When the BPF ring buffer is full, a new event cannot be recorded until one or more old events are consumed to make enough space for it. In cases such as fault diagnostics, where recent events are more useful than older ones, this mechanism may lead to critical events being lost.
So add overwrite mode for BPF ring buffer to address it. In this mode, the new event overwrites the oldest event when the buffer is full.
v3: - remove half-round wakeup, drop unnecessary min in ringbuf_avail_data_sz(), switch to smp_load_acquire, update tests and fix typos, etc (Andrii) - rebase and re-collect performance data
v2: https://lore.kernel.org/bpf/20250905150641.2078838-1-xukuohai@huaweicloud.co... - remove libbpf changes (Andrii) - update overwrite benchmark
v1: https://lore.kernel.org/bpf/20250804022101.2171981-1-xukuohai@huaweicloud.co...
Xu Kuohai (3): bpf: Add overwrite mode for BPF ring buffer selftests/bpf: Add overwrite mode test for BPF ring buffer selftests/bpf/benchs: Add overwrite mode benchmark for BPF ring buffer
include/uapi/linux/bpf.h | 4 + kernel/bpf/ringbuf.c | 109 +++++++++++++++--- tools/include/uapi/linux/bpf.h | 4 + tools/testing/selftests/bpf/Makefile | 3 +- .../selftests/bpf/benchs/bench_ringbufs.c | 66 ++++++++++- .../bpf/benchs/run_bench_ringbufs.sh | 4 + .../selftests/bpf/prog_tests/ringbuf.c | 64 ++++++++++ .../selftests/bpf/progs/ringbuf_bench.c | 11 ++ .../bpf/progs/test_ringbuf_overwrite.c | 98 ++++++++++++++++ 9 files changed, 337 insertions(+), 26 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c
From: Xu Kuohai xukuohai@huawei.com
When the BPF ring buffer is full, a new event cannot be recorded until one or more old events are consumed to make enough space for it. In cases such as fault diagnostics, where recent events are more useful than older ones, this mechanism may lead to critical events being lost.
So add overwrite mode for BPF ring buffer to address it. In this mode, the new event overwrites the oldest event when the buffer is full.
The basic idea is as follows:
1. producer_pos tracks the next position to record new event. When there is enough free space, producer_pos is simply advanced by producer to make space for the new event.
2. To avoid waiting for consumer when the buffer is full, a new variable, overwrite_pos, is introduced for producer. It points to the oldest event committed in the buffer. It is advanced by producer to discard one or more oldest events to make space for the new event when the buffer is full.
3. pending_pos tracks the oldest event to be committed. pending_pos is never passed by producer_pos, so multiple producers never write to the same position at the same time.
The following example diagrams show how it works in a 4096-byte ring buffer.
1. At first, {producer,overwrite,pending,consumer}_pos are all set to 0.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | +-----------------------------------------------------------------------+ ^ | | producer_pos = 0 overwrite_pos = 0 pending_pos = 0 consumer_pos = 0
2. Now reserve a 512-byte event A.
There is enough free space, so A is allocated at offset 0. And producer_pos is advanced to 512, the end of A. Since A is not submitted, the BUSY bit is set.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | A | | | [BUSY] | | +-----------------------------------------------------------------------+ ^ ^ | | | | | producer_pos = 512 | overwrite_pos = 0 pending_pos = 0 consumer_pos = 0
3. Reserve event B, size 1024.
B is allocated at offset 512 with BUSY bit set, and producer_pos is advanced to the end of B.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | A | B | | | [BUSY] | [BUSY] | | +-----------------------------------------------------------------------+ ^ ^ | | | | | producer_pos = 1536 | overwrite_pos = 0 pending_pos = 0 consumer_pos = 0
4. Reserve event C, size 2048.
C is allocated at offset 1536, and producer_pos is advanced to 3584.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | A | B | C | | | [BUSY] | [BUSY] | [BUSY] | | +-----------------------------------------------------------------------+ ^ ^ | | | | | producer_pos = 3584 | overwrite_pos = 0 pending_pos = 0 consumer_pos = 0
5. Submit event A.
The BUSY bit of A is cleared. B becomes the oldest event to be committed, so pending_pos is advanced to 512, the start of B.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | A | B | C | | | | [BUSY] | [BUSY] | | +-----------------------------------------------------------------------+ ^ ^ ^ | | | | | | | pending_pos = 512 producer_pos = 3584 | overwrite_pos = 0 consumer_pos = 0
6. Submit event B.
The BUSY bit of B is cleared, and pending_pos is advanced to the start of C, which is now the oldest event to be committed.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | A | B | C | | | | | [BUSY] | | +-----------------------------------------------------------------------+ ^ ^ ^ | | | | | | | pending_pos = 1536 producer_pos = 3584 | overwrite_pos = 0 consumer_pos = 0
7. Reserve event D, size 1536 (3 * 512).
There are 2048 bytes not being written between producer_pos (currently 3584) and pending_pos, so D is allocated at offset 3584, and producer_pos is advanced by 1536 (from 3584 to 5120).
