[PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Lingutla Chandrasekhar]

If user updates any cpu's cpu_capacity, then the new value is going to
be applied to all its online sibling cpus. But this need not to be correct
always, as sibling cpus (in ARM, same micro architecture cpus) would have
different cpu_capacity with different performance characteristics.
So, updating the user supplied cpu_capacity to all cpu siblings
is not correct.

And another problem is, current code assumes that 'all cpus in a cluster
or with same package_id (core_siblings), would have same cpu_capacity'.
But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
cpu topology sibling masks")', when a cpu hotplugged out, the cpu
information gets cleared in its sibling cpus. So, user supplied
cpu_capacity would be applied to only online sibling cpus at the time.
After that, if any cpu hotplugged in, it would have different cpu_capacity
than its siblings, which breaks the above assumption.

So, instead of mucking around the core sibling mask for user supplied
value, use device-tree to set cpu capacity. And make the cpu_capacity
node as read-only to know the asymmetry between cpus in the system.
While at it, remove cpu_scale_mutex usage, which used for sysfs write
protection.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Quentin Perret <quentin.perret@arm.com>
Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index edfcf8d982e4..1739d7e1952a 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -7,7 +7,6 @@
  */
 
 #include <linux/acpi.h>
-#include <linux/arch_topology.h>
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/device.h>
@@ -31,7 +30,6 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
 		per_cpu(freq_scale, i) = scale;
 }
 
-static DEFINE_MUTEX(cpu_scale_mutex);
 DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
 
 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
@@ -51,37 +49,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
 static void update_topology_flags_workfn(struct work_struct *work);
 static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
 
-static ssize_t cpu_capacity_store(struct device *dev,
-				  struct device_attribute *attr,
-				  const char *buf,
-				  size_t count)
-{
-	struct cpu *cpu = container_of(dev, struct cpu, dev);
-	int this_cpu = cpu->dev.id;
-	int i;
-	unsigned long new_capacity;
-	ssize_t ret;
-
-	if (!count)
-		return 0;
-
-	ret = kstrtoul(buf, 0, &new_capacity);
-	if (ret)
-		return ret;
-	if (new_capacity > SCHED_CAPACITY_SCALE)
-		return -EINVAL;
-
-	mutex_lock(&cpu_scale_mutex);
-	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
-		topology_set_cpu_scale(i, new_capacity);
-	mutex_unlock(&cpu_scale_mutex);
-
-	schedule_work(&update_topology_flags_work);
-
-	return count;
-}
-
-static DEVICE_ATTR_RW(cpu_capacity);
+static DEVICE_ATTR_RO(cpu_capacity);
 
 static int register_cpu_capacity_sysctl(void)
 {
@@ -141,7 +109,6 @@ void topology_normalize_cpu_scale(void)
 		return;
 
 	pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
-	mutex_lock(&cpu_scale_mutex);
 	for_each_possible_cpu(cpu) {
 		pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
 			 cpu, raw_capacity[cpu]);
@@ -151,7 +118,6 @@ void topology_normalize_cpu_scale(void)
 		pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
 			cpu, topology_get_cpu_scale(NULL, cpu));
 	}
-	mutex_unlock(&cpu_scale_mutex);
 }
 
 bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
 a Linux Foundation Collaborative Project.

Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Mukesh Ojha]

Thanks for making the change suggested.

Should not this be v3.

Please add version detail properly including what changes you made in 
which version after ---,  that makes the patch easy to review.

