[PATCH v2 0/3] per cpu resume latency

[PATCH v2 0/3] per cpu resume latency

[Alex Shi]

V2 changes: remove #ifdef CONFIG_CPU_IDLE_GOV_MENU for func
dev_pm_qos_expose_latency_limit(), since we have CONFIG_PM.

---
cpu_dma_latency is designed to keep all cpu awake from deep c-state.
That is good keep system with short response latency. But sometime we
don't need all cpu power especially in a more and more multi-core day.
So set all cpu restless that lead to a big power waste.

A better way is to keep the short cpu response latency on needed cpu, 
while let other unnecesscary cpus go to deep idle. That is this 
patchset. We just use the pm_qos_resume_latency on cpu. Giving the 
short cpu latency on appointed cpu via setting value on
/sys/devices/system/cpu/cpuX/power/pm_qos_resume_latency_us
We can set we wanted latency value according to the value of
/sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
less related state's latency value. Then cpu can get to this state or
higher.

Here is some testing data on my dragonboard 410c, the latency of state1
is 280us. It has 4 cores.

Benchmark: cyclictest -t 1  -n -i 10000 -l 1000 -q --latency=10000

without the patch:
Latency (us) Min:     87 Act:  209 Avg:  205 Max:     239
With the patch and cpu0/power/pm_qos_resume_latency_us is lower than
280us, like any value between 1 to 279
benchmark result on cpu0:
Latency (us) Min:     82 Act:   91 Avg:   95 Max:     110
In repeat testing, the Avg latency always drop to half of vanilla kernel
value, as well as Max latency value, although sometime the Max latency
is similar with vanilla kernel. 

Also we could use the cpu_dma_latency to get the similar short latency.
But 'idlestate' show all cpu are restless. Here is the idle status 
compression between cpu_dma_latency and this feature:

To record idlestate
#./idlestat --trace -t 10 -f /tmp/mytracepmlat -p -c -w -- cyclictest -t 1  -n -i 10000 -l 1000 -q --latency=10000

To compare the idle state, the 'total' colum show cpu1~3 nearly stay
in WFI state with cpu_dma_latency. but w/ my patch, they can get about
10 second sleep in 'spc' state.
# ./idlestat --import -f /tmp/mytracepmlat -b /tmp/mytrace -r comparison
Log is 10.055305 secs long with 7514 events
Log is 10.055370 secs long with 7545 events
--------------------------------------------------------------------------------
| C-state  |   min    |   max    |   avg    |   total  | hits  |  over | under |
--------------------------------------------------------------------------------
| clusterA                                                                     |
--------------------------------------------------------------------------------
|      WFI |      2us |  12.88ms |   4.18ms |    9.76s |  2334 |     0 |     0 |
|          |     -2us |  -14.4ms |    -17us |  -72.5ms |    -8 |     0 |     0 |
--------------------------------------------------------------------------------
|             cpu0                                                             |
--------------------------------------------------------------------------------
|      WFI |      3us | 100.98ms |  26.81ms |   10.03s |   374 |     0 |     0 |
|          |     -1us |     -1us |   -350us |   +5.0ms |    +5 |     0 |     0 |
--------------------------------------------------------------------------------
|             cpu1                                                             |
--------------------------------------------------------------------------------
|      WFI |    280us |   3.96ms |   1.96ms |  19.64ms |    10 |     0 |     5 |
|          |   +221us | -891.7ms |   -9.1ms |    -9.9s |  -889 |     0 |     0 |
|      spc |    234us |  19.71ms |   9.79ms |    9.91s |  1012 |     4 |     0 |
|          |   +167us |  +17.9ms |   +8.6ms |    +9.9s | +1009 |    +1 |     0 |
--------------------------------------------------------------------------------
|             cpu2                                                             |
--------------------------------------------------------------------------------
|      WFI |     86us |   1.01ms |    637us |   1.91ms |     3 |     0 |     0 |
|          |    -16us |  -26.5ms |   -8.8ms |   -10.0s | -1057 |     0 |     0 |
|      spc |    930us |  47.67ms |  10.05ms |    9.92s |   987 |     2 |     0 |
|          |   -1.4ms |  +43.7ms |   +6.9ms |    +9.9s |  +985 |    +2 |     0 |
--------------------------------------------------------------------------------
|             cpu3                                                             |
--------------------------------------------------------------------------------
|      WFI |      0us |      0us |      0us |      0us |     0 |     0 |     0 |
|          |          |    -4.0s | -152.1ms |   -10.0s |   -66 |     0 |     0 |
|      spc |    420us |    3.50s | 913.74ms |   10.05s |    11 |     3 |     0 |
|          |   -891us |    +3.5s | +911.0ms |   +10.0s |    +8 |    +1 |     0 |
--------------------------------------------------------------------------------

