diff mbox series

[bpf-next,v3] bpf: Initialize same number of free nodes for each pcpu_freelist

Message ID 20221110035039.54859-1-xukuohai@huawei.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series [bpf-next,v3] bpf: Initialize same number of free nodes for each pcpu_freelist | expand

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Commit Message

Xu Kuohai Nov. 10, 2022, 3:50 a.m. UTC 
pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1
free nodes for some CPUs, and then possibly one CPU with fewer nodes,
followed by remaining cpus with 0 nodes. For example, when nr_elems == 256
and num_possible_cpus() == 32, CPU 0~27 each gets 9 free nodes, CPU 28 gets
4 free nodes, CPU 29~31 get 0 free nodes, while in fact each CPU should get
8 nodes equally.

This patch initializes nr_elems / num_possible_cpus() free nodes for each
CPU firstly, then allocates the remaining free nodes by one for each CPU
until no free nodes left.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
---
v3: Simplify code as suggested by Andrii
v2: Update commit message and add Yonghong's ack
---
 kernel/bpf/percpu_freelist.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

Comments

Andrii Nakryiko Nov. 10, 2022, 4:05 a.m. UTC | #1 
On Wed, Nov 9, 2022 at 7:33 PM Xu Kuohai <xukuohai@huawei.com> wrote:
>
> pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1
> free nodes for some CPUs, and then possibly one CPU with fewer nodes,
> followed by remaining cpus with 0 nodes. For example, when nr_elems == 256
> and num_possible_cpus() == 32, CPU 0~27 each gets 9 free nodes, CPU 28 gets
> 4 free nodes, CPU 29~31 get 0 free nodes, while in fact each CPU should get
> 8 nodes equally.
>
> This patch initializes nr_elems / num_possible_cpus() free nodes for each
> CPU firstly, then allocates the remaining free nodes by one for each CPU
> until no free nodes left.
>
> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
> Acked-by: Yonghong Song <yhs@fb.com>
> ---
> v3: Simplify code as suggested by Andrii
> v2: Update commit message and add Yonghong's ack
> ---
>  kernel/bpf/percpu_freelist.c | 27 ++++++++++++++-------------
>  1 file changed, 14 insertions(+), 13 deletions(-)
>
> diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
> index b6e7f5c5b9ab..bd60070c079f 100644
> --- a/kernel/bpf/percpu_freelist.c
> +++ b/kernel/bpf/percpu_freelist.c
> @@ -100,22 +100,23 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
>                             u32 nr_elems)
>  {
>         struct pcpu_freelist_head *head;
> -       int i, cpu, pcpu_entries;
> +       unsigned int cpu, cpu_idx, i, j, n, m;
>
> -       pcpu_entries = nr_elems / num_possible_cpus() + 1;
> -       i = 0;
> +       n = nr_elems / num_possible_cpus();
> +       m = nr_elems % num_possible_cpus();
> +
> +       cpu_idx = 0;
>
>         for_each_possible_cpu(cpu) {
> -again:
> -               head = per_cpu_ptr(s->freelist, cpu);
> -               /* No locking required as this is not visible yet. */
> -               pcpu_freelist_push_node(head, buf);
> -               i++;
> -               buf += elem_size;
> -               if (i == nr_elems)
> -                       break;
> -               if (i % pcpu_entries)
> -                       goto again;
> +               j = min(n + (cpu_idx < m ? 1 : 0), nr_elems);

why the min() here?

