[v3,3/7] padata: dispatch works on different nodes

  When a group of tasks that access different nodes are scheduled on the
same node, they may encounter bandwidth bottlenecks and access latency.

Thus, numa_aware flag is introduced here, allowing tasks to be
distributed across different nodes to fully utilize the advantage of
multi-node systems.

Signed-off-by: Gang Li <gang.li@linux.dev>
---
 include/linux/padata.h | 3 +++
 kernel/padata.c        | 8 ++++++--
 mm/mm_init.c           | 1 +
 3 files changed, 10 insertions(+), 2 deletions(-)
  

On Tue, 2024-01-02 at 21:12 +0800, Gang Li wrote:
> When a group of tasks that access different nodes are scheduled on the
> same node, they may encounter bandwidth bottlenecks and access latency.
> 
> Thus, numa_aware flag is introduced here, allowing tasks to be
> distributed across different nodes to fully utilize the advantage of
> multi-node systems.
> 
> Signed-off-by: Gang Li <gang.li@linux.dev>
> ---
>  include/linux/padata.h | 3 +++
>  kernel/padata.c        | 8 ++++++--
>  mm/mm_init.c           | 1 +
>  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/padata.h b/include/linux/padata.h
> index 495b16b6b4d72..f79ccd50e7f40 100644
> --- a/include/linux/padata.h
> +++ b/include/linux/padata.h
> @@ -137,6 +137,8 @@ struct padata_shell {
>   *             appropriate for one worker thread to do at once.
>   * @max_threads: Max threads to use for the job, actual number may be less
>   *               depending on task size and minimum chunk size.
> + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
> + *              no CPU, dispatch its jobs to a random CPU.
>   */
>  struct padata_mt_job {
>  	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
> @@ -146,6 +148,7 @@ struct padata_mt_job {
>  	unsigned long		align;
>  	unsigned long		min_chunk;
>  	int			max_threads;
> +	bool			numa_aware;
>  };
>  
>  /**
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 179fb1518070c..1c2b3a337479e 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -485,7 +485,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>  	struct padata_work my_work, *pw;
>  	struct padata_mt_job_state ps;
>  	LIST_HEAD(works);
> -	int nworks;
> +	int nworks, nid = 0;

If we always start from 0, we may be biased towards the low numbered node,
and not use high numbered nodes at all.  Suggest you do
static nid = 0;  

>  
>  	if (job->size == 0)
>  		return;
> @@ -517,7 +517,11 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>  	ps.chunk_size = roundup(ps.chunk_size, job->align);
>  
>  	list_for_each_entry(pw, &works, pw_list)
> -		queue_work(system_unbound_wq, &pw->pw_work);
> +		if (job->numa_aware)
> +			queue_work_node((++nid % num_node_state(N_MEMORY)),
> +					system_unbound_wq, &pw->pw_work);

I think we should use nid = next_node(nid, node_states[N_CPU]) instead of
++nid % num_node_state(N_MEMORY).  You are picking the next node with CPU
to handle the job.

Tim

> +		else
> +			queue_work(system_unbound_wq, &pw->pw_work);
>  
>  	/* Use the current thread, which saves starting a workqueue worker. */
>  	padata_work_init(&my_work, padata_mt_helper, &ps, PADATA_WORK_ONSTACK);
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index 89dc29f1e6c6f..59fcffddf65a3 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2225,6 +2225,7 @@ static int __init deferred_init_memmap(void *data)
>  			.align       = PAGES_PER_SECTION,
>  			.min_chunk   = PAGES_PER_SECTION,
>  			.max_threads = max_threads,
> +			.numa_aware  = false,
>  		};
>  
>  		padata_do_multithreaded(&job);
  