Thanks.
Mukesh


On 3/28/2019 10:17 AM, Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So, updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
>
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So, user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hotplugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
>
> So, instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the asymmetry between cpus in the system.
> While at it, remove cpu_scale_mutex usage, which used for sysfs write
> protection.
>
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Tested-by: Quentin Perret <quentin.perret@arm.com>
> Reviewed-by: Quentin Perret <quentin.perret@arm.com>
> Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
>
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index edfcf8d982e4..1739d7e1952a 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -7,7 +7,6 @@
>    */
>   
>   #include <linux/acpi.h>
> -#include <linux/arch_topology.h>
>   #include <linux/cpu.h>
>   #include <linux/cpufreq.h>
>   #include <linux/device.h>
> @@ -31,7 +30,6 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
>   		per_cpu(freq_scale, i) = scale;
>   }
>   
> -static DEFINE_MUTEX(cpu_scale_mutex);
>   DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
>   
>   void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
> @@ -51,37 +49,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
>   static void update_topology_flags_workfn(struct work_struct *work);
>   static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
>   
> -static ssize_t cpu_capacity_store(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf,
> -				  size_t count)
> -{
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	int this_cpu = cpu->dev.id;
> -	int i;
> -	unsigned long new_capacity;
> -	ssize_t ret;
> -
> -	if (!count)
> -		return 0;
> -
> -	ret = kstrtoul(buf, 0, &new_capacity);
> -	if (ret)
> -		return ret;
> -	if (new_capacity > SCHED_CAPACITY_SCALE)
> -		return -EINVAL;
> -
> -	mutex_lock(&cpu_scale_mutex);
> -	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
> -		topology_set_cpu_scale(i, new_capacity);
> -	mutex_unlock(&cpu_scale_mutex);
> -
> -	schedule_work(&update_topology_flags_work);
> -
> -	return count;
> -}
> -
> -static DEVICE_ATTR_RW(cpu_capacity);
> +static DEVICE_ATTR_RO(cpu_capacity);
>   
>   static int register_cpu_capacity_sysctl(void)
>   {
> @@ -141,7 +109,6 @@ void topology_normalize_cpu_scale(void)
>   		return;
>   
>   	pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
> -	mutex_lock(&cpu_scale_mutex);
>   	for_each_possible_cpu(cpu) {
>   		pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
>   			 cpu, raw_capacity[cpu]);
> @@ -151,7 +118,6 @@ void topology_normalize_cpu_scale(void)
>   		pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
>   			cpu, topology_get_cpu_scale(NULL, cpu));
>   	}
> -	mutex_unlock(&cpu_scale_mutex);
>   }
>   
>   bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)

Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Greg KH]

On Thu, Mar 28, 2019 at 10:17:05AM +0530, Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So, updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
> 
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So, user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hotplugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
> 
> So, instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the asymmetry between cpus in the system.
> While at it, remove cpu_scale_mutex usage, which used for sysfs write
> protection.
> 
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Tested-by: Quentin Perret <quentin.perret@arm.com>
> Reviewed-by: Quentin Perret <quentin.perret@arm.com>
> Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

I see 3 "v2" patches in my queue, all different :(

Also, you need to list what changed below the --- line as the
documentation says to do so.  Please fix up and resend v3.

thanks,

greg k-h

[PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Lingutla Chandrasekhar]

If user updates any cpu's cpu_capacity, then the new value is going to
be applied to all its online sibling cpus. But this need not to be correct
always, as sibling cpus (in ARM, same micro architecture cpus) would have
different cpu_capacity with different performance characteristics.
So updating the user supplied cpu_capacity to all cpu siblings
is not correct.

And another problem is, current code assumes that 'all cpus in a cluster
or with same package_id (core_siblings), would have same cpu_capacity'.
But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
cpu topology sibling masks")', when a cpu hotplugged out, the cpu
information gets cleared in its sibling cpus. So user supplied
cpu_capacity would be applied to only online sibling cpus at the time.
After that, if any cpu hot plugged in, it would have different cpu_capacity
than its siblings, which breaks the above assumption.

So instead of mucking around the core sibling mask for user supplied
value, use device-tree to set cpu capacity. And make the cpu_capacity
node as read-only to know the assymetry between cpus in the system.
While at it, remove cpu_scale_mutex usage, which used for sysfs write
protection.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Tested-by: Quentin Perret <quentin.perret@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index edfcf8d982e4..1739d7e1952a 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -7,7 +7,6 @@
  */
 
 #include <linux/acpi.h>
-#include <linux/arch_topology.h>
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/device.h>
@@ -31,7 +30,6 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
 		per_cpu(freq_scale, i) = scale;
 }
 
-static DEFINE_MUTEX(cpu_scale_mutex);
 DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
 
 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
@@ -51,37 +49,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
 static void update_topology_flags_workfn(struct work_struct *work);
 static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
 