> +               for (i = 0; i < j; i++) {
> +                       head = per_cpu_ptr(s->freelist, cpu);
> +                       /* No locking required as this is not visible yet. */
> +                       pcpu_freelist_push_node(head, buf);
> +                       buf += elem_size;
> +               }
> +               nr_elems -= j;
> +               cpu_idx++;
>         }
>  }
>
> --
> 2.30.2
>
Xu Kuohai Nov. 10, 2022, 6:23 a.m. UTC | #2 
On 11/10/2022 12:05 PM, Andrii Nakryiko wrote:
> On Wed, Nov 9, 2022 at 7:33 PM Xu Kuohai <xukuohai@huawei.com> wrote:
>>
>> pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1
>> free nodes for some CPUs, and then possibly one CPU with fewer nodes,
>> followed by remaining cpus with 0 nodes. For example, when nr_elems == 256
>> and num_possible_cpus() == 32, CPU 0~27 each gets 9 free nodes, CPU 28 gets
>> 4 free nodes, CPU 29~31 get 0 free nodes, while in fact each CPU should get
>> 8 nodes equally.
>>
>> This patch initializes nr_elems / num_possible_cpus() free nodes for each
>> CPU firstly, then allocates the remaining free nodes by one for each CPU
>> until no free nodes left.
>>
>> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
>> Acked-by: Yonghong Song <yhs@fb.com>
>> ---
>> v3: Simplify code as suggested by Andrii
>> v2: Update commit message and add Yonghong's ack
>> ---
>>   kernel/bpf/percpu_freelist.c | 27 ++++++++++++++-------------
>>   1 file changed, 14 insertions(+), 13 deletions(-)
>>
>> diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
>> index b6e7f5c5b9ab..bd60070c079f 100644
>> --- a/kernel/bpf/percpu_freelist.c
>> +++ b/kernel/bpf/percpu_freelist.c
>> @@ -100,22 +100,23 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
>>                              u32 nr_elems)
>>   {
>>          struct pcpu_freelist_head *head;
>> -       int i, cpu, pcpu_entries;
>> +       unsigned int cpu, cpu_idx, i, j, n, m;
>>
>> -       pcpu_entries = nr_elems / num_possible_cpus() + 1;
>> -       i = 0;
>> +       n = nr_elems / num_possible_cpus();
>> +       m = nr_elems % num_possible_cpus();
>> +
>> +       cpu_idx = 0;
>>
>>          for_each_possible_cpu(cpu) {
>> -again:
>> -               head = per_cpu_ptr(s->freelist, cpu);
>> -               /* No locking required as this is not visible yet. */
>> -               pcpu_freelist_push_node(head, buf);
>> -               i++;
>> -               buf += elem_size;
>> -               if (i == nr_elems)
>> -                       break;
>> -               if (i % pcpu_entries)
>> -                       goto again;
>> +               j = min(n + (cpu_idx < m ? 1 : 0), nr_elems);
> 
> why the min() here?
> 

to avoid out-of-bounds in case nr_elems is less than the total number of CPUs,
seems not very necessary, but the original code avoids this as well, I just kept
the logic

