[PATCH v2 0/2] sched: Miscellaneous isolation related cleanups

[PATCH v2 0/2] sched: Miscellaneous isolation related cleanups

[Waiman Long]

 v2:
  - Remove HK_TYPE_SCHED and related dead code
  - Change consolidated name from HK_TYPE_NOHZ_FULL to
    HK_TYPE_KERNEL_NOSISE as suggested by Frederic and update
    isolation.c as well.

This series contains a number of miscellaneous sched/isolation related
cleanups.

[v1] https://lore.kernel.org/lkml/20240818234520.90186-1-longman@redhat.com/

Waiman Long (2):
  sched/core: Remove HK_TYPE_SCHED
  sched/isolation: Consolidate housekeeping cpumasks that are always
    identical

 include/linux/sched/isolation.h | 19 ++++++++++++-------
 kernel/sched/fair.c             | 14 --------------
 kernel/sched/isolation.c        | 10 ++--------
 3 files changed, 14 insertions(+), 29 deletions(-)

-- 
2.43.5

[PATCH v2 1/2] sched/core: Remove HK_TYPE_SCHED

[Waiman Long]

The HK_TYPE_SCHED housekeeping type is defined but not set anywhere. So
any code that try to use HK_TYPE_SCHED are essentially dead code. So
remove HK_TYPE_SCHED and any code that use it.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/linux/sched/isolation.h |  1 -
 kernel/sched/fair.c             | 14 --------------
 kernel/sched/isolation.c        |  1 -
 3 files changed, 16 deletions(-)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index 2b461129d1fa..499d5e480882 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -10,7 +10,6 @@ enum hk_type {
 	HK_TYPE_TIMER,
 	HK_TYPE_RCU,
 	HK_TYPE_MISC,
-	HK_TYPE_SCHED,
 	HK_TYPE_TICK,
 	HK_TYPE_DOMAIN,
 	HK_TYPE_WQ,
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9057584ec06d..ac5ed846fb55 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11840,9 +11840,6 @@ static inline int on_null_domain(struct rq *rq)
  * - When one of the busy CPUs notices that there may be an idle rebalancing
  *   needed, they will kick the idle load balancer, which then does idle
  *   load balancing for all the idle CPUs.
- *
- * - HK_TYPE_MISC CPUs are used for this task, because HK_TYPE_SCHED is not set
- *   anywhere yet.
  */
 static inline int find_new_ilb(void)
 {
@@ -12087,10 +12084,6 @@ void nohz_balance_enter_idle(int cpu)
 	if (!cpu_active(cpu))
 		return;
 
-	/* Spare idle load balancing on CPUs that don't want to be disturbed: */
-	if (!housekeeping_cpu(cpu, HK_TYPE_SCHED))
-		return;
-
 	/*
 	 * Can be set safely without rq->lock held
 	 * If a clear happens, it will have evaluated last additions because
@@ -12310,13 +12303,6 @@ static void nohz_newidle_balance(struct rq *this_rq)
 {
 	int this_cpu = this_rq->cpu;
 
-	/*
-	 * This CPU doesn't want to be disturbed by scheduler
-	 * housekeeping
-	 */
-	if (!housekeeping_cpu(this_cpu, HK_TYPE_SCHED))
-		return;
-
 	/* Will wake up very soon. No time for doing anything else*/
 	if (this_rq->avg_idle < sysctl_sched_migration_cost)
 		return;
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 5891e715f00d..5345e11f3d44 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -12,7 +12,6 @@ enum hk_flags {
 	HK_FLAG_TIMER		= BIT(HK_TYPE_TIMER),
 	HK_FLAG_RCU		= BIT(HK_TYPE_RCU),
 	HK_FLAG_MISC		= BIT(HK_TYPE_MISC),
-	HK_FLAG_SCHED		= BIT(HK_TYPE_SCHED),
 	HK_FLAG_TICK		= BIT(HK_TYPE_TICK),
 	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
 	HK_FLAG_WQ		= BIT(HK_TYPE_WQ),
-- 
2.43.5

[PATCH v2 2/2] sched/isolation: Consolidate housekeeping cpumasks that are always identical

[Waiman Long]

The housekeeping cpumasks are only set by two boot commandline
parameters: "nohz_full" and "isolcpus". When there is more than one of
"nohz_full" or "isolcpus", the extra ones must have the same CPU list
or the setup will fail partially.