On 2024/1/12 01:50, Tim Chen wrote:
> On Tue, 2024-01-02 at 21:12 +0800, Gang Li wrote:
>> When a group of tasks that access different nodes are scheduled on the
>> same node, they may encounter bandwidth bottlenecks and access latency.
>>
>> Thus, numa_aware flag is introduced here, allowing tasks to be
>> distributed across different nodes to fully utilize the advantage of
>> multi-node systems.
>>
>> Signed-off-by: Gang Li <gang.li@linux.dev>
>> ---
>>   include/linux/padata.h | 3 +++
>>   kernel/padata.c        | 8 ++++++--
>>   mm/mm_init.c           | 1 +
>>   3 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/padata.h b/include/linux/padata.h
>> index 495b16b6b4d72..f79ccd50e7f40 100644
>> --- a/include/linux/padata.h
>> +++ b/include/linux/padata.h
>> @@ -137,6 +137,8 @@ struct padata_shell {
>>    *             appropriate for one worker thread to do at once.
>>    * @max_threads: Max threads to use for the job, actual number may be less
>>    *               depending on task size and minimum chunk size.
>> + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
>> + *              no CPU, dispatch its jobs to a random CPU.
>>    */
>>   struct padata_mt_job {
>>   	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
>> @@ -146,6 +148,7 @@ struct padata_mt_job {
>>   	unsigned long		align;
>>   	unsigned long		min_chunk;
>>   	int			max_threads;
>> +	bool			numa_aware;
>>   };
>>   
>>   /**
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index 179fb1518070c..1c2b3a337479e 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -485,7 +485,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>   	struct padata_work my_work, *pw;
>>   	struct padata_mt_job_state ps;
>>   	LIST_HEAD(works);
>> -	int nworks;
>> +	int nworks, nid = 0;
> 
> If we always start from 0, we may be biased towards the low numbered node,
> and not use high numbered nodes at all.  Suggest you do
> static nid = 0;
> 

When we use `static`, if there are multiple parallel calls to
`padata_do_multithreaded`, it may result in an uneven distribution of
tasks for each padata_do_multithreaded.

We can make the following modifications to address this issue.

```
diff --git a/kernel/padata.c b/kernel/padata.c
index 1c2b3a337479e..925e48df6dd8d 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -485,7 +485,8 @@ void __init padata_do_multithreaded(struct 
padata_mt_job *job)
         struct padata_work my_work, *pw;
         struct padata_mt_job_state ps;
         LIST_HEAD(works);
-       int nworks, nid = 0;
+       int nworks, nid;
+       static volatile int global_nid = 0;

         if (job->size == 0)
                 return;
@@ -516,12 +517,15 @@ void __init padata_do_multithreaded(struct 
padata_mt_job *job)
         ps.chunk_size = max(ps.chunk_size, job->min_chunk);
         ps.chunk_size = roundup(ps.chunk_size, job->align);

+       nid = global_nid;
         list_for_each_entry(pw, &works, pw_list)
-               if (job->numa_aware)
-                       queue_work_node((++nid % num_node_state(N_MEMORY)),
-                                       system_unbound_wq, &pw->pw_work);
-               else
+               if (job->numa_aware) {
+                       queue_work_node(nid, system_unbound_wq, 
&pw->pw_work);
+                       nid = next_node(nid, node_states[N_CPU]);
+               } else
                         queue_work(system_unbound_wq, &pw->pw_work);
+       if (job->numa_aware)
+               global_nid = nid;

         /* Use the current thread, which saves starting a workqueue 
worker. */
         padata_work_init(&my_work, padata_mt_helper, &ps, 
PADATA_WORK_ONSTACK);
```


>>   
>>   	if (job->size == 0)
>>   		return;
>> @@ -517,7 +517,11 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>   	ps.chunk_size = roundup(ps.chunk_size, job->align);
>>   
>>   	list_for_each_entry(pw, &works, pw_list)
>> -		queue_work(system_unbound_wq, &pw->pw_work);
>> +		if (job->numa_aware)
>> +			queue_work_node((++nid % num_node_state(N_MEMORY)),
>> +					system_unbound_wq, &pw->pw_work);
> 
> I think we should use nid = next_node(nid, node_states[N_CPU]) instead of
> ++nid % num_node_state(N_MEMORY).  You are picking the next node with CPU
> to handle the job.
> 
> Tim
> 

I agree.
  

