diff mbox series

[v3,1/2] bpf: avoid grabbing spin_locks of all cpus when no free elems

Message ID 20220530091340.53443-2-zhoufeng.zf@bytedance.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series Optimize performance of update hash-map when free is zero | expand

Checks

Context Check Description
bpf/vmtest-bpf-next-VM_Test-1 success Logs for Kernel LATEST on ubuntu-latest with gcc
bpf/vmtest-bpf-next-VM_Test-2 success Logs for Kernel LATEST on ubuntu-latest with llvm-15
bpf/vmtest-bpf-next-PR success PR summary
bpf/vmtest-bpf-next-VM_Test-3 success Logs for Kernel LATEST on z15 with gcc
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 13 this patch: 13
netdev/cc_maintainers success CCed 10 of 10 maintainers
netdev/build_clang success Errors and warnings before: 7 this patch: 7
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 13 this patch: 13
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 97 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/tree_selection success Guessing tree name failed - patch did not apply

Commit Message

Feng Zhou May 30, 2022, 9:13 a.m. UTC 
From: Feng Zhou <zhoufeng.zf@bytedance.com>

This patch add is_empty in pcpu_freelist_head to check freelist
having free or not. If having, grab spin_lock, or check next cpu's
freelist.

Before patch: hash_map performance
./map_perf_test 1
0:hash_map_perf pre-alloc 975345 events per sec
4:hash_map_perf pre-alloc 855367 events per sec
12:hash_map_perf pre-alloc 860862 events per sec
8:hash_map_perf pre-alloc 849561 events per sec
3:hash_map_perf pre-alloc 849074 events per sec
6:hash_map_perf pre-alloc 847120 events per sec
10:hash_map_perf pre-alloc 845047 events per sec
5:hash_map_perf pre-alloc 841266 events per sec
14:hash_map_perf pre-alloc 849740 events per sec
2:hash_map_perf pre-alloc 839598 events per sec
9:hash_map_perf pre-alloc 838695 events per sec
11:hash_map_perf pre-alloc 845390 events per sec
7:hash_map_perf pre-alloc 834865 events per sec
13:hash_map_perf pre-alloc 842619 events per sec
1:hash_map_perf pre-alloc 804231 events per sec
15:hash_map_perf pre-alloc 795314 events per sec

hash_map the worst: no free
./map_perf_test 2048
6:worse hash_map_perf pre-alloc 28628 events per sec
5:worse hash_map_perf pre-alloc 28553 events per sec
11:worse hash_map_perf pre-alloc 28543 events per sec
3:worse hash_map_perf pre-alloc 28444 events per sec
1:worse hash_map_perf pre-alloc 28418 events per sec
7:worse hash_map_perf pre-alloc 28427 events per sec
13:worse hash_map_perf pre-alloc 28330 events per sec
14:worse hash_map_perf pre-alloc 28263 events per sec
9:worse hash_map_perf pre-alloc 28211 events per sec
15:worse hash_map_perf pre-alloc 28193 events per sec
12:worse hash_map_perf pre-alloc 28190 events per sec
10:worse hash_map_perf pre-alloc 28129 events per sec
8:worse hash_map_perf pre-alloc 28116 events per sec
4:worse hash_map_perf pre-alloc 27906 events per sec
2:worse hash_map_perf pre-alloc 27801 events per sec
0:worse hash_map_perf pre-alloc 27416 events per sec
3:worse hash_map_perf pre-alloc 28188 events per sec

