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authorYonghong Song <yhs@fb.com>2017-10-05 09:19:20 -0700
committerDavid S. Miller <davem@davemloft.net>2017-10-07 23:05:57 +0100
commit908432ca84fc229e906ba164219e9ad0fe56f755 (patch)
tree042a24e92305abbd98d761b695356d5d82760a61 /kernel/trace
parent97562633bcbac4a07d605ae628d7655fa71caaf5 (diff)
bpf: add helper bpf_perf_event_read_value for perf event array map
Hardware pmu counters are limited resources. When there are more pmu based perf events opened than available counters, kernel will multiplex these events so each event gets certain percentage (but not 100%) of the pmu time. In case that multiplexing happens, the number of samples or counter value will not reflect the case compared to no multiplexing. This makes comparison between different runs difficult. Typically, the number of samples or counter value should be normalized before comparing to other experiments. The typical normalization is done like: normalized_num_samples = num_samples * time_enabled / time_running normalized_counter_value = counter_value * time_enabled / time_running where time_enabled is the time enabled for event and time_running is the time running for event since last normalization. This patch adds helper bpf_perf_event_read_value for kprobed based perf event array map, to read perf counter and enabled/running time. The enabled/running time is accumulated since the perf event open. To achieve scaling factor between two bpf invocations, users can can use cpu_id as the key (which is typical for perf array usage model) to remember the previous value and do the calculation inside the bpf program. Signed-off-by: Yonghong Song <yhs@fb.com> Acked-by: Alexei Starovoitov <ast@fb.com> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/bpf_trace.c45
1 files changed, 41 insertions, 4 deletions
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 95888ae6c263..0be86cc0130e 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -255,14 +255,14 @@ const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
return &bpf_trace_printk_proto;
}
-BPF_CALL_2(bpf_perf_event_read, struct bpf_map *, map, u64, flags)
+static __always_inline int
+get_map_perf_counter(struct bpf_map *map, u64 flags,
+ u64 *value, u64 *enabled, u64 *running)
{
struct bpf_array *array = container_of(map, struct bpf_array, map);
unsigned int cpu = smp_processor_id();
u64 index = flags & BPF_F_INDEX_MASK;
struct bpf_event_entry *ee;
- u64 value = 0;
- int err;
if (unlikely(flags & ~(BPF_F_INDEX_MASK)))
return -EINVAL;
@@ -275,7 +275,15 @@ BPF_CALL_2(bpf_perf_event_read, struct bpf_map *, map, u64, flags)
if (!ee)
return -ENOENT;
- err = perf_event_read_local(ee->event, &value, NULL, NULL);
+ return perf_event_read_local(ee->event, value, enabled, running);
+}
+
+BPF_CALL_2(bpf_perf_event_read, struct bpf_map *, map, u64, flags)
+{
+ u64 value = 0;
+ int err;
+
+ err = get_map_perf_counter(map, flags, &value, NULL, NULL);
/*
* this api is ugly since we miss [-22..-2] range of valid
* counter values, but that's uapi
@@ -293,6 +301,33 @@ static const struct bpf_func_proto bpf_perf_event_read_proto = {
.arg2_type = ARG_ANYTHING,
};
+BPF_CALL_4(bpf_perf_event_read_value, struct bpf_map *, map, u64, flags,
+ struct bpf_perf_event_value *, buf, u32, size)
+{
+ int err = -EINVAL;
+
+ if (unlikely(size != sizeof(struct bpf_perf_event_value)))
+ goto clear;
+ err = get_map_perf_counter(map, flags, &buf->counter, &buf->enabled,
+ &buf->running);
+ if (unlikely(err))
+ goto clear;
+ return 0;
+clear:
+ memset(buf, 0, size);
+ return err;
+}
+
+static const struct bpf_func_proto bpf_perf_event_read_value_proto = {
+ .func = bpf_perf_event_read_value,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_CONST_MAP_PTR,
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_PTR_TO_UNINIT_MEM,
+ .arg4_type = ARG_CONST_SIZE,
+};
+
static DEFINE_PER_CPU(struct perf_sample_data, bpf_sd);
static __always_inline u64
@@ -499,6 +534,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
return &bpf_perf_event_output_proto;
case BPF_FUNC_get_stackid:
return &bpf_get_stackid_proto;
+ case BPF_FUNC_perf_event_read_value:
+ return &bpf_perf_event_read_value_proto;
default:
return tracing_func_proto(func_id);
}