Messages in this thread | | | From | Michael Neuling <> | Subject | Re: powerpc/perf: hw breakpoints return ENOSPC | Date | Fri, 17 Aug 2012 09:34:07 +1000 |
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> > > > 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.
OK
> > 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..
OK.
> > 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.
Adding -i doesn't help.
Mikey
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