ftrace trace

0)               |  htab_map_update_elem() {
0)   0.198 us    |    migrate_disable();
0)               |    _raw_spin_lock_irqsave() {
0)   0.157 us    |      preempt_count_add();
0)   0.538 us    |    }
0)   0.260 us    |    lookup_elem_raw();
0)               |    alloc_htab_elem() {
0)               |      __pcpu_freelist_pop() {
0)               |        _raw_spin_lock() {
0)   0.152 us    |          preempt_count_add();
0)   0.352 us    |          native_queued_spin_lock_slowpath();
0)   1.065 us    |        }
		 |	  ...
0)               |        _raw_spin_unlock() {
0)   0.254 us    |          preempt_count_sub();
0)   0.555 us    |        }
0) + 25.188 us   |      }
0) + 25.486 us   |    }
0)               |    _raw_spin_unlock_irqrestore() {
0)   0.155 us    |      preempt_count_sub();
0)   0.454 us    |    }
0)   0.148 us    |    migrate_enable();
0) + 28.439 us   |  }

The test machine is 16C, trying to get spin_lock 17 times, in addition
to 16c, there is an extralist.

after patch: hash_map performance
./map_perf_test 1
0:hash_map_perf pre-alloc 969348 events per sec
10:hash_map_perf pre-alloc 906526 events per sec
11:hash_map_perf pre-alloc 904557 events per sec
9:hash_map_perf pre-alloc 902384 events per sec
15:hash_map_perf pre-alloc 912287 events per sec
14:hash_map_perf pre-alloc 905689 events per sec
12:hash_map_perf pre-alloc 903680 events per sec
13:hash_map_perf pre-alloc 902631 events per sec
8:hash_map_perf pre-alloc 875369 events per sec
4:hash_map_perf pre-alloc 862808 events per sec
1:hash_map_perf pre-alloc 857218 events per sec
2:hash_map_perf pre-alloc 852875 events per sec
5:hash_map_perf pre-alloc 846497 events per sec
6:hash_map_perf pre-alloc 828467 events per sec
3:hash_map_perf pre-alloc 812542 events per sec
7:hash_map_perf pre-alloc 805336 events per sec

hash_map worst: no free
./map_perf_test 2048
7:worse hash_map_perf pre-alloc 391104 events per sec
4:worse hash_map_perf pre-alloc 388073 events per sec
5:worse hash_map_perf pre-alloc 387038 events per sec
1:worse hash_map_perf pre-alloc 386546 events per sec
0:worse hash_map_perf pre-alloc 384590 events per sec
11:worse hash_map_perf pre-alloc 379378 events per sec
10:worse hash_map_perf pre-alloc 375480 events per sec
12:worse hash_map_perf pre-alloc 372394 events per sec
6:worse hash_map_perf pre-alloc 367692 events per sec
3:worse hash_map_perf pre-alloc 363970 events per sec
9:worse hash_map_perf pre-alloc 364008 events per sec
8:worse hash_map_perf pre-alloc 363759 events per sec
2:worse hash_map_perf pre-alloc 360743 events per sec
14:worse hash_map_perf pre-alloc 361195 events per sec
13:worse hash_map_perf pre-alloc 360276 events per sec
15:worse hash_map_perf pre-alloc 360057 events per sec
0:worse hash_map_perf pre-alloc 378177 events per sec

ftrace trace
0)               |  htab_map_update_elem() {
0)   0.317 us    |    migrate_disable();
0)               |    _raw_spin_lock_irqsave() {
0)   0.260 us    |      preempt_count_add();
0)   1.803 us    |    }
0)   0.276 us    |    lookup_elem_raw();
0)               |    alloc_htab_elem() {
0)   0.586 us    |      __pcpu_freelist_pop();
0)   0.945 us    |    }
0)               |    _raw_spin_unlock_irqrestore() {
0)   0.160 us    |      preempt_count_sub();
0)   0.972 us    |    }
0)   0.657 us    |    migrate_enable();
0)   8.669 us    |  }

It can be seen that after adding this patch, the map performance is
almost not degraded, and when free=0, first check is_empty instead of
directly acquiring spin_lock.

As for why to add is_empty instead of directly judging head->first, my
understanding is this, head->first is frequently modified during updating
map, which will lead to invalid other cpus's cache, and is_empty is after
freelist having no free elems will be changed, the performance will be better.