On Fri, 2024-01-12 at 15:09 +0800, Gang Li wrote:
> On 2024/1/12 01:50, Tim Chen wrote:
> > On Tue, 2024-01-02 at 21:12 +0800, Gang Li wrote:
> > > When a group of tasks that access different nodes are scheduled on the
> > > same node, they may encounter bandwidth bottlenecks and access latency.
> > > 
> > > Thus, numa_aware flag is introduced here, allowing tasks to be
> > > distributed across different nodes to fully utilize the advantage of
> > > multi-node systems.
> > > 
> > > Signed-off-by: Gang Li <gang.li@linux.dev>
> > > ---
> > >   include/linux/padata.h | 3 +++
> > >   kernel/padata.c        | 8 ++++++--
> > >   mm/mm_init.c           | 1 +
> > >   3 files changed, 10 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/include/linux/padata.h b/include/linux/padata.h
> > > index 495b16b6b4d72..f79ccd50e7f40 100644
> > > --- a/include/linux/padata.h
> > > +++ b/include/linux/padata.h
> > > @@ -137,6 +137,8 @@ struct padata_shell {
> > >    *             appropriate for one worker thread to do at once.
> > >    * @max_threads: Max threads to use for the job, actual number may be less
> > >    *               depending on task size and minimum chunk size.
> > > + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
> > > + *              no CPU, dispatch its jobs to a random CPU.
> > >    */
> > >   struct padata_mt_job {
> > >   	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
> > > @@ -146,6 +148,7 @@ struct padata_mt_job {
> > >   	unsigned long		align;
> > >   	unsigned long		min_chunk;
> > >   	int			max_threads;
> > > +	bool			numa_aware;
> > >   };
> > >   
> > >   /**
> > > diff --git a/kernel/padata.c b/kernel/padata.c
> > > index 179fb1518070c..1c2b3a337479e 100644
> > > --- a/kernel/padata.c
> > > +++ b/kernel/padata.c
> > > @@ -485,7 +485,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
> > >   	struct padata_work my_work, *pw;
> > >   	struct padata_mt_job_state ps;
> > >   	LIST_HEAD(works);
> > > -	int nworks;
> > > +	int nworks, nid = 0;
> > 
> > If we always start from 0, we may be biased towards the low numbered node,
> > and not use high numbered nodes at all.  Suggest you do
> > static nid = 0;
> > 
> 
> When we use `static`, if there are multiple parallel calls to
> `padata_do_multithreaded`, it may result in an uneven distribution of
> tasks for each padata_do_multithreaded.
> 
> We can make the following modifications to address this issue.
> 
> ```
> diff --git a/kernel/padata.c b/kernel/padata.c
> index 1c2b3a337479e..925e48df6dd8d 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -485,7 +485,8 @@ void __init padata_do_multithreaded(struct 
> padata_mt_job *job)
>          struct padata_work my_work, *pw;
>          struct padata_mt_job_state ps;
>          LIST_HEAD(works);
> -       int nworks, nid = 0;
> +       int nworks, nid;
> +       static volatile int global_nid = 0;
> 
>          if (job->size == 0)
>                  return;
> @@ -516,12 +517,15 @@ void __init padata_do_multithreaded(struct 
> padata_mt_job *job)
>          ps.chunk_size = max(ps.chunk_size, job->min_chunk);
>          ps.chunk_size = roundup(ps.chunk_size, job->align);
> 
> +       nid = global_nid;
>          list_for_each_entry(pw, &works, pw_list)
> -               if (job->numa_aware)
> -                       queue_work_node((++nid % num_node_state(N_MEMORY)),
> -                                       system_unbound_wq, &pw->pw_work);
> -               else
> +               if (job->numa_aware) {
> +                       queue_work_node(nid, system_unbound_wq, 
> &pw->pw_work);
> +                       nid = next_node(nid, node_states[N_CPU]);
> +               } else
>                          queue_work(system_unbound_wq, &pw->pw_work);
> +       if (job->numa_aware)
> +               global_nid = nid;

Thinking more about it, there could still be multiple threads working
at the same time with stale global_nid.  We should probably do a compare
exchange of global_nid with new nid only if the global nid was unchanged.
Otherwise we should go to the next node with the changed global nid before
we queue the job.

Tim

> 
>          /* Use the current thread, which saves starting a workqueue 
> worker. */
>          padata_work_init(&my_work, padata_mt_helper, &ps, 
> PADATA_WORK_ONSTACK);
> ```
> 
> 
> > >   
> > >   	if (job->size == 0)
> > >   		return;
> > > @@ -517,7 +517,11 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
> > >   	ps.chunk_size = roundup(ps.chunk_size, job->align);
> > >   
> > >   	list_for_each_entry(pw, &works, pw_list)
> > > -		queue_work(system_unbound_wq, &pw->pw_work);
> > > +		if (job->numa_aware)
> > > +			queue_work_node((++nid % num_node_state(N_MEMORY)),
> > > +					system_unbound_wq, &pw->pw_work);
> > 
> > I think we should use nid = next_node(nid, node_states[N_CPU]) instead of
> > ++nid % num_node_state(N_MEMORY).  You are picking the next node with CPU
> > to handle the job.
> > 
> > Tim
> > 
> 
> I agree.
  