Thanks
Alex

[PATCH 1/3] cpuidle/menu: stop seeking deeper idle if current state is too deep

[Alex Shi]

The obsolete commit 71abbbf85 want to introduce a dynamic cstates,
but it was removed for long time. Just left the nonsense deeper cstate
checking.

Since all target_residency and exit_latency are going longer in deeper
idle state, no needs to waste some cpu cycle on useless seeking.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
Acked-by: Rik van Riel <riel@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/menu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index d9b5b93..07e36bb 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -357,9 +357,9 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		if (s->disabled || su->disable)
 			continue;
 		if (s->target_residency > data->predicted_us)
-			continue;
+			break;
 		if (s->exit_latency > latency_req)
-			continue;
+			break;
 
 		data->last_state_idx = i;
 	}
-- 
2.8.1.101.g72d917a

[PATCH v2 2/3] cpu: expose pm_qos_resume_latency for each cpu

[Alex Shi]

The cpu-dma PM QoS constraint impacts all the cpus in the system. There
is no way to let the user to choose a PM QoS constraint per cpu.

The following patch exposes to the userspace a per cpu based sysfs file
in order to let the userspace to change the value of the PM QoS latency
constraint.

This change is inoperative in its form and the cpuidle governors have to
take into account the per cpu latency constraint in addition to the
global cpu-dma latency constraint in order to operate properly.

BTW
The pm_qos_resume_latency usage defined in
Documentation/ABI/testing/sysfs-devices-power
The /sys/devices/.../power/pm_qos_resume_latency_us attribute
contains the PM QoS resume latency limit for the given device,
which is the maximum allowed time it can take to resume the
device, after it has been suspended at run time, from a resume
request to the moment the device will be ready to process I/O,
in microseconds.  If it is equal to 0, however, this means that
the PM QoS resume latency may be arbitrary.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
To: linux-kernel@vger.kernel.org
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-pm@vger.kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
---
 drivers/base/cpu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c28e1a..2c3b359 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -17,6 +17,7 @@
 #include <linux/of.h>
 #include <linux/cpufeature.h>
 #include <linux/tick.h>
+#include <linux/pm_qos.h>
 
 #include "base.h"
 
@@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
 
 	per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	register_cpu_under_node(num, cpu_to_node(num));
+	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
 
 	return 0;
 }
-- 
2.8.1.101.g72d917a

Re: [PATCH v2 2/3] cpu: expose pm_qos_resume_latency for each cpu

[Daniel Lezcano]

On Thu, Jan 12, 2017 at 09:27:03PM +0800, Alex Shi wrote:
> The cpu-dma PM QoS constraint impacts all the cpus in the system. There
> is no way to let the user to choose a PM QoS constraint per cpu.
> 
> The following patch exposes to the userspace a per cpu based sysfs file
> in order to let the userspace to change the value of the PM QoS latency
> constraint.
> 
> This change is inoperative in its form and the cpuidle governors have to
> take into account the per cpu latency constraint in addition to the
> global cpu-dma latency constraint in order to operate properly.
> 
> BTW
> The pm_qos_resume_latency usage defined in
> Documentation/ABI/testing/sysfs-devices-power
> The /sys/devices/.../power/pm_qos_resume_latency_us attribute
> contains the PM QoS resume latency limit for the given device,
> which is the maximum allowed time it can take to resume the
> device, after it has been suspended at run time, from a resume
> request to the moment the device will be ready to process I/O,
> in microseconds.  If it is equal to 0, however, this means that
> the PM QoS resume latency may be arbitrary.
> 
> Signed-off-by: Alex Shi <alex.shi@linaro.org>
> To: linux-kernel@vger.kernel.org
> To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: linux-pm@vger.kernel.org
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> ---
>  drivers/base/cpu.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 4c28e1a..2c3b359 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -17,6 +17,7 @@
>  #include <linux/of.h>
>  #include <linux/cpufeature.h>
>  #include <linux/tick.h>
> +#include <linux/pm_qos.h>
>  
>  #include "base.h"
>  
> @@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
>  
>  	per_cpu(cpu_sys_devices, num) = &cpu->dev;
>  	register_cpu_under_node(num, cpu_to_node(num));
> +	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);

This patch should be submitted as the last patch in the latencies constraint
changes patchset IMO. It is pointless to provide an interface before a
feature which is still under discussion.


