Application running on both cpus under Linux

Question

Hi there,
I'm using Zynq + PetaLinux that is supposed to use both cpus by default, and I can see that calling the top command. However, when I launch an APP it's just run in one CPU.
We have an APP with 2 threads:
(1) Reads from BRAM in PL (using mmap) and store bytes in main memory.
(2) If there's new data read from bram, send it to PC using Ethernet.
In order to execute each thread in different CPUs, I use the following snippet in each thread (where core_id=0 for thread1 and core_id=1 for thread2):
        int core_id = 0;
        cpu_set_t cpuset;
        CPU_ZERO(&cpuset);
        CPU_SET(core_id, &cpuset);
        pthread_t current_thread = pthread_self();
        pthread_setaffinity_np(current_thread, sizeof(cpu_set_t), &cpuset);
The performance does, in fact, get better with this code, but shouldn't I be able to find both cpus being used calling top command or somewhere else? Because it just shows that cpu0 is being used.
Thank you,
Leroy.

Answer 1

Hi Leroy,
Interesting, you've actually got a slightly newer version of busybox that I am using. Looking at the more recent source code, it appears that threads option has been made configurable. Evidently your version was compiled without this feature.
I was going to suggest trying "ps -T" instead, but it looks like that command also has configurable thread reporting now... and most likely that will be switched off too.
I would suggest compiling your own busybox (even if you only use it for "top"). Or you could also compile the real "top" command from the procps (or procps-ng) package.
If you want something quick, you can look directly in /proc filesystem. Specifically, you can do "cat /proc/PID/status" where PID is the process ID of your task. The "status" file contains a field called "Threads" that tells you how many threads there are. If you want more details on each of the threads, use "ls /proc/PID/task" to get a list of the process ID of each of the threads. Then for each thread, you can consult it's /proc/PID/... fields (for details see http://linux.die.net/man/5/proc).
Regards,
-R