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Message-ID: <20181127164617.GA29488@cmpxchg.org>
Date: Tue, 27 Nov 2018 11:46:17 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Mel Gorman <mgorman@...hsingularity.net>
Cc: Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org
Subject: Re: Hackbench pipes regression bisected to PSI
On Mon, Nov 26, 2018 at 11:29:26PM +0000, Mel Gorman wrote:
> 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;
>
> Tested-by: Mel Gorman <mgorman@...hsingularity.net>
Thanks for testing it. Let's add these results to the changelog:
---
>From 347b69a52d1ec7e71df1108cbc5703d6dd0616ba Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@...xchg.org>
Date: Mon, 26 Nov 2018 09:39:23 -0500
Subject: [PATCH] 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_ENABLED that allows distros
to enable CONFIG_PSI in their kernel, but leaving 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;
Tested-by: Mel Gorman <mgorman@...hsingularity.net>
Reported-by: Mel Gorman <mgorman@...hsingularity.net>
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
.../admin-guide/kernel-parameters.txt | 4 +++
include/linux/psi.h | 3 +-
init/Kconfig | 9 ++++++
kernel/sched/psi.c | 30 +++++++++++++------
kernel/sched/stats.h | 8 ++---
5 files changed, 40 insertions(+), 14 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 19f4423e70d9..8760a343c6d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3504,6 +3504,10 @@
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
diff --git a/include/linux/psi.h b/include/linux/psi.h
index 8e0725aac0aa..7006008d5b72 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -1,6 +1,7 @@
#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);
diff --git a/init/Kconfig b/init/Kconfig
index a4112e95724a..cf5b5a0dcbc2 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
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);
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 4904c4677000..aa0de240fb41 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -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))
--
2.19.1
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