On Thu, 2012-08-16 at 14:23 +1000, Michael Neuling wrote:
=20
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=3D1), 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...