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Re: [PATCH v2 2/3] cpu: expose pm_qos_resume_latency for each cpu

[Alex Shi]

On 01/17/2017 06:23 PM, Daniel Lezcano wrote:
>> >  
>> > @@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
>> >  
>> >  	per_cpu(cpu_sys_devices, num) = &cpu->dev;
>> >  	register_cpu_under_node(num, cpu_to_node(num));
>> > +	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
> This patch should be submitted as the last patch in the latencies constraint
> changes patchset IMO. It is pointless to provide an interface before a
> feature which is still under discussion.

Thanks for comments!

will fold it into next patch!

[PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

Kernel or user may have special requirement on cpu response time, like
if a interrupt is pinned to a cpu, we don't want the cpu goes too deep
sleep. This patch can prevent this thing happen by consider per cpu
resume_latency setting in cpu sleep state selection in menu governor.

The pm_qos_resume_latency ask device to give reponse in this time. That's
similar with cpu cstates' entry_latency + exit_latency. But since
most of cpu cstate either has no entry_latency or add it into exit_latency
So, we just can restrict this time requirement as states exit_latency.

We can set a wanted latency value according to the value of
/sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
less than related state's latency value. Then cpu can get to this state
or higher.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
To: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/menu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 07e36bb..8d6d25c 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -19,6 +19,7 @@
 #include <linux/tick.h>
 #include <linux/sched.h>
 #include <linux/math64.h>
+#include <linux/cpu.h>
 
 /*
  * Please note when changing the tuning values:
@@ -280,17 +281,23 @@ static unsigned int get_typical_interval(struct menu_device *data)
 static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = this_cpu_ptr(&menu_devices);
+	struct device *device = get_cpu_device(dev->cpu);
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 	unsigned int interactivity_req;
 	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
+	int resume_latency = dev_pm_qos_read_value(device);
 
 	if (data->needs_update) {
 		menu_update(drv, dev);
 		data->needs_update = 0;
 	}
 
+	/* resume_latency is 0 means no restriction */
+	if (resume_latency && resume_latency < latency_req)
+		latency_req = resume_latency;
+
 	/* Special case when user has set very strict latency requirement */
 	if (unlikely(latency_req == 0))
 		return 0;
-- 
2.8.1.101.g72d917a

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Rik van Riel]

[-- Attachment #1: Type: text/plain, Size: 1374 bytes --]

On Thu, 2017-01-12 at 21:27 +0800, Alex Shi wrote:
> Kernel or user may have special requirement on cpu response time,
> like
> if a interrupt is pinned to a cpu, we don't want the cpu goes too
> deep
> sleep. This patch can prevent this thing happen by consider per cpu
> resume_latency setting in cpu sleep state selection in menu governor.
> 
> The pm_qos_resume_latency ask device to give reponse in this time.
> That's
> similar with cpu cstates' entry_latency + exit_latency. But since
> most of cpu cstate either has no entry_latency or add it into
> exit_latency
> So, we just can restrict this time requirement as states
> exit_latency.
> 
> We can set a wanted latency value according to the value of
> /sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
> less than related state's latency value. Then cpu can get to this
> state
> or higher.
> 
> Signed-off-by: Alex Shi <alex.shi@linaro.org>
> To: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> 

Acked-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 473 bytes --]

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

Thanks a lot, Rik!

Anyone like to give more comments or pick it up?