On 2024/1/13 02:27, Tim Chen wrote:
> On Fri, 2024-01-12 at 15:09 +0800, Gang Li wrote:
>> On 2024/1/12 01:50, Tim Chen wrote:
>>> On Tue, 2024-01-02 at 21:12 +0800, Gang Li wrote:
>>>> When a group of tasks that access different nodes are scheduled on the
>>>> same node, they may encounter bandwidth bottlenecks and access latency.
>>>>
>>>> Thus, numa_aware flag is introduced here, allowing tasks to be
>>>> distributed across different nodes to fully utilize the advantage of
>>>> multi-node systems.
>>>>
>>>> Signed-off-by: Gang Li <gang.li@linux.dev>
>>>> ---
>>>>    include/linux/padata.h | 3 +++
>>>>    kernel/padata.c        | 8 ++++++--
>>>>    mm/mm_init.c           | 1 +
>>>>    3 files changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/include/linux/padata.h b/include/linux/padata.h
>>>> index 495b16b6b4d72..f79ccd50e7f40 100644
>>>> --- a/include/linux/padata.h
>>>> +++ b/include/linux/padata.h
>>>> @@ -137,6 +137,8 @@ struct padata_shell {
>>>>     *             appropriate for one worker thread to do at once.
>>>>     * @max_threads: Max threads to use for the job, actual number may be less
>>>>     *               depending on task size and minimum chunk size.
>>>> + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
>>>> + *              no CPU, dispatch its jobs to a random CPU.
>>>>     */
>>>>    struct padata_mt_job {
>>>>    	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
>>>> @@ -146,6 +148,7 @@ struct padata_mt_job {
>>>>    	unsigned long		align;
>>>>    	unsigned long		min_chunk;
>>>>    	int			max_threads;
>>>> +	bool			numa_aware;
>>>>    };
>>>>    
>>>>    /**
>>>> diff --git a/kernel/padata.c b/kernel/padata.c
>>>> index 179fb1518070c..1c2b3a337479e 100644
>>>> --- a/kernel/padata.c
>>>> +++ b/kernel/padata.c
>>>> @@ -485,7 +485,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>>>>    	struct padata_work my_work, *pw;
>>>>    	struct padata_mt_job_state ps;
>>>>    	LIST_HEAD(works);
>>>> -	int nworks;
>>>> +	int nworks, nid = 0;
>>>
>>> If we always start from 0, we may be biased towards the low numbered node,
>>> and not use high numbered nodes at all.  Suggest you do
>>> static nid = 0;
>>>
>>
>> When we use `static`, if there are multiple parallel calls to
>> `padata_do_multithreaded`, it may result in an uneven distribution of
>> tasks for each padata_do_multithreaded.
>>
>> We can make the following modifications to address this issue.
>>
>> ```
>> diff --git a/kernel/padata.c b/kernel/padata.c
>> index 1c2b3a337479e..925e48df6dd8d 100644
>> --- a/kernel/padata.c
>> +++ b/kernel/padata.c
>> @@ -485,7 +485,8 @@ void __init padata_do_multithreaded(struct
>> padata_mt_job *job)
>>           struct padata_work my_work, *pw;
>>           struct padata_mt_job_state ps;
>>           LIST_HEAD(works);
>> -       int nworks, nid = 0;
>> +       int nworks, nid;
>> +       static volatile int global_nid = 0;
>>
>>           if (job->size == 0)
>>                   return;
>> @@ -516,12 +517,15 @@ void __init padata_do_multithreaded(struct
>> padata_mt_job *job)
>>           ps.chunk_size = max(ps.chunk_size, job->min_chunk);
>>           ps.chunk_size = roundup(ps.chunk_size, job->align);
>>
>> +       nid = global_nid;
>>           list_for_each_entry(pw, &works, pw_list)
>> -               if (job->numa_aware)
>> -                       queue_work_node((++nid % num_node_state(N_MEMORY)),
>> -                                       system_unbound_wq, &pw->pw_work);
>> -               else
>> +               if (job->numa_aware) {
>> +                       queue_work_node(nid, system_unbound_wq,
>> &pw->pw_work);
>> +                       nid = next_node(nid, node_states[N_CPU]);
>> +               } else
>>                           queue_work(system_unbound_wq, &pw->pw_work);
>> +       if (job->numa_aware)
>> +               global_nid = nid;
> 
> Thinking more about it, there could still be multiple threads working
> at the same time with stale global_nid.  We should probably do a compare
> exchange of global_nid with new nid only if the global nid was unchanged.
> Otherwise we should go to the next node with the changed global nid before
> we queue the job.
> 
> Tim
> 
How about:
```
nid = global_nid;
list_for_each_entry(pw, &works, pw_list)
	if (job->numa_aware) {
		int old_node = nid;
		queue_work_node(nid, system_unbound_wq, &pw->pw_work);
		nid = next_node(nid, node_states[N_CPU]);
		cmpxchg(&global_nid, old_node, nid);
	} else
		queue_work(system_unbound_wq, &pw->pw_work);

