Simple BCC script to check if hardware accelerated decoding with libva is being used

trace-libva.py

#!/usr/bin/python3
from bcc import BPF

# I just wanted to check if hardware acceleration for video decoding in firefox is
# actually being used. Thus I wrote this simple BCC script to check whether trace_va_render
# inside libva.so is being called.

# BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <linux/sched.h>
#include <linux/string.h>

#define TASK_COMM_LEN 16

BPF_PERF_OUTPUT(events);

struct data_t {
    u64 pid;
    u64 timestamp;
    char comm[TASK_COMM_LEN];
};

int trace_va_render(struct pt_regs *ctx) {
    struct data_t data = {};
    
    data.pid = bpf_get_current_pid_tgid();
    data.timestamp = bpf_ktime_get_ns();
    bpf_get_current_comm(&data.comm, sizeof(data.comm));
    
    events.perf_submit(ctx, &data, sizeof(data));
    return 0;
}
"""

# Initialize BPF
b = BPF(text=bpf_text)

# Attach the probe to vaRenderPicture in libva.so
b.attach_uprobe(name="/var/home/offlinehq/.local/share/flatpak/runtime/org.freedesktop.Platform/x86_64/24.08/fe5c0ca6b765a89629a24cedce80c20b7d15918e5bae4f35c8f698f4f85c8ecf/files/lib/x86_64-linux-gnu/libva.so.2.2200.0", sym="vaRenderPicture", fn_name="trace_va_render")

# Print header
print("%-18s %-16s %-6s %s" % ("TIME(s)", "COMM", "PID", "EVENT"))

# Process events
start = 0
def print_event(cpu, data, size):
    global start
    event = b["events"].event(data)
    if start == 0:
        start = event.timestamp
    time_s = (float(event.timestamp - start)) / 1000000000
    print("%-18.9f %-16s %-6d %s" % (time_s, event.comm.decode(),
        event.pid, "vaRenderPicture"))

b["events"].open_perf_buffer(print_event)
print("Tracing vaRenderPicture calls... Hit Ctrl+C to end.")

# Loop and print events
while 1:
    try:
        b.perf_buffer_poll()
    except KeyboardInterrupt:
        exit()