Since event D will overwrite all bytes of event A and the first 512 bytes of event B, overwrite_pos is advanced to the start of event C, the oldest event that is not overwritten.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | D End | | C | D Begin| | [BUSY] | | [BUSY] | [BUSY] | +-----------------------------------------------------------------------+ ^ ^ ^ | | | | | pending_pos = 1536 | | overwrite_pos = 1536 | | | producer_pos=5120 | consumer_pos = 0
8. Reserve event E, size 1024.
Although there are 512 bytes not being written between producer_pos and pending_pos, E cannot be reserved, as it would overwrite the first 512 bytes of event C, which is still being written.
9. Submit event C and D.
pending_pos is advanced to the end of D.
0 512 1024 1536 2048 2560 3072 3584 4096 +-----------------------------------------------------------------------+ | | | | | | D End | | C | D Begin| | | | | | +-----------------------------------------------------------------------+ ^ ^ ^ | | | | | overwrite_pos = 1536 | | | producer_pos=5120 | pending_pos=5120 | consumer_pos = 0
The performance data for overwrite mode will be provided in a follow-up patch that adds overwrite-mode benchmarks.
A sample of performance data for non-overwrite mode, collected on an x86_64 CPU and an arm64 CPU, before and after this patch, is shown below. As we can see, no obvious performance regression occurs.
- x86_64 (AMD EPYC 9654)
Before:
Ringbuf, multi-producer contention ================================== rb-libbpf nr_prod 1 11.623 ± 0.027M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 2 15.812 ± 0.014M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 3 7.871 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 4 6.703 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 8 2.896 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 12 2.054 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 16 1.864 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 20 1.580 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 24 1.484 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 28 1.369 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 32 1.316 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 36 1.272 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 40 1.239 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 44 1.226 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 48 1.213 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 52 1.193 ± 0.001M/s (drops 0.000 ± 0.000M/s)
After:
Ringbuf, multi-producer contention ================================== rb-libbpf nr_prod 1 11.845 ± 0.036M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 2 15.889 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 3 8.155 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 4 6.708 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 8 2.918 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 12 2.065 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 16 1.870 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 20 1.582 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 24 1.482 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 28 1.372 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 32 1.323 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 36 1.264 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 40 1.236 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 44 1.209 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 48 1.189 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 52 1.165 ± 0.002M/s (drops 0.000 ± 0.000M/s)
- arm64 (HiSilicon Kunpeng 920)
Before:
Ringbuf, multi-producer contention ================================== rb-libbpf nr_prod 1 11.310 ± 0.623M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 2 9.947 ± 0.004M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 3 6.634 ± 0.011M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 4 4.502 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 8 3.888 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 12 3.372 ± 0.005M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 16 3.189 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 20 2.998 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 24 3.086 ± 0.018M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 28 2.845 ± 0.004M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 32 2.815 ± 0.008M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 36 2.771 ± 0.009M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 40 2.814 ± 0.011M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 44 2.752 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 48 2.695 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 52 2.710 ± 0.006M/s (drops 0.000 ± 0.000M/s)
After:
Ringbuf, multi-producer contention ================================== rb-libbpf nr_prod 1 11.283 ± 0.550M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 2 9.993 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 3 6.898 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 4 5.257 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 8 3.830 ± 0.005M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 12 3.528 ± 0.013M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 16 3.265 ± 0.018M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 20 2.990 ± 0.007M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 24 2.929 ± 0.014M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 28 2.898 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 32 2.818 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 36 2.789 ± 0.012M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 40 2.770 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 44 2.651 ± 0.007M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 48 2.669 ± 0.005M/s (drops 0.000 ± 0.000M/s) rb-libbpf nr_prod 52 2.695 ± 0.009M/s (drops 0.000 ± 0.000M/s)
Signed-off-by: Xu Kuohai xukuohai@huawei.com --- include/uapi/linux/bpf.h | 4 ++ kernel/bpf/ringbuf.c | 109 +++++++++++++++++++++++++++------ tools/include/uapi/linux/bpf.h | 4 ++ 3 files changed, 98 insertions(+), 19 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 6829936d33f5..9fbbbc3dc490 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -1430,6 +1430,9 @@ enum {
/* Do not translate kernel bpf_arena pointers to user pointers */ BPF_F_NO_USER_CONV = (1U << 18), + +/* Enable BPF ringbuf overwrite mode */ + BPF_F_RB_OVERWRITE = (1U << 19), };
/* Flags for BPF_PROG_QUERY. */ @@ -6231,6 +6234,7 @@ enum { BPF_RB_RING_SIZE = 1, BPF_RB_CONS_POS = 2, BPF_RB_PROD_POS = 3, + BPF_RB_OVERWRITE_POS = 4, };
/* BPF ring buffer constants */ diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c index 719d73299397..821929da778e 100644 --- a/kernel/bpf/ringbuf.c +++ b/kernel/bpf/ringbuf.c @@ -13,7 +13,7 @@ #include <linux/btf_ids.h> #include <asm/rqspinlock.h>
-#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE) +#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE | BPF_F_RB_OVERWRITE)
/* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */ #define RINGBUF_PGOFF \ @@ -30,6 +30,7 @@ struct bpf_ringbuf { u64 mask; struct page **pages; int nr_pages; + bool overwrite_mode; rqspinlock_t spinlock ____cacheline_aligned_in_smp; /* For user-space producer ring buffers, an atomic_t busy bit is used * to synchronize access to the ring buffers in the kernel, rather than @@ -72,6 +73,8 @@ struct bpf_ringbuf { */ unsigned long consumer_pos __aligned(PAGE_SIZE); unsigned long producer_pos __aligned(PAGE_SIZE); + /* points to the record right after the last overwritten one */ + unsigned long overwrite_pos; unsigned long pending_pos; char data[] __aligned(PAGE_SIZE); }; @@ -166,7 +169,7 @@ static void bpf_ringbuf_notify(struct irq_work *work) * considering that the maximum value of data_sz is (4GB - 1), there * will be no overflow, so just note the size limit in the comments. */ -static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node) +static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node, bool overwrite_mode) { struct bpf_ringbuf *rb;
@@ -183,17 +186,25 @@ static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node) rb->consumer_pos = 0; rb->producer_pos = 0; rb->pending_pos = 0; + rb->overwrite_mode = overwrite_mode;
return rb; }
static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr) { + bool overwrite_mode = false; struct bpf_ringbuf_map *rb_map;
if (attr->map_flags & ~RINGBUF_CREATE_FLAG_MASK) return ERR_PTR(-EINVAL);
+ if (attr->map_flags & BPF_F_RB_OVERWRITE) { + if (attr->map_type == BPF_MAP_TYPE_USER_RINGBUF) + return ERR_PTR(-EINVAL); + overwrite_mode = true; + } + if (attr->key_size || attr->value_size || !is_power_of_2(attr->max_entries) || !PAGE_ALIGNED(attr->max_entries)) @@ -205,7 +216,7 @@ static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
bpf_map_init_from_attr(&rb_map->map, attr);
- rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node); + rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node, overwrite_mode); if (!rb_map->rb) { bpf_map_area_free(rb_map); return ERR_PTR(-ENOMEM); @@ -293,13 +304,25 @@ static int ringbuf_map_mmap_user(struct bpf_map *map, struct vm_area_struct *vma return remap_vmalloc_range(vma, rb_map->rb, vma->vm_pgoff + RINGBUF_PGOFF); }
+/* Return an estimate of the available data in the ring buffer. + * Note: the returned value can exceed the actual ring buffer size because the + * function is not synchronized with the producer. The producer acquires the + * ring buffer's spinlock, but this function does not. + */ static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb) { - unsigned long cons_pos, prod_pos; + unsigned long cons_pos, prod_pos, over_pos;
