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    perf, powerpc: Fix hw breakpoints returning -ENOSPC · 0d855354
    Michael Neuling 提交于
    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.
    Signed-off-by: NMichael Neuling <mikey@neuling.org>
    Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Michael Ellerman <michael@ellerman.id.au>
    Cc: Jovi Zhang <bookjovi@gmail.com>
    Cc: K Prasad <prasad@linux.vnet.ibm.com>
    Link: http://lkml.kernel.org/r/1351268936-2956-1-git-send-email-fweisbec@gmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>
    0d855354
hw_breakpoint.c 16.1 KB