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Commit 3dc54b04 authored by Johannes Weiner's avatar Johannes Weiner Committed by Patrick Daly
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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: 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>
Change-Id: Idbf6ec163adcea17e8697b963e0ca2fe93cf2501
Git-commit: e0c274472d5d27f277af722e017525e0b33784cd
Git-repo: https://source.codeaurora.org/quic/la/kernel/msm-4.19


Signed-off-by: default avatarPatrick Daly <pdaly@codeaurora.org>
parent 88ec4749

Documentation/admin-guide/kernel-parameters.txt

+4 −0
Original line number Diff line number Diff line
@@ -3490,6 +3490,10 @@ 
			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

include/linux/psi.h

+2 −1
Original line number Diff line number Diff line 
#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);

init/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -523,6 +523,15 @@ 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

kernel/sched/psi.c

+21 −9
Original line number Diff line number Diff line
@@ -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);

kernel/sched/stats.h

+4 −4
Original line number Diff line number Diff line
@@ -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))