cons_pos = smp_load_acquire(&rb->consumer_pos); - prod_pos = smp_load_acquire(&rb->producer_pos); - return prod_pos - cons_pos; + + if (unlikely(rb->overwrite_mode)) { + over_pos = smp_load_acquire(&rb->overwrite_pos); + prod_pos = smp_load_acquire(&rb->producer_pos); + return prod_pos - max(cons_pos, over_pos); + } else { + prod_pos = smp_load_acquire(&rb->producer_pos); + return prod_pos - cons_pos; + } }
static u32 ringbuf_total_data_sz(const struct bpf_ringbuf *rb) @@ -402,11 +425,41 @@ bpf_ringbuf_restore_from_rec(struct bpf_ringbuf_hdr *hdr) return (void*)((addr & PAGE_MASK) - off); }
+static bool bpf_ringbuf_has_space(const struct bpf_ringbuf *rb, + unsigned long new_prod_pos, + unsigned long cons_pos, + unsigned long pend_pos) +{ + /* no space if oldest not yet committed record until the newest + * record span more than (ringbuf_size - 1). + */ + if (new_prod_pos - pend_pos > rb->mask) + return false; + + /* ok, we have space in overwrite mode */ + if (unlikely(rb->overwrite_mode)) + return true; + + /* no space if producer position advances more than (ringbuf_size - 1) + * ahead of consumer position when not in overwrite mode. + */ + if (new_prod_pos - cons_pos > rb->mask) + return false; + + return true; +} + +static u32 bpf_ringbuf_round_up_hdr_len(u32 hdr_len) +{ + hdr_len &= ~BPF_RINGBUF_DISCARD_BIT; + return round_up(hdr_len + BPF_RINGBUF_HDR_SZ, 8); +} + static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) { - unsigned long cons_pos, prod_pos, new_prod_pos, pend_pos, flags; + unsigned long cons_pos, prod_pos, new_prod_pos, pend_pos, over_pos, flags; struct bpf_ringbuf_hdr *hdr; - u32 len, pg_off, tmp_size, hdr_len; + u32 len, pg_off, hdr_len;
if (unlikely(size > RINGBUF_MAX_RECORD_SZ)) return NULL; @@ -429,24 +482,40 @@ static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size) hdr_len = READ_ONCE(hdr->len); if (hdr_len & BPF_RINGBUF_BUSY_BIT) break; - tmp_size = hdr_len & ~BPF_RINGBUF_DISCARD_BIT; - tmp_size = round_up(tmp_size + BPF_RINGBUF_HDR_SZ, 8); - pend_pos += tmp_size; + pend_pos += bpf_ringbuf_round_up_hdr_len(hdr_len); } rb->pending_pos = pend_pos;
- /* check for out of ringbuf space: - * - by ensuring producer position doesn't advance more than - * (ringbuf_size - 1) ahead - * - by ensuring oldest not yet committed record until newest - * record does not span more than (ringbuf_size - 1) - */ - if (new_prod_pos - cons_pos > rb->mask || - new_prod_pos - pend_pos > rb->mask) { + if (!bpf_ringbuf_has_space(rb, new_prod_pos, cons_pos, pend_pos)) { raw_res_spin_unlock_irqrestore(&rb->spinlock, flags); return NULL; }
+ /* In overwrite mode, advance overwrite_pos when the ring buffer is full. + * The key points are to stay on record boundaries and consume enough records + * to fit the new one. + */ + if (unlikely(rb->overwrite_mode)) { + over_pos = rb->overwrite_pos; + while (new_prod_pos - over_pos > rb->mask) { + hdr = (void *)rb->data + (over_pos & rb->mask); + hdr_len = READ_ONCE(hdr->len); + /* The bpf_ringbuf_has_space() check above ensures we won’t + * step over a record currently being worked on by another + * producer. + */ + over_pos += bpf_ringbuf_round_up_hdr_len(hdr_len); + } + /* smp_store_release(&rb->producer_pos, new_prod_pos) at + * the end of the function ensures that when consumer sees + * the updated rb->producer_pos, it always sees the updated + * rb->overwrite_pos, so when consumer reads overwrite_pos + * after smp_load_acquire(r->producer_pos), the overwrite_pos + * will always be valid. + */ + WRITE_ONCE(rb->overwrite_pos, over_pos); + } + hdr = (void *)rb->data + (prod_pos & rb->mask); pg_off = bpf_ringbuf_rec_pg_off(rb, hdr); hdr->len = size | BPF_RINGBUF_BUSY_BIT; @@ -576,6 +645,8 @@ BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags) return smp_load_acquire(&rb->consumer_pos); case BPF_RB_PROD_POS: return smp_load_acquire(&rb->producer_pos); + case BPF_RB_OVERWRITE_POS: + return smp_load_acquire(&rb->overwrite_pos); default: return 0; } diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 6829936d33f5..9fbbbc3dc490 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -1430,6 +1430,9 @@ enum {
/* Do not translate kernel bpf_arena pointers to user pointers */ BPF_F_NO_USER_CONV = (1U << 18), + +/* Enable BPF ringbuf overwrite mode */ + BPF_F_RB_OVERWRITE = (1U << 19), };
/* Flags for BPF_PROG_QUERY. */ @@ -6231,6 +6234,7 @@ enum { BPF_RB_RING_SIZE = 1, BPF_RB_CONS_POS = 2, BPF_RB_PROD_POS = 3, + BPF_RB_OVERWRITE_POS = 4, };
/* BPF ring buffer constants */
From: Xu Kuohai xukuohai@huawei.com
Add overwrite mode test for BPF ring buffer. The test creates a BPF ring buffer in overwrite mode, then repeatedly reserves and commits records to check if the ring buffer works as expected both before and after overwriting occurs.
