On Thu, 2012-08-16 at 21:17 +1000, Michael Neuling wrote: > 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.
ptrace uses perf for hwbp support so we're stuck with all kinds of stupid ptrace constraints.. or somesuch. > Are you saying that we need to keep at least 1 slot free at all times, > so that we can use it for ptrace? No, I'm saying perf-hwbp is weird because of ptrace, maybe the ptrace weirdness shouldn't live in perf-hwpb but in the ptrace-perf glue however.. > Is "perf record -e mem:0x10000000 true" ever going to be able to work on > POWER7 with only one hw breakpoint resource per CPU? I think it should work... but I'm fairly sure it currently doesn't because of how things are done. 'perf record -ie mem:0x100... true' might just work. I always forget all the ptrace details but I am forever annoyed at the mess that is perf-hwbp.. Frederic is there really nothing we can do about this? The fact that ptrace hwbp semantics are different per architecture doesn't help of course. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev