Public bug reported: Multithreading simply is not working on my computer, as it is not only using only one processor, the threads are not switching. One completes and then another completes, even though the two are independent and take 20 seconds of cpu time each.
The code is here: http://en.wikipedia.org/wiki/Pthreads I compiled with these options: g++ multicore.c -D_POSIX_PTHREAD_SEMANTICS -lpthread -pthread -o multicore ( I saved the code as multicore.c ) And this command: /usr/bin/time -v ./multicore got this response: a a a a a a a a a a a a a a a a a a a a b b b b b b b b b b b b b b b b b b b b Command being timed: "./multicore" User time (seconds): 11.34 System time (seconds): 0.07 Percent of CPU this job got: 70% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:16.30 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 0 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 0 Minor (reclaiming a frame) page faults: 287 Voluntary context switches: 1 Involuntary context switches: 3737 Swaps: 0 File system inputs: 0 File system outputs: 0 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0 The a's and b's should be mixed evenly throughout the stream. They obviously are not. This is en excerpt from top, running while "multicore" is running. Cpu0 :100.0%us, 0.0%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Cpu1 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st As it shows, even though the is cpu-bound multi-threaded work to be done, the second core is not being utilized at all. To prove I have two processors, this command: grep processor /proc/cpuinfo gives this: processor : 0 processor : 1 But it must be possible because ffmpeg is reported as such in top: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 7018 sean 15 0 309m 236m 1684 R 120 11.7 26:15.29 ffmpeg CPU% is greater than 100 I'm using a stock ubuntu kernel: uname -a: Linux bar 2.6.20-16-generic #2 SMP Thu Jun 7 20:19:32 UTC 2007 i686 GNU/Linux ** Affects: ubuntu Importance: Undecided Status: New -- Multithreading not utilizing both cores https://bugs.launchpad.net/bugs/139631 You received this bug notification because you are a member of Ubuntu Bugs, which is the bug contact for Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