Signed-off-by: Xu Kuohai xukuohai@huawei.com --- tools/testing/selftests/bpf/Makefile | 3 +- .../selftests/bpf/prog_tests/ringbuf.c | 64 ++++++++++++ .../bpf/progs/test_ringbuf_overwrite.c | 98 +++++++++++++++++++ 3 files changed, 164 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index f00587d4ede6..43d133bf514d 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -498,7 +498,8 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h \
LSKELS := fexit_sleep.c trace_printk.c trace_vprintk.c map_ptr_kern.c \ core_kern.c core_kern_overflow.c test_ringbuf.c \ - test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c + test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c \ + test_ringbuf_overwrite.c
LSKELS_SIGNED := fentry_test.c fexit_test.c atomics.c
diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c index d1e4cb28a72c..5264af1dc768 100644 --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c @@ -17,6 +17,7 @@ #include "test_ringbuf_n.lskel.h" #include "test_ringbuf_map_key.lskel.h" #include "test_ringbuf_write.lskel.h" +#include "test_ringbuf_overwrite.lskel.h"
#define EDONE 7777
@@ -497,6 +498,67 @@ static void ringbuf_map_key_subtest(void) test_ringbuf_map_key_lskel__destroy(skel_map_key); }
+static void ringbuf_overwrite_mode_subtest(void) +{ + unsigned long size, len1, len2, len3, len4, len5; + unsigned long expect_avail_data, expect_prod_pos, expect_over_pos; + struct test_ringbuf_overwrite_lskel *skel; + int err; + + skel = test_ringbuf_overwrite_lskel__open(); + if (!ASSERT_OK_PTR(skel, "skel_open")) + return; + + size = 0x1000; + len1 = 0x800; + len2 = 0x400; + len3 = size - len1 - len2 - BPF_RINGBUF_HDR_SZ * 3; /* 0x3e8 */ + len4 = len3 - 8; /* 0x3e0 */ + len5 = len3; /* retry with len3 */ + + skel->maps.ringbuf.max_entries = size; + skel->rodata->LEN1 = len1; + skel->rodata->LEN2 = len2; + skel->rodata->LEN3 = len3; + skel->rodata->LEN4 = len4; + skel->rodata->LEN5 = len5; + + skel->bss->pid = getpid(); + + err = test_ringbuf_overwrite_lskel__load(skel); + if (!ASSERT_OK(err, "skel_load")) + goto cleanup; + + err = test_ringbuf_overwrite_lskel__attach(skel); + if (!ASSERT_OK(err, "skel_attach")) + goto cleanup; + + syscall(__NR_getpgid); + + ASSERT_EQ(skel->bss->reserve1_fail, 0, "reserve 1"); + ASSERT_EQ(skel->bss->reserve2_fail, 0, "reserve 2"); + ASSERT_EQ(skel->bss->reserve3_fail, 1, "reserve 3"); + ASSERT_EQ(skel->bss->reserve4_fail, 0, "reserve 4"); + ASSERT_EQ(skel->bss->reserve5_fail, 0, "reserve 5"); + + ASSERT_EQ(skel->bss->ring_size, size, "check_ring_size"); + + expect_avail_data = len2 + len4 + len5 + 3 * BPF_RINGBUF_HDR_SZ; + ASSERT_EQ(skel->bss->avail_data, expect_avail_data, "check_avail_size"); + + ASSERT_EQ(skel->bss->cons_pos, 0, "check_cons_pos"); + + expect_prod_pos = len1 + len2 + len4 + len5 + 4 * BPF_RINGBUF_HDR_SZ; + ASSERT_EQ(skel->bss->prod_pos, expect_prod_pos, "check_prod_pos"); + + expect_over_pos = len1 + BPF_RINGBUF_HDR_SZ; + ASSERT_EQ(skel->bss->over_pos, expect_over_pos, "check_over_pos"); + + test_ringbuf_overwrite_lskel__detach(skel); +cleanup: + test_ringbuf_overwrite_lskel__destroy(skel); +} + void test_ringbuf(void) { if (test__start_subtest("ringbuf")) @@ -507,4 +569,6 @@ void test_ringbuf(void) ringbuf_map_key_subtest(); if (test__start_subtest("ringbuf_write")) ringbuf_write_subtest(); + if (test__start_subtest("ringbuf_overwrite_mode")) + ringbuf_overwrite_mode_subtest(); } diff --git a/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c b/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c new file mode 100644 index 000000000000..ff4aa67ddacc --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c @@ -0,0 +1,98 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (C) 2025. Huawei Technologies Co., Ltd */ + +#include <linux/bpf.h> +#include <bpf/bpf_helpers.h> +#include "bpf_misc.h" + +char _license[] SEC("license") = "GPL"; + +struct { + __uint(type, BPF_MAP_TYPE_RINGBUF); + __uint(map_flags, BPF_F_RB_OVERWRITE); +} ringbuf SEC(".maps"); + +int pid; + +const volatile unsigned long LEN1; +const volatile unsigned long LEN2; +const volatile unsigned long LEN3; +const volatile unsigned long LEN4; +const volatile unsigned long LEN5; + +long reserve1_fail = 0; +long reserve2_fail = 0; +long reserve3_fail = 0; +long reserve4_fail = 0; +long reserve5_fail = 0; + +unsigned long avail_data = 0; +unsigned long ring_size = 0; +unsigned long cons_pos = 0; +unsigned long prod_pos = 0; +unsigned long over_pos = 0; + +SEC("fentry/" SYS_PREFIX "sys_getpgid") +int test_overwrite_ringbuf(void *ctx) +{ + char *rec1, *rec2, *rec3, *rec4, *rec5; + int cur_pid = bpf_get_current_pid_tgid() >> 32; + + if (cur_pid != pid) + return 0; + + rec1 = bpf_ringbuf_reserve(&ringbuf, LEN1, 0); + if (!rec1) { + reserve1_fail = 1; + return 0; + } + + rec2 = bpf_ringbuf_reserve(&ringbuf, LEN2, 0); + if (!rec2) { + bpf_ringbuf_discard(rec1, 0); + reserve2_fail = 1; + return 0; + } + + rec3 = bpf_ringbuf_reserve(&ringbuf, LEN3, 0); + /* expect failure */ + if (!rec3) { + reserve3_fail = 1; + } else { + bpf_ringbuf_discard(rec1, 0); + bpf_ringbuf_discard(rec2, 0); + bpf_ringbuf_discard(rec3, 0); + return 0; + } + + rec4 = bpf_ringbuf_reserve(&ringbuf, LEN4, 0); + if (!rec4) { + reserve4_fail = 1; + bpf_ringbuf_discard(rec1, 0); + bpf_ringbuf_discard(rec2, 0); + return 0; + } + + bpf_ringbuf_submit(rec1, 0); + bpf_ringbuf_submit(rec2, 0); + bpf_ringbuf_submit(rec4, 0); + + rec5 = bpf_ringbuf_reserve(&ringbuf, LEN5, 0); + if (!rec5) { + reserve5_fail = 1; + return 0; + } + + for (int i = 0; i < LEN3; i++) + rec5[i] = 0xdd; + + bpf_ringbuf_submit(rec5, 0); + + ring_size = bpf_ringbuf_query(&ringbuf, BPF_RB_RING_SIZE); + avail_data = bpf_ringbuf_query(&ringbuf, BPF_RB_AVAIL_DATA); + cons_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_CONS_POS); + prod_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_PROD_POS); + over_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_OVERWRITE_POS); + + return 0; +}
From: Xu Kuohai xukuohai@huawei.com
Add --rb-overwrite option to benchmark BPF ring buffer in overwrite mode. Since overwrite mode is not yet supported by libbpf for consumer, also add --rb-bench-producer option to benchmark producer directly without a consumer.
Benchmarks on an x86_64 and an arm64 CPU are shown below for reference.
- AMD EPYC 9654 (x86_64)
Ringbuf, multi-producer contention in overwrite mode, no consumer ================================================================= rb-prod nr_prod 1 32.180 ± 0.033M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 2 9.617 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 3 8.810 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 4 9.272 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 8 9.173 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 12 3.086 ± 0.032M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 16 2.945 ± 0.021M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 20 2.519 ± 0.021M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 24 2.545 ± 0.021M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 28 2.363 ± 0.024M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 32 2.357 ± 0.021M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 36 2.267 ± 0.011M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 40 2.284 ± 0.020M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 44 2.215 ± 0.025M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 48 2.193 ± 0.023M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 52 2.208 ± 0.024M/s (drops 0.000 ± 0.000M/s)
- HiSilicon Kunpeng 920 (arm64)
