Commit e0c27447 authored by Johannes Weiner's avatar Johannes Weiner Committed by Linus Torvalds

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.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Tested-by: default avatarMel Gorman <mgorman@techsingularity.net>
Reported-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent dbd4af54
......@@ -3505,6 +3505,10 @@
before loading.
See Documentation/blockdev/ramdisk.txt.
psi= [KNL] Enable or disable pressure stall information
tracking.
Format: <bool>
psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
probe for; one of (bare|imps|exps|lifebook|any).
psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
......
#ifndef _LINUX_PSI_H
#define _LINUX_PSI_H
#include <linux/jump_label.h>
#include <linux/psi_types.h>
#include <linux/sched.h>
......@@ -9,7 +10,7 @@ struct css_set;
#ifdef CONFIG_PSI
extern bool psi_disabled;
extern struct static_key_false psi_disabled;
void psi_init(void);
......
......@@ -509,6 +509,15 @@ config PSI
Say N if unsure.
config PSI_DEFAULT_DISABLED
bool "Require boot parameter to enable pressure stall information tracking"
default n
depends on PSI
help
If set, pressure stall information tracking will be disabled
per default but can be enabled through passing psi_enable=1
on the kernel commandline during boot.
endmenu # "CPU/Task time and stats accounting"
config CPU_ISOLATION
......
......@@ -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);
......
......@@ -66,7 +66,7 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup)
{
int clear = 0, set = TSK_RUNNING;
if (psi_disabled)
if (static_branch_likely(&psi_disabled))
return;
if (!wakeup || p->sched_psi_wake_requeue) {
......@@ -86,7 +86,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
{
int clear = TSK_RUNNING, set = 0;
if (psi_disabled)
if (static_branch_likely(&psi_disabled))
return;
if (!sleep) {
......@@ -102,7 +102,7 @@ static inline void psi_dequeue(struct task_struct *p, bool sleep)
static inline void psi_ttwu_dequeue(struct task_struct *p)
{
if (psi_disabled)
if (static_branch_likely(&psi_disabled))
return;
/*
* Is the task being migrated during a wakeup? Make sure to
......@@ -128,7 +128,7 @@ static inline void psi_ttwu_dequeue(struct task_struct *p)
static inline void psi_task_tick(struct rq *rq)
{
if (psi_disabled)
if (static_branch_likely(&psi_disabled))
return;
if (unlikely(rq->curr->flags & PF_MEMSTALL))
......
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