The HK_TYPE_TICK, HK_TYPE_DOMAIN and HK_TYPE_MANAGED_IRQ types are
settable by "isolcpus" and they can be set individually. The other
housekeeping types are all set by "nohz_full" without a way to set them
individually. So they all have identical cpumasks.

There is actually no point in having different cpumasks for these
"nohz_full" only housekeeping types. Consolidate these types to use the
same cpumask by aliasing them to the same value. If there is a need to
set any of them independently in the future, we can break them out to
their own cpumasks again.

With this change, the number of cpumasks in the housekeeping structure
drops from 9 to 4.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/linux/sched/isolation.h | 18 ++++++++++++------
 kernel/sched/isolation.c        |  9 ++-------
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
index 499d5e480882..e2c42172de82 100644
--- a/include/linux/sched/isolation.h
+++ b/include/linux/sched/isolation.h
@@ -7,15 +7,21 @@
 #include <linux/tick.h>
 
 enum hk_type {
-	HK_TYPE_TIMER,
-	HK_TYPE_RCU,
-	HK_TYPE_MISC,
 	HK_TYPE_TICK,
 	HK_TYPE_DOMAIN,
-	HK_TYPE_WQ,
 	HK_TYPE_MANAGED_IRQ,
-	HK_TYPE_KTHREAD,
-	HK_TYPE_MAX
+	HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_MAX,
+
+	/*
+	 * The following housekeeping types are only set by the nohz_full
+	 * boot commandline option. So they can share the same value.
+	 */
+	HK_TYPE_TIMER   = HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_RCU     = HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_MISC    = HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_WQ      = HK_TYPE_KERNEL_NOISE,
+	HK_TYPE_KTHREAD = HK_TYPE_KERNEL_NOISE
 };
 
 #ifdef CONFIG_CPU_ISOLATION
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 5345e11f3d44..2b654272edcd 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -9,14 +9,10 @@
  */
 
 enum hk_flags {
-	HK_FLAG_TIMER		= BIT(HK_TYPE_TIMER),
-	HK_FLAG_RCU		= BIT(HK_TYPE_RCU),
-	HK_FLAG_MISC		= BIT(HK_TYPE_MISC),
 	HK_FLAG_TICK		= BIT(HK_TYPE_TICK),
 	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
-	HK_FLAG_WQ		= BIT(HK_TYPE_WQ),
 	HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
-	HK_FLAG_KTHREAD		= BIT(HK_TYPE_KTHREAD),
+	HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
 };
 
 DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
@@ -194,8 +190,7 @@ static int __init housekeeping_nohz_full_setup(char *str)
 {
 	unsigned long flags;
 
-	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
-		HK_FLAG_MISC | HK_FLAG_KTHREAD;
+	flags = HK_FLAG_KERNEL_NOISE;
 
 	return housekeeping_setup(str, flags);
 }
-- 
2.43.5

Re: [PATCH v2 2/2] sched/isolation: Consolidate housekeeping cpumasks that are always identical

[Phil Auld]