-static ssize_t cpu_capacity_store(struct device *dev,
-				  struct device_attribute *attr,
-				  const char *buf,
-				  size_t count)
-{
-	struct cpu *cpu = container_of(dev, struct cpu, dev);
-	int this_cpu = cpu->dev.id;
-	int i;
-	unsigned long new_capacity;
-	ssize_t ret;
-
-	if (!count)
-		return 0;
-
-	ret = kstrtoul(buf, 0, &new_capacity);
-	if (ret)
-		return ret;
-	if (new_capacity > SCHED_CAPACITY_SCALE)
-		return -EINVAL;
-
-	mutex_lock(&cpu_scale_mutex);
-	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
-		topology_set_cpu_scale(i, new_capacity);
-	mutex_unlock(&cpu_scale_mutex);
-
-	schedule_work(&update_topology_flags_work);
-
-	return count;
-}
-
-static DEVICE_ATTR_RW(cpu_capacity);
+static DEVICE_ATTR_RO(cpu_capacity);
 
 static int register_cpu_capacity_sysctl(void)
 {
@@ -141,7 +109,6 @@ void topology_normalize_cpu_scale(void)
 		return;
 
 	pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
-	mutex_lock(&cpu_scale_mutex);
 	for_each_possible_cpu(cpu) {
 		pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
 			 cpu, raw_capacity[cpu]);
@@ -151,7 +118,6 @@ void topology_normalize_cpu_scale(void)
 		pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
 			cpu, topology_get_cpu_scale(NULL, cpu));
 	}
-	mutex_unlock(&cpu_scale_mutex);
 }
 
 bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
 a Linux Foundation Collaborative Project.

Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Mukesh Ojha]

On 3/27/2019 5:27 PM, Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So updating the user supplied cpu_capacity to all cpu siblings
s/So/So,
> is not correct.
>
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So user supplied
--
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hot plugged in, it would have different cpu_capacity

s/hot plugged/hotplugged

> than its siblings, which breaks the above assumption.
>
> So instead of mucking around the core sibling mask for user supplied
--
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the assymetry between cpus in the system.
s/assymetry/asymmetry
> While at it, remove cpu_scale_mutex usage, which used for sysfs write
> protection.
>
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Tested-by: Quentin Perret <quentin.perret@arm.com>
> Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> Reviewed-by: Quentin Perret <quentin.perret@arm.com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Please fix the commit text minor comments.
otherwise , looks good.

Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
-Mukesh


>
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index edfcf8d982e4..1739d7e1952a 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -7,7 +7,6 @@
>    */
>   
>   #include <linux/acpi.h>
> -#include <linux/arch_topology.h>
>   #include <linux/cpu.h>
>   #include <linux/cpufreq.h>
>   #include <linux/device.h>
> @@ -31,7 +30,6 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
>   		per_cpu(freq_scale, i) = scale;
>   }
>   
> -static DEFINE_MUTEX(cpu_scale_mutex);
>   DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
>   
>   void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
> @@ -51,37 +49,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
>   static void update_topology_flags_workfn(struct work_struct *work);
>   static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
>   
> -static ssize_t cpu_capacity_store(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf,
> -				  size_t count)
> -{
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	int this_cpu = cpu->dev.id;
> -	int i;
> -	unsigned long new_capacity;
> -	ssize_t ret;
> -
> -	if (!count)
> -		return 0;
> -
> -	ret = kstrtoul(buf, 0, &new_capacity);
> -	if (ret)
> -		return ret;
> -	if (new_capacity > SCHED_CAPACITY_SCALE)
> -		return -EINVAL;
> -
> -	mutex_lock(&cpu_scale_mutex);
> -	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
> -		topology_set_cpu_scale(i, new_capacity);
> -	mutex_unlock(&cpu_scale_mutex);
> -
> -	schedule_work(&update_topology_flags_work);
> -
> -	return count;
> -}
> -
> -static DEVICE_ATTR_RW(cpu_capacity);
> +static DEVICE_ATTR_RO(cpu_capacity);
>   
>   static int register_cpu_capacity_sysctl(void)
>   {
> @@ -141,7 +109,6 @@ void topology_normalize_cpu_scale(void)
>   		return;
>   
>   	pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
> -	mutex_lock(&cpu_scale_mutex);
>   	for_each_possible_cpu(cpu) {
>   		pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
>   			 cpu, raw_capacity[cpu]);
> @@ -151,7 +118,6 @@ void topology_normalize_cpu_scale(void)
>   		pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
>   			cpu, topology_get_cpu_scale(NULL, cpu));
>   	}
> -	mutex_unlock(&cpu_scale_mutex);
>   }
>   
>   bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)

Re: [PATCH v1] arch_topology: Make cpu_capacity sysfs node as ready-only

[Dietmar Eggemann]

On 3/6/19 4:27 PM, Lingutla Chandrasekhar wrote:

[...]

