Peter, > > 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. > > I think this comes from the ptrace legacy, we register a breakpoint on > all cpus because when we migrate a task it cannot fail to migrate the > breakpoint. > > Its one of the things I hate most about the hwbp stuff as it relates to > perf. > > Frederic knows more...
Maybe I should wait for Frederic to respond but I'm not sure I understand what you're saying. I can see how using ptrace hw breakpoints and perf hw breakpoints at the same time could be a problem, but I'm not sure how this would stop it. Are you saying that we need to keep at least 1 slot free at all times, so that we can use it for ptrace? Is "perf record -e mem:0x10000000 true" ever going to be able to work on POWER7 with only one hw breakpoint resource per CPU? Thanks, Mikey _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