On Wed, Sep 04, 2024 at 01:14:41PM -0400 Waiman Long wrote:
> The housekeeping cpumasks are only set by two boot commandline
> parameters: "nohz_full" and "isolcpus". When there is more than one of
> "nohz_full" or "isolcpus", the extra ones must have the same CPU list
> or the setup will fail partially.
> 
> The HK_TYPE_TICK, HK_TYPE_DOMAIN and HK_TYPE_MANAGED_IRQ types are
> settable by "isolcpus" and they can be set individually. The other
> housekeeping types are all set by "nohz_full" without a way to set them
> individually. So they all have identical cpumasks.
> 
> There is actually no point in having different cpumasks for these
> "nohz_full" only housekeeping types. Consolidate these types to use the
> same cpumask by aliasing them to the same value. If there is a need to
> set any of them independently in the future, we can break them out to
> their own cpumasks again.
> 
> With this change, the number of cpumasks in the housekeeping structure
> drops from 9 to 4.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  include/linux/sched/isolation.h | 18 ++++++++++++------
>  kernel/sched/isolation.c        |  9 ++-------
>  2 files changed, 14 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
> index 499d5e480882..e2c42172de82 100644
> --- a/include/linux/sched/isolation.h
> +++ b/include/linux/sched/isolation.h
> @@ -7,15 +7,21 @@
>  #include <linux/tick.h>
>  
>  enum hk_type {
> -	HK_TYPE_TIMER,
> -	HK_TYPE_RCU,
> -	HK_TYPE_MISC,
>  	HK_TYPE_TICK,
>  	HK_TYPE_DOMAIN,
> -	HK_TYPE_WQ,
>  	HK_TYPE_MANAGED_IRQ,
> -	HK_TYPE_KTHREAD,
> -	HK_TYPE_MAX
> +	HK_TYPE_KERNEL_NOISE,
> +	HK_TYPE_MAX,
> +
> +	/*
> +	 * The following housekeeping types are only set by the nohz_full
> +	 * boot commandline option. So they can share the same value.
> +	 */
> +	HK_TYPE_TIMER   = HK_TYPE_KERNEL_NOISE,
> +	HK_TYPE_RCU     = HK_TYPE_KERNEL_NOISE,
> +	HK_TYPE_MISC    = HK_TYPE_KERNEL_NOISE,
> +	HK_TYPE_WQ      = HK_TYPE_KERNEL_NOISE,
> +	HK_TYPE_KTHREAD = HK_TYPE_KERNEL_NOISE
>  };
>  
>  #ifdef CONFIG_CPU_ISOLATION
> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
> index 5345e11f3d44..2b654272edcd 100644
> --- a/kernel/sched/isolation.c
> +++ b/kernel/sched/isolation.c
> @@ -9,14 +9,10 @@
>   */
>  
>  enum hk_flags {
> -	HK_FLAG_TIMER		= BIT(HK_TYPE_TIMER),
> -	HK_FLAG_RCU		= BIT(HK_TYPE_RCU),
> -	HK_FLAG_MISC		= BIT(HK_TYPE_MISC),
>  	HK_FLAG_TICK		= BIT(HK_TYPE_TICK),
>  	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
> -	HK_FLAG_WQ		= BIT(HK_TYPE_WQ),
>  	HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
> -	HK_FLAG_KTHREAD		= BIT(HK_TYPE_KTHREAD),
> +	HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
>  };
>  
>  DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
> @@ -194,8 +190,7 @@ static int __init housekeeping_nohz_full_setup(char *str)
>  {
>  	unsigned long flags;
>  
> -	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> -		HK_FLAG_MISC | HK_FLAG_KTHREAD;
> +	flags = HK_FLAG_KERNEL_NOISE;
>

This does not look equivalent. HK_FLAG_TICK seems to be lost?




Cheers,
Phil


>  	return housekeeping_setup(str, flags);
>  }
> -- 
> 2.43.5
> 

-- 

Re: [PATCH v2 2/2] sched/isolation: Consolidate housekeeping cpumasks that are always identical

[Waiman Long]