Co-developed-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
---
 kernel/bpf/percpu_freelist.c | 28 +++++++++++++++++++++++++---
 kernel/bpf/percpu_freelist.h |  1 +
 2 files changed, 26 insertions(+), 3 deletions(-)

Comments

Daniel Borkmann May 30, 2022, 9:20 p.m. UTC | #1 
On 5/30/22 11:13 AM, Feng zhou wrote:
> From: Feng Zhou <zhoufeng.zf@bytedance.com>
> 
> This patch add is_empty in pcpu_freelist_head to check freelist
> having free or not. If having, grab spin_lock, or check next cpu's
> freelist.
> 
> Before patch: hash_map performance
> ./map_perf_test 1
> 0:hash_map_perf pre-alloc 975345 events per sec
> 4:hash_map_perf pre-alloc 855367 events per sec
> 12:hash_map_perf pre-alloc 860862 events per sec
> 8:hash_map_perf pre-alloc 849561 events per sec
> 3:hash_map_perf pre-alloc 849074 events per sec
> 6:hash_map_perf pre-alloc 847120 events per sec
> 10:hash_map_perf pre-alloc 845047 events per sec
> 5:hash_map_perf pre-alloc 841266 events per sec
> 14:hash_map_perf pre-alloc 849740 events per sec
> 2:hash_map_perf pre-alloc 839598 events per sec
> 9:hash_map_perf pre-alloc 838695 events per sec
> 11:hash_map_perf pre-alloc 845390 events per sec
> 7:hash_map_perf pre-alloc 834865 events per sec
> 13:hash_map_perf pre-alloc 842619 events per sec
> 1:hash_map_perf pre-alloc 804231 events per sec
> 15:hash_map_perf pre-alloc 795314 events per sec
> 
> hash_map the worst: no free
> ./map_perf_test 2048
> 6:worse hash_map_perf pre-alloc 28628 events per sec
> 5:worse hash_map_perf pre-alloc 28553 events per sec
> 11:worse hash_map_perf pre-alloc 28543 events per sec
> 3:worse hash_map_perf pre-alloc 28444 events per sec
> 1:worse hash_map_perf pre-alloc 28418 events per sec
> 7:worse hash_map_perf pre-alloc 28427 events per sec
> 13:worse hash_map_perf pre-alloc 28330 events per sec
> 14:worse hash_map_perf pre-alloc 28263 events per sec
> 9:worse hash_map_perf pre-alloc 28211 events per sec
> 15:worse hash_map_perf pre-alloc 28193 events per sec
> 12:worse hash_map_perf pre-alloc 28190 events per sec
> 10:worse hash_map_perf pre-alloc 28129 events per sec
> 8:worse hash_map_perf pre-alloc 28116 events per sec
> 4:worse hash_map_perf pre-alloc 27906 events per sec
> 2:worse hash_map_perf pre-alloc 27801 events per sec
> 0:worse hash_map_perf pre-alloc 27416 events per sec
> 3:worse hash_map_perf pre-alloc 28188 events per sec
> 
> ftrace trace
> 
> 0)               |  htab_map_update_elem() {
> 0)   0.198 us    |    migrate_disable();
> 0)               |    _raw_spin_lock_irqsave() {
> 0)   0.157 us    |      preempt_count_add();
> 0)   0.538 us    |    }
> 0)   0.260 us    |    lookup_elem_raw();
> 0)               |    alloc_htab_elem() {
> 0)               |      __pcpu_freelist_pop() {
> 0)               |        _raw_spin_lock() {
> 0)   0.152 us    |          preempt_count_add();
> 0)   0.352 us    |          native_queued_spin_lock_slowpath();
> 0)   1.065 us    |        }
> 		 |	  ...
> 0)               |        _raw_spin_unlock() {
> 0)   0.254 us    |          preempt_count_sub();
> 0)   0.555 us    |        }
> 0) + 25.188 us   |      }
> 0) + 25.486 us   |    }
> 0)               |    _raw_spin_unlock_irqrestore() {
> 0)   0.155 us    |      preempt_count_sub();
> 0)   0.454 us    |    }
> 0)   0.148 us    |    migrate_enable();
> 0) + 28.439 us   |  }
> 
> The test machine is 16C, trying to get spin_lock 17 times, in addition
> to 16c, there is an extralist.
> 
> after patch: hash_map performance
> ./map_perf_test 1
> 0:hash_map_perf pre-alloc 969348 events per sec
> 10:hash_map_perf pre-alloc 906526 events per sec
> 11:hash_map_perf pre-alloc 904557 events per sec
