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feat: agent - eBPF Add delay threshold check for push period #7607

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merged 1 commit into from
Jul 30, 2024
Merged

feat: agent - eBPF Add delay threshold check for push period #7607

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3 changes: 0 additions & 3 deletions agent/src/ebpf/kernel/include/task_struct_utils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,6 @@
#include <math.h>
#include "utils.h"

#define NSEC_PER_SEC 1000000000L
#define USER_HZ 100

static __inline void *get_socket_file_addr_with_check(struct task_struct *task,
int fd_num,
int files_off,
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20 changes: 19 additions & 1 deletion agent/src/ebpf/kernel/socket_trace.bpf.c
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Expand Up @@ -2372,7 +2372,14 @@ static __inline int output_data_common(void *ctx)
offsetof(typeof(struct __socket_data), data) + v->data_len;
v_buff->events_num++;

if (v_buff->events_num >= EVENT_BURST_NUM ||
/*
* If the delay of the periodic push event exceeds the threshold, it
* will be pushed immediately.
*/
__u64 curr_time = bpf_ktime_get_ns();
__u64 diff = curr_time - tracer_ctx->last_period_timestamp;
if (diff > PERIODIC_PUSH_DELAY_THRESHOLD_NS ||
v_buff->events_num >= EVENT_BURST_NUM ||
((sizeof(v_buff->data) - v_buff->len) < sizeof(*v))) {
__u32 buf_size =
(v_buff->len +
Expand All @@ -2399,6 +2406,17 @@ static __inline int output_data_common(void *ctx)

v_buff->events_num = 0;
v_buff->len = 0;
if (diff > PERIODIC_PUSH_DELAY_THRESHOLD_NS) {
struct trace_stats *stats;
tracer_ctx->last_period_timestamp =
tracer_ctx->period_timestamp;
tracer_ctx->period_timestamp = curr_time;
stats = trace_stats_map__lookup(&k0);
if (stats == NULL)
goto clear_args_map_1;
if (diff > stats->period_event_max_delay)
stats->period_event_max_delay = diff;
}
}

clear_args_map_1:
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18 changes: 18 additions & 0 deletions agent/src/ebpf/user/config.h
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Expand Up @@ -284,4 +284,22 @@ enum {
#define STACKMAP_SCALING_FACTOR 3.0
#define STACKMAP_CAPACITY_THRESHOLD 32768 // The capacity limit of the Stack trace map, power of two.

/*
* eBPF utilizes perf event's periodic events to push all data residing in the kernel
* cache. We have set this to push data from the kernel buffer every 10 milliseconds.
* This periodic event is implemented using the kernel's high-resolution timer (hrtimer),
* which triggers a timer interrupt when the specified time elapses. However, in practice,
* this timer does not always trigger interrupts precisely every 10 milliseconds to execute
* the eBPF program. This discrepancy occurs because timer interrupts may be masked off
* during certain operations, such as when interrupts are disabled during locking operations.
* Therefore, the timer may trigger interrupts after the expected time, resulting in latency
* for periodic events.
*
* The system call phase will check the time delay of the push period, and if it exceeds this
* threshold, the data will be pushed immediately. From the tests, the maximum delay is
* approximately in the range of 30 to 60 milliseconds. Therefore, it is appropriate to set the
* threshold for the system call phase check to 60 milliseconds.
*/
#define PERIODIC_PUSH_DELAY_THRESHOLD_NS 60000000ULL // 60 milliseconds

#endif /* DF_EBPF_CONFIG_H */
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