On 9/4/24 13:19, Phil Auld wrote:
> On Wed, Sep 04, 2024 at 01:14:41PM -0400 Waiman Long wrote:
>> The housekeeping cpumasks are only set by two boot commandline
>> parameters: "nohz_full" and "isolcpus". When there is more than one of
>> "nohz_full" or "isolcpus", the extra ones must have the same CPU list
>> or the setup will fail partially.
>>
>> The HK_TYPE_TICK, HK_TYPE_DOMAIN and HK_TYPE_MANAGED_IRQ types are
>> settable by "isolcpus" and they can be set individually. The other
>> housekeeping types are all set by "nohz_full" without a way to set them
>> individually. So they all have identical cpumasks.
>>
>> There is actually no point in having different cpumasks for these
>> "nohz_full" only housekeeping types. Consolidate these types to use the
>> same cpumask by aliasing them to the same value. If there is a need to
>> set any of them independently in the future, we can break them out to
>> their own cpumasks again.
>>
>> With this change, the number of cpumasks in the housekeeping structure
>> drops from 9 to 4.
>>
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   include/linux/sched/isolation.h | 18 ++++++++++++------
>>   kernel/sched/isolation.c        |  9 ++-------
>>   2 files changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/sched/isolation.h b/include/linux/sched/isolation.h
>> index 499d5e480882..e2c42172de82 100644
>> --- a/include/linux/sched/isolation.h
>> +++ b/include/linux/sched/isolation.h
>> @@ -7,15 +7,21 @@
>>   #include <linux/tick.h>
>>   
>>   enum hk_type {
>> -	HK_TYPE_TIMER,
>> -	HK_TYPE_RCU,
>> -	HK_TYPE_MISC,
>>   	HK_TYPE_TICK,
>>   	HK_TYPE_DOMAIN,
>> -	HK_TYPE_WQ,
>>   	HK_TYPE_MANAGED_IRQ,
>> -	HK_TYPE_KTHREAD,
>> -	HK_TYPE_MAX
>> +	HK_TYPE_KERNEL_NOISE,
>> +	HK_TYPE_MAX,
>> +
>> +	/*
>> +	 * The following housekeeping types are only set by the nohz_full
>> +	 * boot commandline option. So they can share the same value.
>> +	 */
>> +	HK_TYPE_TIMER   = HK_TYPE_KERNEL_NOISE,
>> +	HK_TYPE_RCU     = HK_TYPE_KERNEL_NOISE,
>> +	HK_TYPE_MISC    = HK_TYPE_KERNEL_NOISE,
>> +	HK_TYPE_WQ      = HK_TYPE_KERNEL_NOISE,
>> +	HK_TYPE_KTHREAD = HK_TYPE_KERNEL_NOISE
>>   };
>>   
>>   #ifdef CONFIG_CPU_ISOLATION
>> diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
>> index 5345e11f3d44..2b654272edcd 100644
>> --- a/kernel/sched/isolation.c
>> +++ b/kernel/sched/isolation.c
>> @@ -9,14 +9,10 @@
>>    */
>>   
>>   enum hk_flags {
>> -	HK_FLAG_TIMER		= BIT(HK_TYPE_TIMER),
>> -	HK_FLAG_RCU		= BIT(HK_TYPE_RCU),
>> -	HK_FLAG_MISC		= BIT(HK_TYPE_MISC),
>>   	HK_FLAG_TICK		= BIT(HK_TYPE_TICK),
>>   	HK_FLAG_DOMAIN		= BIT(HK_TYPE_DOMAIN),
>> -	HK_FLAG_WQ		= BIT(HK_TYPE_WQ),
>>   	HK_FLAG_MANAGED_IRQ	= BIT(HK_TYPE_MANAGED_IRQ),
>> -	HK_FLAG_KTHREAD		= BIT(HK_TYPE_KTHREAD),
>> +	HK_FLAG_KERNEL_NOISE	= BIT(HK_TYPE_KERNEL_NOISE),
>>   };
>>   
>>   DEFINE_STATIC_KEY_FALSE(housekeeping_overridden);
>> @@ -194,8 +190,7 @@ static int __init housekeeping_nohz_full_setup(char *str)
>>   {
>>   	unsigned long flags;
>>   
>> -	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
>> -		HK_FLAG_MISC | HK_FLAG_KTHREAD;
>> +	flags = HK_FLAG_KERNEL_NOISE;
>>
> This does not look equivalent. HK_FLAG_TICK seems to be lost?

You are right. I will send out v3 to correct that.

Cheers,
Longman