Regards
Alex

On 01/13/2017 04:03 AM, Rik van Riel wrote:
> Acked-by: Rik van Riel <riel@redhat.com>

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Daniel Lezcano]

On Thu, Jan 12, 2017 at 09:27:04PM +0800, Alex Shi wrote:
> Kernel or user may have special requirement on cpu response time, like
> if a interrupt is pinned to a cpu, we don't want the cpu goes too deep
> sleep. This patch can prevent this thing happen by consider per cpu
> resume_latency setting in cpu sleep state selection in menu governor.
> 
> The pm_qos_resume_latency ask device to give reponse in this time. That's
> similar with cpu cstates' entry_latency + exit_latency. But since
> most of cpu cstate either has no entry_latency or add it into exit_latency
> So, we just can restrict this time requirement as states exit_latency.
> 
> We can set a wanted latency value according to the value of
> /sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
> less than related state's latency value. Then cpu can get to this state
> or higher.
> 
> Signed-off-by: Alex Shi <alex.shi@linaro.org>
> To: linux-kernel@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> ---
>  drivers/cpuidle/governors/menu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
> index 07e36bb..8d6d25c 100644
> --- a/drivers/cpuidle/governors/menu.c
> +++ b/drivers/cpuidle/governors/menu.c
> @@ -19,6 +19,7 @@
>  #include <linux/tick.h>
>  #include <linux/sched.h>
>  #include <linux/math64.h>
> +#include <linux/cpu.h>
>  
>  /*
>   * Please note when changing the tuning values:
> @@ -280,17 +281,23 @@ static unsigned int get_typical_interval(struct menu_device *data)
>  static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
>  {
>  	struct menu_device *data = this_cpu_ptr(&menu_devices);
> +	struct device *device = get_cpu_device(dev->cpu);
>  	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
>  	int i;
>  	unsigned int interactivity_req;
>  	unsigned int expected_interval;
>  	unsigned long nr_iowaiters, cpu_load;
> +	int resume_latency = dev_pm_qos_read_value(device);
>  
>  	if (data->needs_update) {
>  		menu_update(drv, dev);
>  		data->needs_update = 0;
>  	}
>  
> +	/* resume_latency is 0 means no restriction */
> +	if (resume_latency && resume_latency < latency_req)
> +		latency_req = resume_latency;
> +

Calling dev_pm_qos_read_value() after checking latency_req is different from
zero would make more sense. If a zero latency is expected, no need to add an
overhead as we will return zero in all the cases.

	if (unlikely(latency_req == 0))
		return 0;

	device = get_cpu_device(dev->cpu);

	resume_latency = dev_pm_qos_read_value(device);
	if (resume_latency)
		latency_req = min(latency_req, resume_latency);

That said, I have the feeling that is taking the wrong direction. Each time we
are entering idle, we check the latencies. Entering idle can be done thousand
of times per second. Wouldn't make sense to disable the states not fulfilling
the constraints at the moment the latencies are changed ? As the idle states
have increasing exit latencies, setting an idle state limit to disable all
states after that limit may be more efficient than checking again and again in
the idle path, no ?

For example, a zero PM_QOS_CPU_DMA_LATENCY latency should prevent to enter the
select's idle routine.

>  	/* Special case when user has set very strict latency requirement */
>  	if (unlikely(latency_req == 0))
>  		return 0;
> -- 
> 2.8.1.101.g72d917a
> 

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Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

> That said, I have the feeling that is taking the wrong direction. Each time we
> are entering idle, we check the latencies. Entering idle can be done thousand
> of times per second. Wouldn't make sense to disable the states not fulfilling
> the constraints at the moment the latencies are changed ? As the idle states
> have increasing exit latencies, setting an idle state limit to disable all
> states after that limit may be more efficient than checking again and again in
> the idle path, no ?

You'r right. save some checking is good thing to do.


>From 9e1cc3e02b8d954e606dd5a0f6466a8d5b3efab7 Mon Sep 17 00:00:00 2001
From: Alex Shi <alex.shi@linaro.org>
Date: Wed, 26 Oct 2016 15:26:22 +0800
Subject: [PATCH 2/2] cpuidle/menu: add per cpu pm_qos_resume_latency
 consideration

Kernel or user may have special requirement on cpu response time, like
if a interrupt is pinned to a cpu, we don't want the cpu goes too deep
sleep. This patch can prevent this thing happen by consider per cpu
resume_latency setting in cpu sleep state selection in menu governor.

The pm_qos_resume_latency ask device to give reponse in this time. That's
similar with cpu cstates' entry_latency + exit_latency. But since
most of cpu cstate either has no entry_latency or add it into exit_latency
So, we just can restrict this time requirement as states exit_latency.