> @@ -51,37 +50,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
>   static void update_topology_flags_workfn(struct work_struct *work);
>   static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
>   
> -static ssize_t cpu_capacity_store(struct device *dev,
> -				  struct device_attribute *attr,
> -				  const char *buf,
> -				  size_t count)
> -{
> -	struct cpu *cpu = container_of(dev, struct cpu, dev);
> -	int this_cpu = cpu->dev.id;
> -	int i;
> -	unsigned long new_capacity;
> -	ssize_t ret;
> -
> -	if (!count)
> -		return 0;
> -
> -	ret = kstrtoul(buf, 0, &new_capacity);
> -	if (ret)
> -		return ret;
> -	if (new_capacity > SCHED_CAPACITY_SCALE)
> -		return -EINVAL;
> -
> -	mutex_lock(&cpu_scale_mutex);

Since we can't write to cpu_scale from here anymore, we could get rid of 
cpu_scale_mutex. 
topology_normalize_cpu_scale()->topology_set_cpu_scale() is now only 
called from:

[    0.202628]  topology_normalize_cpu_scale+0x28/0x30
[    0.207529]  init_cpu_topology+0x168/0x1e8
[    0.211644]  smp_prepare_cpus+0x2c/0x108
[    0.215585]  kernel_init_freeable+0x104/0x518
[    0.219963]  kernel_init+0x18/0x110
[    0.223469]  ret_from_fork+0x10/0x1c

for dts capacity-dmips-mhz properties

and

[    3.130180]  topology_normalize_cpu_scale.part.0+0xac/0xd0
[    3.135619]  init_cpu_capacity_callback+0x100/0x178
[    3.140459]  notifier_call_chain+0x5c/0xa0
[    3.144522]  blocking_notifier_call_chain+0x64/0x88
[    3.149363]  cpufreq_set_policy+0xd8/0x3c8
[    3.153427]  cpufreq_init_policy+0x78/0xc8

for cpufreq max frequency related adjustments to cpu capacity.

The mutex was introduced for the sysfs interface here: 
https://lore.kernel.org/lkml/1468932048-31635-8-git-send-email-juri.lelli@arm.com

> -	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
> -		topology_set_cpu_scale(i, new_capacity);
> -	mutex_unlock(&cpu_scale_mutex);
> -
> -	schedule_work(&update_topology_flags_work);
> -
> -	return count;
> -}
> -
> -static DEVICE_ATTR_RW(cpu_capacity);
> +static DEVICE_ATTR_RO(cpu_capacity);
>   
>   static int register_cpu_capacity_sysctl(void)
>   {
> 

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

on Arm64 Juno with v5.0

[PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Lingutla Chandrasekhar]

If user updates any cpu's cpu_capacity, then the new value is going to
be applied to all its online sibling cpus. But this need not to be correct
always, as sibling cpus (in ARM, same micro architecture cpus) would have
different cpu_capacity with different performance characteristics.
So updating the user supplied cpu_capacity to all cpu siblings
is not correct.

And another problem is, current code assumes that 'all cpus in a cluster
or with same package_id (core_siblings), would have same cpu_capacity'.
But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
cpu topology sibling masks")', when a cpu hotplugged out, the cpu
information gets cleared in its sibling cpus. So user supplied
cpu_capacity would be applied to only online sibling cpus at the time.
After that, if any cpu hot plugged in, it would have different cpu_capacity
than its siblings, which breaks the above assumption.