Ringbuf, multi-producer contention in overwrite mode, no consumer ================================================================= rb-prod nr_prod 1 14.478 ± 0.006M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 2 21.787 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 3 6.045 ± 0.001M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 4 5.352 ± 0.003M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 8 4.850 ± 0.002M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 12 3.542 ± 0.016M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 16 3.509 ± 0.021M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 20 3.171 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 24 3.154 ± 0.014M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 28 2.974 ± 0.015M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 32 3.167 ± 0.014M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 36 2.903 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 40 2.866 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 44 2.914 ± 0.010M/s (drops 0.000 ± 0.000M/s) rb-prod nr_prod 48 2.806 ± 0.012M/s (drops 0.000 ± 0.000M/s) Rb-prod nr_prod 52 2.840 ± 0.012M/s (drops 0.000 ± 0.000M/s)
Signed-off-by: Xu Kuohai xukuohai@huawei.com --- .../selftests/bpf/benchs/bench_ringbufs.c | 66 +++++++++++++++++-- .../bpf/benchs/run_bench_ringbufs.sh | 4 ++ .../selftests/bpf/progs/ringbuf_bench.c | 11 ++++ 3 files changed, 75 insertions(+), 6 deletions(-)
diff --git a/tools/testing/selftests/bpf/benchs/bench_ringbufs.c b/tools/testing/selftests/bpf/benchs/bench_ringbufs.c index e1ee979e6acc..212859fb2961 100644 --- a/tools/testing/selftests/bpf/benchs/bench_ringbufs.c +++ b/tools/testing/selftests/bpf/benchs/bench_ringbufs.c @@ -19,6 +19,8 @@ static struct { int ringbuf_sz; /* per-ringbuf, in bytes */ bool ringbuf_use_output; /* use slower output API */ int perfbuf_sz; /* per-CPU size, in pages */ + bool overwrite; + bool bench_producer; } args = { .back2back = false, .batch_cnt = 500, @@ -27,6 +29,8 @@ static struct { .ringbuf_sz = 512 * 1024, .ringbuf_use_output = false, .perfbuf_sz = 128, + .overwrite = false, + .bench_producer = false, };
enum { @@ -35,6 +39,8 @@ enum { ARG_RB_BATCH_CNT = 2002, ARG_RB_SAMPLED = 2003, ARG_RB_SAMPLE_RATE = 2004, + ARG_RB_OVERWRITE = 2005, + ARG_RB_BENCH_PRODUCER = 2006, };
static const struct argp_option opts[] = { @@ -43,6 +49,8 @@ static const struct argp_option opts[] = { { "rb-batch-cnt", ARG_RB_BATCH_CNT, "CNT", 0, "Set BPF-side record batch count"}, { "rb-sampled", ARG_RB_SAMPLED, NULL, 0, "Notification sampling"}, { "rb-sample-rate", ARG_RB_SAMPLE_RATE, "RATE", 0, "Notification sample rate"}, + { "rb-overwrite", ARG_RB_OVERWRITE, NULL, 0, "Overwrite mode"}, + { "rb-bench-producer", ARG_RB_BENCH_PRODUCER, NULL, 0, "Benchmark producer"}, {}, };
@@ -72,6 +80,12 @@ static error_t parse_arg(int key, char *arg, struct argp_state *state) argp_usage(state); } break; + case ARG_RB_OVERWRITE: + args.overwrite = true; + break; + case ARG_RB_BENCH_PRODUCER: + args.bench_producer = true; + break; default: return ARGP_ERR_UNKNOWN; } @@ -95,8 +109,33 @@ static inline void bufs_trigger_batch(void)
static void bufs_validate(void) { - if (env.consumer_cnt != 1) { - fprintf(stderr, "rb-libbpf benchmark needs one consumer!\n"); + if (args.bench_producer && strcmp(env.bench_name, "rb-libbpf")) { + fprintf(stderr, "--rb-bench-producer only works with rb-libbpf!\n"); + exit(1); + } + + if (args.overwrite && !args.bench_producer) { + fprintf(stderr, "overwrite mode only works with --rb-bench-producer for now!\n"); + exit(1); + } + + if (args.bench_producer && env.consumer_cnt != 0) { + fprintf(stderr, "no consumer is needed for --rb-bench-producer!\n"); + exit(1); + } + + if (args.bench_producer && args.back2back) { + fprintf(stderr, "back-to-back mode makes no sense for --rb-bench-producer!\n"); + exit(1); + } + + if (args.bench_producer && args.sampled) { + fprintf(stderr, "sampling mode makes no sense for --rb-bench-producer!\n"); + exit(1); + } + + if (!args.bench_producer && env.consumer_cnt != 1) { + fprintf(stderr, "benchmarks without --rb-bench-producer require exactly one consumer!\n"); exit(1); }
