kernel has better response time under stress
Hi all,
I have and stange behavior that I fail to understand:
For performance measurement purpose, I'm using the 'old' parrallel port interface to generate IRQs on a debian kernel 3.2.0-4-amd64 (I am using an externel signal generator connected to tha ACK pin).
I wrote my own kernel module (top half only) to handle the interrupt and send an external signal back to the parrallel port and display both signals on a oscilloscope so I can measure the kernel response time.
Everything works as expected and I can see an average 70 µs of time response with some 'burst' of 20µs . I'm running on a "Intel(R) Core(TM) i3-3240 CPU @ 3.40GHz".
Now, the "unexplained" part.
If I load the CPU, memory and I/O using the "stress" program, I expected the average time to be worst , but the opposit happens: my average response time drops to 20µs.
I tried on 3 differents kernel:
vanilla, PREEMT-RT anf vanilla with NO_HZ option set to false.
Can someone explain the magic of this ?
|