> 9:hash_map_perf pre-alloc 902384 events per sec
> 15:hash_map_perf pre-alloc 912287 events per sec
> 14:hash_map_perf pre-alloc 905689 events per sec
> 12:hash_map_perf pre-alloc 903680 events per sec
> 13:hash_map_perf pre-alloc 902631 events per sec
> 8:hash_map_perf pre-alloc 875369 events per sec
> 4:hash_map_perf pre-alloc 862808 events per sec
> 1:hash_map_perf pre-alloc 857218 events per sec
> 2:hash_map_perf pre-alloc 852875 events per sec
> 5:hash_map_perf pre-alloc 846497 events per sec
> 6:hash_map_perf pre-alloc 828467 events per sec
> 3:hash_map_perf pre-alloc 812542 events per sec
> 7:hash_map_perf pre-alloc 805336 events per sec
> 
> hash_map worst: no free
> ./map_perf_test 2048
> 7:worse hash_map_perf pre-alloc 391104 events per sec
> 4:worse hash_map_perf pre-alloc 388073 events per sec
> 5:worse hash_map_perf pre-alloc 387038 events per sec
> 1:worse hash_map_perf pre-alloc 386546 events per sec
> 0:worse hash_map_perf pre-alloc 384590 events per sec
> 11:worse hash_map_perf pre-alloc 379378 events per sec
> 10:worse hash_map_perf pre-alloc 375480 events per sec
> 12:worse hash_map_perf pre-alloc 372394 events per sec
> 6:worse hash_map_perf pre-alloc 367692 events per sec
> 3:worse hash_map_perf pre-alloc 363970 events per sec
> 9:worse hash_map_perf pre-alloc 364008 events per sec
> 8:worse hash_map_perf pre-alloc 363759 events per sec
> 2:worse hash_map_perf pre-alloc 360743 events per sec
> 14:worse hash_map_perf pre-alloc 361195 events per sec
> 13:worse hash_map_perf pre-alloc 360276 events per sec
> 15:worse hash_map_perf pre-alloc 360057 events per sec
> 0:worse hash_map_perf pre-alloc 378177 events per sec
> 
> ftrace trace
> 0)               |  htab_map_update_elem() {
> 0)   0.317 us    |    migrate_disable();
> 0)               |    _raw_spin_lock_irqsave() {
> 0)   0.260 us    |      preempt_count_add();
> 0)   1.803 us    |    }
> 0)   0.276 us    |    lookup_elem_raw();
> 0)               |    alloc_htab_elem() {
> 0)   0.586 us    |      __pcpu_freelist_pop();
> 0)   0.945 us    |    }
> 0)               |    _raw_spin_unlock_irqrestore() {
> 0)   0.160 us    |      preempt_count_sub();
> 0)   0.972 us    |    }
> 0)   0.657 us    |    migrate_enable();
> 0)   8.669 us    |  }
> 
> It can be seen that after adding this patch, the map performance is
> almost not degraded, and when free=0, first check is_empty instead of
> directly acquiring spin_lock.
> 
> As for why to add is_empty instead of directly judging head->first, my
> understanding is this, head->first is frequently modified during updating
> map, which will lead to invalid other cpus's cache, and is_empty is after
> freelist having no free elems will be changed, the performance will be better.
> 
> Co-developed-by: Chengming Zhou <zhouchengming@bytedance.com>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
> ---
>   kernel/bpf/percpu_freelist.c | 28 +++++++++++++++++++++++++---
>   kernel/bpf/percpu_freelist.h |  1 +
>   2 files changed, 26 insertions(+), 3 deletions(-)
[...]
>   	/* per cpu lists are all empty, try extralist */
> +	if (s->extralist.is_empty)
> +		return NULL;
>   	raw_spin_lock(&s->extralist.lock);
>   	node = s->extralist.first;
> -	if (node)
> +	if (node) {
>   		s->extralist.first = node->next;
> +		if (!s->extralist.first)
> +			s->extralist.is_empty = true;
> +	}
>   	raw_spin_unlock(&s->extralist.lock);
>   	return node;
>   }
> @@ -164,15 +178,20 @@ ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
>   	orig_cpu = cpu = raw_smp_processor_id();
>   	while (1) {
>   		head = per_cpu_ptr(s->freelist, cpu);
> +		if (head->is_empty)

This should use READ_ONCE/WRITE_ONCE pair for head->is_empty.

> +			goto next_cpu;
>   		if (raw_spin_trylock(&head->lock)) {
>   			node = head->first;
>   			if (node) {
>   				head->first = node->next;
> +				if (!head->first)
> +					head->is_empty = true;
>   				raw_spin_unlock(&head->lock);
>   				return node;
>   			}
>   			raw_spin_unlock(&head->lock);
>   		}
> +next_cpu:
>   		cpu = cpumask_next(cpu, cpu_possible_mask);
>   		if (cpu >= nr_cpu_ids)
>   			cpu = 0;
Feng Zhou May 31, 2022, 3:24 a.m. UTC | #2 
在 2022/5/31 上午5:20, Daniel Borkmann 写道:
> On 5/30/22 11:13 AM, Feng zhou wrote:
>> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>>
>> This patch add is_empty in pcpu_freelist_head to check freelist
>> having free or not. If having, grab spin_lock, or check next cpu's
>> freelist.
>>
>> Before patch: hash_map performance
>> ./map_perf_test 1
>> 0:hash_map_perf pre-alloc 975345 events per sec
>> 4:hash_map_perf pre-alloc 855367 events per sec
>> 12:hash_map_perf pre-alloc 860862 events per sec
>> 8:hash_map_perf pre-alloc 849561 events per sec
>> 3:hash_map_perf pre-alloc 849074 events per sec
>> 6:hash_map_perf pre-alloc 847120 events per sec
>> 10:hash_map_perf pre-alloc 845047 events per sec
>> 5:hash_map_perf pre-alloc 841266 events per sec
>> 14:hash_map_perf pre-alloc 849740 events per sec
>> 2:hash_map_perf pre-alloc 839598 events per sec
>> 9:hash_map_perf pre-alloc 838695 events per sec
>> 11:hash_map_perf pre-alloc 845390 events per sec
>> 7:hash_map_perf pre-alloc 834865 events per sec
>> 13:hash_map_perf pre-alloc 842619 events per sec
>> 1:hash_map_perf pre-alloc 804231 events per sec
>> 15:hash_map_perf pre-alloc 795314 events per sec
>>
>> hash_map the worst: no free
>> ./map_perf_test 2048
>> 6:worse hash_map_perf pre-alloc 28628 events per sec
>> 5:worse hash_map_perf pre-alloc 28553 events per sec
>> 11:worse hash_map_perf pre-alloc 28543 events per sec
>> 3:worse hash_map_perf pre-alloc 28444 events per sec
>> 1:worse hash_map_perf pre-alloc 28418 events per sec
>> 7:worse hash_map_perf pre-alloc 28427 events per sec
>> 13:worse hash_map_perf pre-alloc 28330 events per sec
>> 14:worse hash_map_perf pre-alloc 28263 events per sec
>> 9:worse hash_map_perf pre-alloc 28211 events per sec
>> 15:worse hash_map_perf pre-alloc 28193 events per sec
>> 12:worse hash_map_perf pre-alloc 28190 events per sec
>> 10:worse hash_map_perf pre-alloc 28129 events per sec
>> 8:worse hash_map_perf pre-alloc 28116 events per sec
>> 4:worse hash_map_perf pre-alloc 27906 events per sec
>> 2:worse hash_map_perf pre-alloc 27801 events per sec
>> 0:worse hash_map_perf pre-alloc 27416 events per sec