>> +               for (i = 0; i < j; i++) {
>> +                       head = per_cpu_ptr(s->freelist, cpu);
>> +                       /* No locking required as this is not visible yet. */
>> +                       pcpu_freelist_push_node(head, buf);
>> +                       buf += elem_size;
>> +               }
>> +               nr_elems -= j;
>> +               cpu_idx++;
>>          }
>>   }
>>
>> --
>> 2.30.2
>>
> .
Xu Kuohai Nov. 10, 2022, 11:39 a.m. UTC | #3 
On 11/10/2022 2:23 PM, Xu Kuohai wrote:
> On 11/10/2022 12:05 PM, Andrii Nakryiko wrote:
>> On Wed, Nov 9, 2022 at 7:33 PM Xu Kuohai <xukuohai@huawei.com> wrote:
>>>
>>> pcpu_freelist_populate() initializes nr_elems / num_possible_cpus() + 1
>>> free nodes for some CPUs, and then possibly one CPU with fewer nodes,
>>> followed by remaining cpus with 0 nodes. For example, when nr_elems == 256
>>> and num_possible_cpus() == 32, CPU 0~27 each gets 9 free nodes, CPU 28 gets
>>> 4 free nodes, CPU 29~31 get 0 free nodes, while in fact each CPU should get
>>> 8 nodes equally.
>>>
>>> This patch initializes nr_elems / num_possible_cpus() free nodes for each
>>> CPU firstly, then allocates the remaining free nodes by one for each CPU
>>> until no free nodes left.
>>>
>>> Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
>>> Acked-by: Yonghong Song <yhs@fb.com>
>>> ---
>>> v3: Simplify code as suggested by Andrii
>>> v2: Update commit message and add Yonghong's ack
>>> ---
>>>   kernel/bpf/percpu_freelist.c | 27 ++++++++++++++-------------
>>>   1 file changed, 14 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
>>> index b6e7f5c5b9ab..bd60070c079f 100644
>>> --- a/kernel/bpf/percpu_freelist.c
>>> +++ b/kernel/bpf/percpu_freelist.c
>>> @@ -100,22 +100,23 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
>>>                              u32 nr_elems)
>>>   {
>>>          struct pcpu_freelist_head *head;
>>> -       int i, cpu, pcpu_entries;
>>> +       unsigned int cpu, cpu_idx, i, j, n, m;
>>>
>>> -       pcpu_entries = nr_elems / num_possible_cpus() + 1;
>>> -       i = 0;
>>> +       n = nr_elems / num_possible_cpus();
>>> +       m = nr_elems % num_possible_cpus();
>>> +
>>> +       cpu_idx = 0;
>>>
>>>          for_each_possible_cpu(cpu) {
>>> -again:
>>> -               head = per_cpu_ptr(s->freelist, cpu);
>>> -               /* No locking required as this is not visible yet. */
>>> -               pcpu_freelist_push_node(head, buf);
>>> -               i++;
>>> -               buf += elem_size;
>>> -               if (i == nr_elems)
>>> -                       break;
>>> -               if (i % pcpu_entries)
>>> -                       goto again;
>>> +               j = min(n + (cpu_idx < m ? 1 : 0), nr_elems);
>>
>> why the min() here?
>>
> 
> to avoid out-of-bounds in case nr_elems is less than the total number of CPUs,
> seems not very necessary, but the original code avoids this as well, I just kept
> the logic
> 

sorry, no out-of-bounds here, when nr_elems is less than the total number of CPUs,
j will be 0 when cpu_idx >= m, will post v4

>>> +               for (i = 0; i < j; i++) {
>>> +                       head = per_cpu_ptr(s->freelist, cpu);
>>> +                       /* No locking required as this is not visible yet. */
>>> +                       pcpu_freelist_push_node(head, buf);
>>> +                       buf += elem_size;
>>> +               }
>>> +               nr_elems -= j;
>>> +               cpu_idx++;
>>>          }
>>>   }
>>>
>>> -- 
>>> 2.30.2
>>>
>> .
> 
> 
> .
diff mbox series

Patch

diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
index b6e7f5c5b9ab..bd60070c079f 100644
--- a/kernel/bpf/percpu_freelist.c
+++ b/kernel/bpf/percpu_freelist.c
@@ -100,22 +100,23 @@  void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 			    u32 nr_elems)
 {
 	struct pcpu_freelist_head *head;
-	int i, cpu, pcpu_entries;
+	unsigned int cpu, cpu_idx, i, j, n, m;
 
-	pcpu_entries = nr_elems / num_possible_cpus() + 1;
-	i = 0;
+	n = nr_elems / num_possible_cpus();
+	m = nr_elems % num_possible_cpus();
+
+	cpu_idx = 0;
 
 	for_each_possible_cpu(cpu) {
-again:
-		head = per_cpu_ptr(s->freelist, cpu);
-		/* No locking required as this is not visible yet. */
-		pcpu_freelist_push_node(head, buf);
-		i++;
-		buf += elem_size;
-		if (i == nr_elems)
-			break;
-		if (i % pcpu_entries)
-			goto again;
+		j = min(n + (cpu_idx < m ? 1 : 0), nr_elems);
+		for (i = 0; i < j; i++) {
+			head = per_cpu_ptr(s->freelist, cpu);
+			/* No locking required as this is not visible yet. */
+			pcpu_freelist_push_node(head, buf);
+			buf += elem_size;
+		}
+		nr_elems -= j;
+		cpu_idx++;
 	}
 }