We can set a wanted latency value according to the value of
/sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
less than related state's latency value. Then cpu can get to this state
or higher.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
Acked-by: Rik van Riel <riel@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
---
 drivers/base/cpu.c               |  2 ++
 drivers/cpuidle/governors/menu.c | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index 4c28e1a..2c3b359 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -17,6 +17,7 @@
 #include <linux/of.h>
 #include <linux/cpufeature.h>
 #include <linux/tick.h>
+#include <linux/pm_qos.h>
 
 #include "base.h"
 
@@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num)
 
 	per_cpu(cpu_sys_devices, num) = &cpu->dev;
 	register_cpu_under_node(num, cpu_to_node(num));
+	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);
 
 	return 0;
 }
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 07e36bb..cc7d873 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -19,6 +19,7 @@
 #include <linux/tick.h>
 #include <linux/sched.h>
 #include <linux/math64.h>
+#include <linux/cpu.h>
 
 /*
  * Please note when changing the tuning values:
@@ -280,11 +281,13 @@ static unsigned int get_typical_interval(struct menu_device *data)
 static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = this_cpu_ptr(&menu_devices);
+	struct device *device;
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 	unsigned int interactivity_req;
 	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
+	int resume_latency;
 
 	if (data->needs_update) {
 		menu_update(drv, dev);
@@ -295,6 +298,13 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (unlikely(latency_req == 0))
 		return 0;
 
+	device = get_cpu_device(dev->cpu);
+
+	/* resume_latency is 0 means no restriction */
+	resume_latency = dev_pm_qos_read_value(device);
+	if (resume_latency)
+		latency_req = min(latency_req, resume_latency);
+
 	/* determine the expected residency time, round up */
 	data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length());
 
-- 
2.8.1.101.g72d917a

> 
> For example, a zero PM_QOS_CPU_DMA_LATENCY latency should prevent to enter the
> select's idle routine.

That's a good idea. I will give a draft change to review! :)

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Daniel Lezcano]

On Thu, Jan 19, 2017 at 05:25:37PM +0800, Alex Shi wrote:
> 
> > That said, I have the feeling that is taking the wrong direction. Each time we
> > are entering idle, we check the latencies. Entering idle can be done thousand
> > of times per second. Wouldn't make sense to disable the states not fulfilling
> > the constraints at the moment the latencies are changed ? As the idle states
> > have increasing exit latencies, setting an idle state limit to disable all
> > states after that limit may be more efficient than checking again and again in
> > the idle path, no ?
> 
> You'r right. save some checking is good thing to do.

Hi Alex,

I think you missed the point.

What I am proposing is to change the current approach by disabling all the
states after a specific latency.

We add a specific internal function:

static int cpuidle_set_latency(struct cpuidle_driver *drv,
				struct cpuidle_device *dev,
				int latency)
{
	int i, idx;

	for (i = 0, idx = 0; i < drv->state_count; i++) {

		struct cpuidle_state *s = &drv->states[i];			

		if (s->latency > latency)
			break;

		idx = i;
	}

	dev->state_count = idx;

	return 0;
}

This function is called from the notifier callback:

static int cpuidle_latency_notify(struct notifier_block *b,
                unsigned long l, void *v)
 {
-       wake_up_all_idle_cpus();
+       struct cpuidle_device *dev;
+       struct cpuidle_driver *drv;
+
+       cpuidle_pause_and_lock();
+       for_each_possible_cpu(cpu) {
+               dev = &per_cpu(cpuidle_dev, cpu);
+               drv = = cpuidle_get_cpu_driver(dev);    
+               cpuidle_set_latency(drv, dev, l)
+       }
+       cpuidle_resume_and_unlock();
+
        return NOTIFY_OK;
 }

-----------------------------------------------------------------------------

The menu governor becomes:

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index bba3c2af..87e58e3 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -352,7 +352,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
         * Find the idle state with the lowest power while satisfying
         * our constraints.
         */
-       for (i = data->last_state_idx + 1; i < drv->state_count; i++) {
+       for (i = data->last_state_idx + 1; i < dev->state_count; i++) {
                struct cpuidle_state *s = &drv->states[i];
                struct cpuidle_state_usage *su = &dev->states_usage[i];


... with a cleanup around latency_req.

-----------------------------------------------------------------------------

And the cpuidle_device structure is changed to:

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index b923c32..2fc966cb 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -88,6 +88,7 @@ struct cpuidle_device {
        cpumask_t               coupled_cpus;
        struct cpuidle_coupled  *coupled;
 #endif
+       int state_count;
 };
 
 DECLARE_PER_CPU(struct cpuidle_device *, cpuidle_devices);


At init time, the drv->state_count and all cpu's dev->state_count are the same.