>> 3:worse hash_map_perf pre-alloc 28188 events per sec
>>
>> ftrace trace
>>
>> 0)               |  htab_map_update_elem() {
>> 0)   0.198 us    |    migrate_disable();
>> 0)               |    _raw_spin_lock_irqsave() {
>> 0)   0.157 us    |      preempt_count_add();
>> 0)   0.538 us    |    }
>> 0)   0.260 us    |    lookup_elem_raw();
>> 0)               |    alloc_htab_elem() {
>> 0)               |      __pcpu_freelist_pop() {
>> 0)               |        _raw_spin_lock() {
>> 0)   0.152 us    |          preempt_count_add();
>> 0)   0.352 us    |          native_queued_spin_lock_slowpath();
>> 0)   1.065 us    |        }
>>          |      ...
>> 0)               |        _raw_spin_unlock() {
>> 0)   0.254 us    |          preempt_count_sub();
>> 0)   0.555 us    |        }
>> 0) + 25.188 us   |      }
>> 0) + 25.486 us   |    }
>> 0)               |    _raw_spin_unlock_irqrestore() {
>> 0)   0.155 us    |      preempt_count_sub();
>> 0)   0.454 us    |    }
>> 0)   0.148 us    |    migrate_enable();
>> 0) + 28.439 us   |  }
>>
>> The test machine is 16C, trying to get spin_lock 17 times, in addition
>> to 16c, there is an extralist.
>>
>> after patch: hash_map performance
>> ./map_perf_test 1
>> 0:hash_map_perf pre-alloc 969348 events per sec
>> 10:hash_map_perf pre-alloc 906526 events per sec
>> 11:hash_map_perf pre-alloc 904557 events per sec
>> 9:hash_map_perf pre-alloc 902384 events per sec
>> 15:hash_map_perf pre-alloc 912287 events per sec
>> 14:hash_map_perf pre-alloc 905689 events per sec
>> 12:hash_map_perf pre-alloc 903680 events per sec
>> 13:hash_map_perf pre-alloc 902631 events per sec
>> 8:hash_map_perf pre-alloc 875369 events per sec
>> 4:hash_map_perf pre-alloc 862808 events per sec
>> 1:hash_map_perf pre-alloc 857218 events per sec
>> 2:hash_map_perf pre-alloc 852875 events per sec
>> 5:hash_map_perf pre-alloc 846497 events per sec
>> 6:hash_map_perf pre-alloc 828467 events per sec
>> 3:hash_map_perf pre-alloc 812542 events per sec
>> 7:hash_map_perf pre-alloc 805336 events per sec
>>
>> hash_map worst: no free
>> ./map_perf_test 2048
>> 7:worse hash_map_perf pre-alloc 391104 events per sec
>> 4:worse hash_map_perf pre-alloc 388073 events per sec
>> 5:worse hash_map_perf pre-alloc 387038 events per sec
>> 1:worse hash_map_perf pre-alloc 386546 events per sec
>> 0:worse hash_map_perf pre-alloc 384590 events per sec
>> 11:worse hash_map_perf pre-alloc 379378 events per sec
>> 10:worse hash_map_perf pre-alloc 375480 events per sec
>> 12:worse hash_map_perf pre-alloc 372394 events per sec
>> 6:worse hash_map_perf pre-alloc 367692 events per sec
