Flamegraph handles multi-thread program abnormality

[yuand2022]

The command pipeline is as follows:
perf record -g ./app
perf script > app.perf
cat app.perf | ./stackcollapse-perf.pl --all | ./flamegraph.pl > app.svg

My application is a multi-threaded application and the execution time is about 20 minutes. When I finished executing the above pipeline, I got an unexpected svg image, the flame graph does not truly reflect the actual situation。

ReadAlignChunk::mapChunk is a thread execution function, which should be a hotspot, and BarcodeMap::BarcodeMapping is a sub-function of a thread thread function, which should be a secondary hotspot. Another problem is that the call stack is too shallow, with less than 10 layers, far below expectations.

[HarrySidhuz0008]

import threading
import time
import pyflamegraph

Function to calculate factorial

def calculate_factorial(n):
if n == 0:
return 1
else:
return n * calculate_factorial(n - 1)

Function that simulates multi-threading

def worker(thread_id):
for i in range(1, 5000):
calculate_factorial(20)

def main():
# Start profiling
with pyflamegraph.FlamegraphProfiler(output_file='flamegraph.svg'):
threads = []
for i in range(4): # Create 4 threads
thread = threading.Thread(target=worker, args=(i,))
thread.start()
threads.append(thread)

    for thread in threads:
        thread.join()

if name == 'main':
main()