```
  

On Mon, 2024-01-15 at 16:57 +0800, Gang Li wrote:
> 
> On 2024/1/13 02:27, Tim Chen wrote:
> > On Fri, 2024-01-12 at 15:09 +0800, Gang Li wrote:
> > > On 2024/1/12 01:50, Tim Chen wrote:
> > > > On Tue, 2024-01-02 at 21:12 +0800, Gang Li wrote:
> > > > > When a group of tasks that access different nodes are scheduled on the
> > > > > same node, they may encounter bandwidth bottlenecks and access latency.
> > > > > 
> > > > > Thus, numa_aware flag is introduced here, allowing tasks to be
> > > > > distributed across different nodes to fully utilize the advantage of
> > > > > multi-node systems.
> > > > > 
> > > > > Signed-off-by: Gang Li <gang.li@linux.dev>
> > > > > ---
> > > > >    include/linux/padata.h | 3 +++
> > > > >    kernel/padata.c        | 8 ++++++--
> > > > >    mm/mm_init.c           | 1 +
> > > > >    3 files changed, 10 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/include/linux/padata.h b/include/linux/padata.h
> > > > > index 495b16b6b4d72..f79ccd50e7f40 100644
> > > > > --- a/include/linux/padata.h
> > > > > +++ b/include/linux/padata.h
> > > > > @@ -137,6 +137,8 @@ struct padata_shell {
> > > > >     *             appropriate for one worker thread to do at once.
> > > > >     * @max_threads: Max threads to use for the job, actual number may be less
> > > > >     *               depending on task size and minimum chunk size.
> > > > > + * @numa_aware: Dispatch jobs to different nodes. If a node only has memory but
> > > > > + *              no CPU, dispatch its jobs to a random CPU.
> > > > >     */
> > > > >    struct padata_mt_job {
> > > > >    	void (*thread_fn)(unsigned long start, unsigned long end, void *arg);
> > > > > @@ -146,6 +148,7 @@ struct padata_mt_job {
> > > > >    	unsigned long		align;
> > > > >    	unsigned long		min_chunk;
> > > > >    	int			max_threads;
> > > > > +	bool			numa_aware;
> > > > >    };
> > > > >    
> > > > >    /**
> > > > > diff --git a/kernel/padata.c b/kernel/padata.c
> > > > > index 179fb1518070c..1c2b3a337479e 100644
> > > > > --- a/kernel/padata.c
> > > > > +++ b/kernel/padata.c
> > > > > @@ -485,7 +485,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
> > > > >    	struct padata_work my_work, *pw;
> > > > >    	struct padata_mt_job_state ps;
> > > > >    	LIST_HEAD(works);
> > > > > -	int nworks;
> > > > > +	int nworks, nid = 0;
> > > > 
> > > > If we always start from 0, we may be biased towards the low numbered node,
> > > > and not use high numbered nodes at all.  Suggest you do
> > > > static nid = 0;
> > > > 
> > > 
> > > When we use `static`, if there are multiple parallel calls to
> > > `padata_do_multithreaded`, it may result in an uneven distribution of
> > > tasks for each padata_do_multithreaded.
> > > 
> > > We can make the following modifications to address this issue.
> > > 
> > > ```
> > > diff --git a/kernel/padata.c b/kernel/padata.c
> > > index 1c2b3a337479e..925e48df6dd8d 100644
> > > --- a/kernel/padata.c
> > > +++ b/kernel/padata.c
> > > @@ -485,7 +485,8 @@ void __init padata_do_multithreaded(struct
> > > padata_mt_job *job)
> > >           struct padata_work my_work, *pw;
> > >           struct padata_mt_job_state ps;
> > >           LIST_HEAD(works);
> > > -       int nworks, nid = 0;
> > > +       int nworks, nid;
> > > +       static volatile int global_nid = 0;
> > > 
> > >           if (job->size == 0)
> > >                   return;
> > > @@ -516,12 +517,15 @@ void __init padata_do_multithreaded(struct
> > > padata_mt_job *job)
> > >           ps.chunk_size = max(ps.chunk_size, job->min_chunk);
> > >           ps.chunk_size = roundup(ps.chunk_size, job->align);
> > > 
> > > +       nid = global_nid;
> > >           list_for_each_entry(pw, &works, pw_list)
> > > -               if (job->numa_aware)
> > > -                       queue_work_node((++nid % num_node_state(N_MEMORY)),
> > > -                                       system_unbound_wq, &pw->pw_work);
> > > -               else
> > > +               if (job->numa_aware) {
> > > +                       queue_work_node(nid, system_unbound_wq,
> > > &pw->pw_work);
> > > +                       nid = next_node(nid, node_states[N_CPU]);
> > > +               } else
> > >                           queue_work(system_unbound_wq, &pw->pw_work);
> > > +       if (job->numa_aware)
> > > +               global_nid = nid;
> > 
> > Thinking more about it, there could still be multiple threads working
> > at the same time with stale global_nid.  We should probably do a compare
> > exchange of global_nid with new nid only if the global nid was unchanged.
> > Otherwise we should go to the next node with the changed global nid before
> > we queue the job.
> > 
> > Tim
> > 
> How about:
> ```
> nid = global_nid;
> list_for_each_entry(pw, &works, pw_list)
> 	if (job->numa_aware) {
> 		int old_node = nid;
> 		queue_work_node(nid, system_unbound_wq, &pw->pw_work);
> 		nid = next_node(nid, node_states[N_CPU]);
> 		cmpxchg(&global_nid, old_node, nid);
> 	} else
> 		queue_work(system_unbound_wq, &pw->pw_work);
> 
> ```
> 