>> 3:worse hash_map_perf pre-alloc 363970 events per sec
>> 9:worse hash_map_perf pre-alloc 364008 events per sec
>> 8:worse hash_map_perf pre-alloc 363759 events per sec
>> 2:worse hash_map_perf pre-alloc 360743 events per sec
>> 14:worse hash_map_perf pre-alloc 361195 events per sec
>> 13:worse hash_map_perf pre-alloc 360276 events per sec
>> 15:worse hash_map_perf pre-alloc 360057 events per sec
>> 0:worse hash_map_perf pre-alloc 378177 events per sec
>>
>> ftrace trace
>> 0)               |  htab_map_update_elem() {
>> 0)   0.317 us    |    migrate_disable();
>> 0)               |    _raw_spin_lock_irqsave() {
>> 0)   0.260 us    |      preempt_count_add();
>> 0)   1.803 us    |    }
>> 0)   0.276 us    |    lookup_elem_raw();
>> 0)               |    alloc_htab_elem() {
>> 0)   0.586 us    |      __pcpu_freelist_pop();
>> 0)   0.945 us    |    }
>> 0)               |    _raw_spin_unlock_irqrestore() {
>> 0)   0.160 us    |      preempt_count_sub();
>> 0)   0.972 us    |    }
>> 0)   0.657 us    |    migrate_enable();
>> 0)   8.669 us    |  }
>>
>> It can be seen that after adding this patch, the map performance is
>> almost not degraded, and when free=0, first check is_empty instead of
>> directly acquiring spin_lock.
>>
>> As for why to add is_empty instead of directly judging head->first, my
>> understanding is this, head->first is frequently modified during 
>> updating
>> map, which will lead to invalid other cpus's cache, and is_empty is 
>> after
>> freelist having no free elems will be changed, the performance will 
>> be better.
>>
>> Co-developed-by: Chengming Zhou <zhouchengming@bytedance.com>
>> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
>> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
>> ---
>>   kernel/bpf/percpu_freelist.c | 28 +++++++++++++++++++++++++---
>>   kernel/bpf/percpu_freelist.h |  1 +
>>   2 files changed, 26 insertions(+), 3 deletions(-)
> [...]
>>       /* per cpu lists are all empty, try extralist */
>> +    if (s->extralist.is_empty)
>> +        return NULL;
>>       raw_spin_lock(&s->extralist.lock);
>>       node = s->extralist.first;
>> -    if (node)
>> +    if (node) {
>>           s->extralist.first = node->next;
>> +        if (!s->extralist.first)
>> +            s->extralist.is_empty = true;
>> +    }
>>       raw_spin_unlock(&s->extralist.lock);
>>       return node;
>>   }
>> @@ -164,15 +178,20 @@ ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
>>       orig_cpu = cpu = raw_smp_processor_id();
>>       while (1) {
>>           head = per_cpu_ptr(s->freelist, cpu);
>> +        if (head->is_empty)
>
> This should use READ_ONCE/WRITE_ONCE pair for head->is_empty.