Well, that is the rough idea: instead of reading the latency when entering
idle, let's disable/enable the idle states when we set a new latency.

I did not check how that fits with the per cpu latency, but I think it will be
cleaner to change the approach rather than spreading latencies dances around.

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Rafael J. Wysocki]

On Thu, Jan 19, 2017 at 11:21 AM, Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
> On Thu, Jan 19, 2017 at 05:25:37PM +0800, Alex Shi wrote:
>>
>> > That said, I have the feeling that is taking the wrong direction. Each time we
>> > are entering idle, we check the latencies. Entering idle can be done thousand
>> > of times per second. Wouldn't make sense to disable the states not fulfilling
>> > the constraints at the moment the latencies are changed ? As the idle states
>> > have increasing exit latencies, setting an idle state limit to disable all
>> > states after that limit may be more efficient than checking again and again in
>> > the idle path, no ?
>>
>> You'r right. save some checking is good thing to do.
>
> Hi Alex,
>
> I think you missed the point.
>
> What I am proposing is to change the current approach by disabling all the
> states after a specific latency.
>
> We add a specific internal function:
>
> static int cpuidle_set_latency(struct cpuidle_driver *drv,
>                                 struct cpuidle_device *dev,
>                                 int latency)
> {
>         int i, idx;
>
>         for (i = 0, idx = 0; i < drv->state_count; i++) {
>
>                 struct cpuidle_state *s = &drv->states[i];
>
>                 if (s->latency > latency)
>                         break;
>
>                 idx = i;
>         }
>
>         dev->state_count = idx;
>
>         return 0;
> }
>
> This function is called from the notifier callback:
>
> static int cpuidle_latency_notify(struct notifier_block *b,
>                 unsigned long l, void *v)
>  {
> -       wake_up_all_idle_cpus();
> +       struct cpuidle_device *dev;
> +       struct cpuidle_driver *drv;
> +
> +       cpuidle_pause_and_lock();
> +       for_each_possible_cpu(cpu) {
> +               dev = &per_cpu(cpuidle_dev, cpu);
> +               drv = = cpuidle_get_cpu_driver(dev);
> +               cpuidle_set_latency(drv, dev, l)
> +       }
> +       cpuidle_resume_and_unlock();
> +
>         return NOTIFY_OK;
>  }

The above may be problematic if the constraints change relatively
often.  It is global and it will affect all of the CPUs in the system
every time and now think about systems with hundreds of them.

Thanks,
Rafael

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

On 01/20/2017 05:43 AM, Rafael J. Wysocki wrote:
> The above may be problematic if the constraints change relatively
> often.  It is global and it will affect all of the CPUs in the system
> every time and now think about systems with hundreds of them.

Yes, the disadvantage is waking up all idle cpus when value changed. As
to the multi core concern, maybe a per cpu notifier way is better? But
that's another story of pm_qos...

So Rafael, any comments for this patch version?

Regards
Alex

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Daniel Lezcano]

On Thu, Jan 19, 2017 at 10:43:23PM +0100, Rafael J. Wysocki wrote:

[ ... ]

> > This function is called from the notifier callback:
> >
> > static int cpuidle_latency_notify(struct notifier_block *b,
> >                 unsigned long l, void *v)
> >  {
> > -       wake_up_all_idle_cpus();
> > +       struct cpuidle_device *dev;
> > +       struct cpuidle_driver *drv;
> > +
> > +       cpuidle_pause_and_lock();
> > +       for_each_possible_cpu(cpu) {
> > +               dev = &per_cpu(cpuidle_dev, cpu);
> > +               drv = = cpuidle_get_cpu_driver(dev);
> > +               cpuidle_set_latency(drv, dev, l)
> > +       }
> > +       cpuidle_resume_and_unlock();
> > +
> >         return NOTIFY_OK;
> >  }
> 
> The above may be problematic if the constraints change relatively
> often.  It is global and it will affect all of the CPUs in the system
> every time and now think about systems with hundreds of them.

Yeah, that could be problematic. The code snippet gives the general idea but it
could be changed by for example by a flag telling the cpus when they enter idle
to update their state_count. Or something like that.

But if you think the patchset is fine, it is ok, we can improve things afterwards.