So instead of mucking around the core sibling mask for user supplied
value, use device-tree to set cpu capacity. And make the cpu_capacity
node as read-only to know the assymetry between cpus in the system.
While at it, remove cpu_scale_mutex usage, which used for sysfs write
protection.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Acked-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
---

Changes from v1:
   - Removed cpu_scale_mutex usage, suggested by Dietmar Eggemann.
---
 drivers/base/arch_topology.c | 36 +-----------------------------------
 1 file changed, 1 insertion(+), 35 deletions(-)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index edfcf8d..1739d7e 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -7,7 +7,6 @@
  */
 
 #include <linux/acpi.h>
-#include <linux/arch_topology.h>
 #include <linux/cpu.h>
 #include <linux/cpufreq.h>
 #include <linux/device.h>
@@ -31,7 +30,6 @@ void arch_set_freq_scale(struct cpumask *cpus, unsigned long cur_freq,
 		per_cpu(freq_scale, i) = scale;
 }
 
-static DEFINE_MUTEX(cpu_scale_mutex);
 DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
 
 void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity)
@@ -51,37 +49,7 @@ static ssize_t cpu_capacity_show(struct device *dev,
 static void update_topology_flags_workfn(struct work_struct *work);
 static DECLARE_WORK(update_topology_flags_work, update_topology_flags_workfn);
 
-static ssize_t cpu_capacity_store(struct device *dev,
-				  struct device_attribute *attr,
-				  const char *buf,
-				  size_t count)
-{
-	struct cpu *cpu = container_of(dev, struct cpu, dev);
-	int this_cpu = cpu->dev.id;
-	int i;
-	unsigned long new_capacity;
-	ssize_t ret;
-
-	if (!count)
-		return 0;
-
-	ret = kstrtoul(buf, 0, &new_capacity);
-	if (ret)
-		return ret;
-	if (new_capacity > SCHED_CAPACITY_SCALE)
-		return -EINVAL;
-
-	mutex_lock(&cpu_scale_mutex);
-	for_each_cpu(i, &cpu_topology[this_cpu].core_sibling)
-		topology_set_cpu_scale(i, new_capacity);
-	mutex_unlock(&cpu_scale_mutex);
-
-	schedule_work(&update_topology_flags_work);
-
-	return count;
-}
-
-static DEVICE_ATTR_RW(cpu_capacity);
+static DEVICE_ATTR_RO(cpu_capacity);
 
 static int register_cpu_capacity_sysctl(void)
 {
@@ -141,7 +109,6 @@ void topology_normalize_cpu_scale(void)
 		return;
 
 	pr_debug("cpu_capacity: capacity_scale=%u\n", capacity_scale);
-	mutex_lock(&cpu_scale_mutex);
 	for_each_possible_cpu(cpu) {
 		pr_debug("cpu_capacity: cpu=%d raw_capacity=%u\n",
 			 cpu, raw_capacity[cpu]);
@@ -151,7 +118,6 @@ void topology_normalize_cpu_scale(void)
 		pr_debug("cpu_capacity: CPU%d cpu_capacity=%lu\n",
 			cpu, topology_get_cpu_scale(NULL, cpu));
 	}
-	mutex_unlock(&cpu_scale_mutex);
 }
 
 bool __init topology_parse_cpu_capacity(struct device_node *cpu_node, int cpu)
-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
 a Linux Foundation Collaborative Project.

Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only

[Quentin Perret]

Hi,

On Friday 08 Mar 2019 at 18:08:48 (+0530), Lingutla Chandrasekhar wrote:
> If user updates any cpu's cpu_capacity, then the new value is going to
> be applied to all its online sibling cpus. But this need not to be correct
> always, as sibling cpus (in ARM, same micro architecture cpus) would have
> different cpu_capacity with different performance characteristics.
> So updating the user supplied cpu_capacity to all cpu siblings
> is not correct.
> 
> And another problem is, current code assumes that 'all cpus in a cluster
> or with same package_id (core_siblings), would have same cpu_capacity'.
> But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove
> cpu topology sibling masks")', when a cpu hotplugged out, the cpu
> information gets cleared in its sibling cpus. So user supplied
> cpu_capacity would be applied to only online sibling cpus at the time.
> After that, if any cpu hot plugged in, it would have different cpu_capacity
> than its siblings, which breaks the above assumption.
> 
> So instead of mucking around the core sibling mask for user supplied
> value, use device-tree to set cpu capacity. And make the cpu_capacity
> node as read-only to know the assymetry between cpus in the system.
> While at it, remove cpu_scale_mutex usage, which used for sysfs write
> protection.
> 
> Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Acked-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>

Reviewed-by: Quentin Perret <quentin.perret@arm.com>
Tested-by: Quentin Perret <quentin.perret@arm.com>

Thanks for doing this,
Quentin