Yes, will do. Thanks.

>
>> +            goto next_cpu;
>>           if (raw_spin_trylock(&head->lock)) {
>>               node = head->first;
>>               if (node) {
>>                   head->first = node->next;
>> +                if (!head->first)
>> +                    head->is_empty = true;
>>                   raw_spin_unlock(&head->lock);
>>                   return node;
>>               }
>>               raw_spin_unlock(&head->lock);
>>           }
>> +next_cpu:
>>           cpu = cpumask_next(cpu, cpu_possible_mask);
>>           if (cpu >= nr_cpu_ids)
>>               cpu = 0;
diff mbox series

Patch

diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
index 3d897de89061..f83eb63720d4 100644
--- a/kernel/bpf/percpu_freelist.c
+++ b/kernel/bpf/percpu_freelist.c
@@ -16,9 +16,11 @@  int pcpu_freelist_init(struct pcpu_freelist *s)
 
 		raw_spin_lock_init(&head->lock);
 		head->first = NULL;
+		head->is_empty = true;
 	}
 	raw_spin_lock_init(&s->extralist.lock);
 	s->extralist.first = NULL;
+	s->extralist.is_empty = true;
 	return 0;
 }
 
@@ -32,6 +34,8 @@  static inline void pcpu_freelist_push_node(struct pcpu_freelist_head *head,
 {
 	node->next = head->first;
 	head->first = node;
+	if (head->is_empty)
+		head->is_empty = false;
 }
 
 static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head,
@@ -130,14 +134,19 @@  static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
 	orig_cpu = cpu = raw_smp_processor_id();
 	while (1) {
 		head = per_cpu_ptr(s->freelist, cpu);
+		if (head->is_empty)
+			goto next_cpu;
 		raw_spin_lock(&head->lock);
 		node = head->first;
 		if (node) {
 			head->first = node->next;
+			if (!head->first)
+				head->is_empty = true;
 			raw_spin_unlock(&head->lock);
 			return node;
 		}
 		raw_spin_unlock(&head->lock);
+next_cpu:
 		cpu = cpumask_next(cpu, cpu_possible_mask);
 		if (cpu >= nr_cpu_ids)
 			cpu = 0;
@@ -146,10 +155,15 @@  static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
 	}
 
 	/* per cpu lists are all empty, try extralist */
+	if (s->extralist.is_empty)
+		return NULL;
 	raw_spin_lock(&s->extralist.lock);
 	node = s->extralist.first;
-	if (node)
+	if (node) {
 		s->extralist.first = node->next;
+		if (!s->extralist.first)
+			s->extralist.is_empty = true;
+	}
 	raw_spin_unlock(&s->extralist.lock);
 	return node;
 }
@@ -164,15 +178,20 @@  ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
 	orig_cpu = cpu = raw_smp_processor_id();
 	while (1) {
 		head = per_cpu_ptr(s->freelist, cpu);
+		if (head->is_empty)
+			goto next_cpu;
 		if (raw_spin_trylock(&head->lock)) {
 			node = head->first;
 			if (node) {
 				head->first = node->next;
+				if (!head->first)
+					head->is_empty = true;
 				raw_spin_unlock(&head->lock);
 				return node;
 			}
 			raw_spin_unlock(&head->lock);
 		}
+next_cpu:
 		cpu = cpumask_next(cpu, cpu_possible_mask);
 		if (cpu >= nr_cpu_ids)
 			cpu = 0;
@@ -181,11 +200,14 @@  ___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
 	}
 
 	/* cannot pop from per cpu lists, try extralist */
-	if (!raw_spin_trylock(&s->extralist.lock))
+	if (s->extralist.is_empty || !raw_spin_trylock(&s->extralist.lock))
 		return NULL;
 	node = s->extralist.first;
-	if (node)
+	if (node) {
 		s->extralist.first = node->next;
+		if (!s->extralist.first)
+			s->extralist.is_empty = true;
+	}
 	raw_spin_unlock(&s->extralist.lock);
 	return node;
 }
diff --git a/kernel/bpf/percpu_freelist.h b/kernel/bpf/percpu_freelist.h
index 3c76553cfe57..9e4545631ed5 100644
--- a/kernel/bpf/percpu_freelist.h
+++ b/kernel/bpf/percpu_freelist.h
@@ -9,6 +9,7 @@ 
 struct pcpu_freelist_head {
 	struct pcpu_freelist_node *first;
 	raw_spinlock_t lock;
+	bool is_empty;
 };
 
 struct pcpu_freelist {