On Thu, Aug 16, 2012 at 12:23 PM, Michael Neuling <mi...@neuling.org> wrote: > Hi, > > I've been trying to get hardware breakpoints with perf to work on POWER7 > but I'm getting the following: > > % perf record -e mem:0x10000000 true > > Error: sys_perf_event_open() syscall returned with 28 (No space left on > device). /bin/dmesg may provide additional information. > > Fatal: No CONFIG_PERF_EVENTS=y kernel support configured? > > true: Terminated > > (FWIW adding -a and it works fine) > > Debugging it seems that __reserve_bp_slot() is returning ENOSPC because > it thinks there are no free breakpoint slots on this CPU. > > I have a 2 CPUs, so perf userspace is doing two perf_event_open syscalls > to add a counter to each CPU [1]. The first syscall succeeds but the > second is failing. > > On this second syscall, fetch_bp_busy_slots() sets slots.pinned to be 1, > despite there being no breakpoint on this CPU. This is because the call > the task_bp_pinned, checks all CPUs, rather than just the current CPU. > POWER7 only has one hardware breakpoint per CPU (ie. HBP_NUM=1), so we > return ENOSPC. > > The following patch fixes this by checking the associated CPU for each > breakpoint in task_bp_pinned. I'm not familiar with this code, so it's > provided as a reference to the above issue. > > Mikey > > 1. not sure why it doesn't just do one syscall and specify all CPUs, but > that's another issue. Using two syscalls should work. > This problem let me recall what I reported several months ago.
https://lkml.org/lkml/2012/6/27/631 At that time, I thought it is caused by uses_mmap field in record sub command which added by commit d1cb9f(perf target: Add uses_mmap field). In that testcase, it's fine to use stat sub command, but failed with record sub command. As Namhyung metioned in that thread, [perf record xxx] use per-task-per-cpu for fix scalability issues. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