I am thinking something like

static volatile atomic_t last_used_nid;

list_for_each_entry(pw, &works, pw_list)
 	if (job->numa_aware) {
		int old_node = atomic_read(&last_used_nid);
		
		do {
			nid = next_node_in(old_node, node_states[N_CPU]);
		} while (!atomic_try_cmpxchg(&last_used_nid, &old_node, nid));
 		queue_work_node(nid, system_unbound_wq, &pw->pw_work);		
 	} else {
 		queue_work(system_unbound_wq, &pw->pw_work);
	}

Note that we need to use next_node_in so we'll wrap around the node mask.

Tim
  

Hi Tim,

On 2024/1/18 06:14, Tim Chen wrote:
> On Mon, 2024-01-15 at 16:57 +0800, Gang Li wrote:
>> How about:
>> ```
>> nid = global_nid;
>> list_for_each_entry(pw, &works, pw_list)
>> 	if (job->numa_aware) {
>> 		int old_node = nid;
>> 		queue_work_node(nid, system_unbound_wq, &pw->pw_work);
>> 		nid = next_node(nid, node_states[N_CPU]);
>> 		cmpxchg(&global_nid, old_node, nid);



>> 	} else
>> 		queue_work(system_unbound_wq, &pw->pw_work);
>>
>> ```
>>

My original idea was to have all tasks from a single
padata_do_multithreaded distributed continuously across NUMA nodes.

In that case, the task distribution would be predictable for a single
padata_do_multithreaded call.

> 
> I am thinking something like
> 
> static volatile atomic_t last_used_nid;
> 
> list_for_each_entry(pw, &works, pw_list)
>   	if (job->numa_aware) {
> 		int old_node = atomic_read(&last_used_nid);
> 		
> 		do {
> 			nid = next_node_in(old_node, node_states[N_CPU]);
> 		} while (!atomic_try_cmpxchg(&last_used_nid, &old_node, nid));


However, having the tasks from all parallel padata_do_multithreaded
globally distributed across NUMA nodes is also fine by me.

I don't have a strong preference.

>   		queue_work_node(nid, system_unbound_wq, &pw->pw_work);		
>   	} else {
>   		queue_work(system_unbound_wq, &pw->pw_work);
> 	}
> 
> Note that we need to use next_node_in so we'll wrap around the node mask.
>