@@ -128,12 +167,17 @@ static void ringbuf_libbpf_measure(struct bench_res *res) { struct ringbuf_libbpf_ctx *ctx = &ringbuf_libbpf_ctx;
- res->hits = atomic_swap(&buf_hits.value, 0); + if (args.bench_producer) + res->hits = atomic_swap(&ctx->skel->bss->hits, 0); + else + res->hits = atomic_swap(&buf_hits.value, 0); res->drops = atomic_swap(&ctx->skel->bss->dropped, 0); }
static struct ringbuf_bench *ringbuf_setup_skeleton(void) { + __u32 flags; + struct bpf_map *ringbuf; struct ringbuf_bench *skel;
setup_libbpf(); @@ -146,12 +190,19 @@ static struct ringbuf_bench *ringbuf_setup_skeleton(void)
skel->rodata->batch_cnt = args.batch_cnt; skel->rodata->use_output = args.ringbuf_use_output ? 1 : 0; + skel->rodata->bench_producer = args.bench_producer;
if (args.sampled) /* record data + header take 16 bytes */ skel->rodata->wakeup_data_size = args.sample_rate * 16;
- bpf_map__set_max_entries(skel->maps.ringbuf, args.ringbuf_sz); + ringbuf = skel->maps.ringbuf; + if (args.overwrite) { + flags = bpf_map__map_flags(ringbuf) | BPF_F_RB_OVERWRITE; + bpf_map__set_map_flags(ringbuf, flags); + } + + bpf_map__set_max_entries(ringbuf, args.ringbuf_sz);
if (ringbuf_bench__load(skel)) { fprintf(stderr, "failed to load skeleton\n"); @@ -171,10 +222,13 @@ static void ringbuf_libbpf_setup(void) { struct ringbuf_libbpf_ctx *ctx = &ringbuf_libbpf_ctx; struct bpf_link *link; + int map_fd;
ctx->skel = ringbuf_setup_skeleton(); - ctx->ringbuf = ring_buffer__new(bpf_map__fd(ctx->skel->maps.ringbuf), - buf_process_sample, NULL, NULL); + + map_fd = bpf_map__fd(ctx->skel->maps.ringbuf); + ctx->ringbuf = ring_buffer__new(map_fd, buf_process_sample, + NULL, NULL); if (!ctx->ringbuf) { fprintf(stderr, "failed to create ringbuf\n"); exit(1); diff --git a/tools/testing/selftests/bpf/benchs/run_bench_ringbufs.sh b/tools/testing/selftests/bpf/benchs/run_bench_ringbufs.sh index 91e3567962ff..83e05e837871 100755 --- a/tools/testing/selftests/bpf/benchs/run_bench_ringbufs.sh +++ b/tools/testing/selftests/bpf/benchs/run_bench_ringbufs.sh @@ -49,3 +49,7 @@ for b in 1 2 3 4 8 12 16 20 24 28 32 36 40 44 48 52; do summarize "rb-libbpf nr_prod $b" "$($RUN_RB_BENCH -p$b --rb-batch-cnt 50 rb-libbpf)" done
+header "Ringbuf, multi-producer contention in overwrite mode, no consumer" +for b in 1 2 3 4 8 12 16 20 24 28 32 36 40 44 48 52; do + summarize "rb-prod nr_prod $b" "$($RUN_BENCH -p$b --rb-batch-cnt 50 --rb-overwrite --rb-bench-producer rb-libbpf)" +done diff --git a/tools/testing/selftests/bpf/progs/ringbuf_bench.c b/tools/testing/selftests/bpf/progs/ringbuf_bench.c index 6a468496f539..d96c7d1e8fc2 100644 --- a/tools/testing/selftests/bpf/progs/ringbuf_bench.c +++ b/tools/testing/selftests/bpf/progs/ringbuf_bench.c @@ -1,6 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 // Copyright (c) 2020 Facebook
+#include <stdbool.h> #include <linux/bpf.h> #include <stdint.h> #include <bpf/bpf_helpers.h> @@ -14,9 +15,11 @@ struct {
const volatile int batch_cnt = 0; const volatile long use_output = 0; +const volatile bool bench_producer = false;
long sample_val = 42; long dropped __attribute__((aligned(128))) = 0; +long hits __attribute__((aligned(128))) = 0;
const volatile long wakeup_data_size = 0;
@@ -24,6 +27,9 @@ static __always_inline long get_flags() { long sz;
+ if (bench_producer) + return BPF_RB_NO_WAKEUP; + if (!wakeup_data_size) return 0;
@@ -47,6 +53,8 @@ int bench_ringbuf(void *ctx) *sample = sample_val; flags = get_flags(); bpf_ringbuf_submit(sample, flags); + if (bench_producer) + __sync_add_and_fetch(&hits, 1); } } } else { @@ -55,6 +63,9 @@ int bench_ringbuf(void *ctx) if (bpf_ringbuf_output(&ringbuf, &sample_val, sizeof(sample_val), flags)) __sync_add_and_fetch(&dropped, 1); + else if (bench_producer) + __sync_add_and_fetch(&hits, 1); + } } return 0;
linux-kselftest-mirror@lists.linaro.org
-
Xu Kuohai