727 ( 1.63%) : Amean 7 9.9310 ( 0.00%) 10.8367 * -9.12%* 9.9910 ( -0.60%) : Amean 12 16.6577 ( 0.00%) 18.2363 * -9.48%* 17.1083 ( -2.71%) : Amean 18 26.5133 ( 0.00%) 27.8833 * -5.17%* 25.7663 ( 2.82%) : Amean 24 34.3003 ( 0.00%) 34.6830 ( -1.12%) 32.0450 ( 6.58%) : Amean 30 40.0063 ( 0.00%) 40.5800 ( -1.43%) 41.5087 ( -3.76%) : Amean 32 40.1407 ( 0.00%) 41.2273 ( -2.71%) 39.9417 ( 0.50%) : : It's showing that the vanilla kernel takes a hit (as the bisection : indicated it would) and that disabling PSI by default is reasonably : close in terms of performance for this particular workload on this : particular machine so; Link: http://lkml.kernel.org/r/20181127165329.GA29728@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Tested-by: Mel Gorman <mgorman@techsingularity.net> Reported-by: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sched/psi.c')
-rw-r--r--kernel/sched/psi.c30
1 files changed, 21 insertions, 9 deletions
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 3d7355d7c3e3..fe24de3fbc93 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -136,8 +136,18 @@
static int psi_bug __read_mostly;
-bool psi_disabled __read_mostly;
-core_param(psi_disabled, psi_disabled, bool, 0644);
+DEFINE_STATIC_KEY_FALSE(psi_disabled);
+
+#ifdef CONFIG_PSI_DEFAULT_DISABLED
+bool psi_enable;
+#else
+bool psi_enable = true;
+#endif
+static int __init setup_psi(char *str)
+{
+ return kstrtobool(str, &psi_enable) == 0;
+}
+__setup("psi=", setup_psi);
/* Running averages - we need to be higher-res than loadavg */
#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
@@ -169,8 +179,10 @@ static void group_init(struct psi_group *group)
void __init psi_init(void)
{
- if (psi_disabled)
+ if (!psi_enable) {
+ static_branch_enable(&psi_disabled);
return;
+ }
psi_period = jiffies_to_nsecs(PSI_FREQ);
group_init(&psi_system);
@@ -549,7 +561,7 @@ void psi_memstall_enter(unsigned long *flags)
struct rq_flags rf;
struct rq *rq;
- if (psi_disabled)
+ if (static_branch_likely(&psi_disabled))
return;
*flags = current->flags & PF_MEMSTALL;
@@ -579,7 +591,7 @@ void psi_memstall_leave(unsigned long *flags)
struct rq_flags rf;
struct rq *rq;
- if (psi_disabled)
+ if (static_branch_likely(&psi_disabled))
return;
if (*flags)
@@ -600,7 +612,7 @@ void psi_memstall_leave(unsigned long *flags)
#ifdef CONFIG_CGROUPS
int psi_cgroup_alloc(struct cgroup *cgroup)
{
- if (psi_disabled)
+ if (static_branch_likely(&psi_disabled))
return 0;
cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu);
@@ -612,7 +624,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
void psi_cgroup_free(struct cgroup *cgroup)
{
- if (psi_disabled)
+ if (static_branch_likely(&psi_disabled))
return;
cancel_delayed_work_sync(&cgroup->psi.clock_work);
@@ -637,7 +649,7 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
struct rq_flags rf;
struct rq *rq;
- if (psi_disabled) {
+ if (static_branch_likely(&psi_disabled)) {
/*
* Lame to do this here, but the scheduler cannot be locked
* from the outside, so we move cgroups from inside sched/.
@@ -673,7 +685,7 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
{
int full;
- if (psi_disabled)
+ if (static_branch_likely(&psi_disabled))
return -EOPNOTSUPP;
update_stats(group);