  -- Daniel

-- 

 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

> Yeah, that could be problematic. The code snippet gives the general idea but it
> could be changed by for example by a flag telling the cpus when they enter idle
> to update their state_count. Or something like that.

Yes, this idea could be helpful.

But since the idle path isn't a hot path. and a few memory access won't 
cost a lot. So I doubt if the benefit could be measurable.


>
> But if you think the patchset is fine, it is ok, we can improve things afterwards.
>

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Daniel Lezcano]

On Sun, Jan 22, 2017 at 09:31:44AM +0800, Alex Shi wrote:
> 
> >Yeah, that could be problematic. The code snippet gives the general idea but it
> >could be changed by for example by a flag telling the cpus when they enter idle
> >to update their state_count. Or something like that.
> 
> Yes, this idea could be helpful.
> 
> But since the idle path isn't a hot path. and a few memory access won't cost
> a lot. So I doubt if the benefit could be measurable.

It won't be measurable, as well as reading the cpu device latency before
checking the latency req is zero, but it makes sense.

The idle routine is not a hot path but a very special place where the interrupt
are disabled, the rcu is not usable, tick is disabled etc ...

Perhaps it is not a problem for the moment, but it is probably worth to mention that
using API from other subsystems in the idle select path could be problematic
and perhaps it is time to think about another approach for the future.

-- 

 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

Re: [PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

On 01/23/2017 08:50 PM, Daniel Lezcano wrote:
> On Sun, Jan 22, 2017 at 09:31:44AM +0800, Alex Shi wrote:
>>
>>> Yeah, that could be problematic. The code snippet gives the general idea but it
>>> could be changed by for example by a flag telling the cpus when they enter idle
>>> to update their state_count. Or something like that.
>>
>> Yes, this idea could be helpful.
>>
>> But since the idle path isn't a hot path. and a few memory access won't cost
>> a lot. So I doubt if the benefit could be measurable.
> 
> It won't be measurable, as well as reading the cpu device latency before
> checking the latency req is zero, but it makes sense.

Just simple change the cpu state may make it looks unnatural. :)
> 
> The idle routine is not a hot path but a very special place where the interrupt
> are disabled, the rcu is not usable, tick is disabled etc ...
> 
> Perhaps it is not a problem for the moment, but it is probably worth to mention that
> using API from other subsystems in the idle select path could be problematic
> and perhaps it is time to think about another approach for the future.
> 

Yes, before idle, it did consider lots of parts, included pm qos for
long time... :)

[PATCH 3/3] cpuidle/menu: add per cpu pm_qos_resume_latency consideration

[Alex Shi]

Kernel or user may have special requirement on cpu response time, like
if a interrupt is pinned to a cpu, we don't want the cpu goes too deep
sleep. This patch can prevent this thing happen by consider per cpu
resume_latency setting in cpu sleep state selection in menu governor.

The pm_qos_resume_latency ask device to give reponse in this time. That's
similar with cpu cstates' entry_latency + exit_latency. But since
most of cpu cstate either has no entry_latency or add it into exit_latency
So, we just can restrict this time requirement as states exit_latency.

The 0 value of pm_qos_resume_latency is for no limitation according ABI
definition. So set the value 1 could get the 0 latency if it's needed.

Signed-off-by: Alex Shi <alex.shi@linaro.org>
To: linux-kernel@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/menu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 07e36bb..8d6d25c 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -19,6 +19,7 @@
 #include <linux/tick.h>
 #include <linux/sched.h>
 #include <linux/math64.h>
+#include <linux/cpu.h>
 
 /*
  * Please note when changing the tuning values:
@@ -280,17 +281,23 @@ static unsigned int get_typical_interval(struct menu_device *data)
 static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = this_cpu_ptr(&menu_devices);
+	struct device *device = get_cpu_device(dev->cpu);
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
 	int i;
 	unsigned int interactivity_req;
 	unsigned int expected_interval;
 	unsigned long nr_iowaiters, cpu_load;
+	int resume_latency = dev_pm_qos_read_value(device);
 
 	if (data->needs_update) {
 		menu_update(drv, dev);
 		data->needs_update = 0;
 	}
 
+	/* resume_latency is 0 means no restriction */
+	if (resume_latency && resume_latency < latency_req)
+		latency_req = resume_latency;
+
 	/* Special case when user has set very strict latency requirement */
 	if (unlikely(latency_req == 0))
 		return 0;
-- 
2.8.1.101.g72d917a