On Thu, Aug 16, 2012 at 02:23:54PM +1000, Michael Neuling wrote:
> Hi,
>
> 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.
>
> Mikey
>
> 1. not sure why it doesn't just do one syscall and specify all CPUs, but
> that's another issue. Using two syscalls should work.
This patch seems to make sense. I'll try it and run some tests.
Can I have your Signed-off-by ?
Thanks.
>
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index bb38c4d..e092daa 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -111,14 +111,16 @@ static unsigned int max_task_bp_pinned(int cpu, enum
> bp_type_idx type)
> * Count the number of breakpoints of the same type and same task.
> * The given event must be not on the list.
> */
> -static int task_bp_pinned(struct perf_event *bp, enum bp_type_idx type)
> +static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx
> type)
> {
> struct task_struct *tsk = bp->hw.bp_target;
> struct perf_event *iter;
> int count = 0;
>
> list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
> - if (iter->hw.bp_target == tsk && find_slot_idx(iter) == type)
> + if (iter->hw.bp_target == tsk &&
> + find_slot_idx(iter) == type &&
> + cpu == iter->cpu)
> count += hw_breakpoint_weight(iter);
> }
>
> @@ -141,7 +143,7 @@ fetch_bp_busy_slots(struct bp_busy_slots *slots, struct
> perf_event *bp,
> if (!tsk)
> slots->pinned += max_task_bp_pinned(cpu, type);
> else
> - slots->pinned += task_bp_pinned(bp, type);
> + slots->pinned += task_bp_pinned(cpu, bp, type);
> slots->flexible = per_cpu(nr_bp_flexible[type], cpu);
>
> return;
> @@ -154,7 +156,7 @@ fetch_bp_busy_slots(struct bp_busy_slots *slots, struct
> perf_event *bp,
> if (!tsk)
> nr += max_task_bp_pinned(cpu, type);
> else
> - nr += task_bp_pinned(bp, type);
> + nr += task_bp_pinned(cpu, bp, type);
>
> if (nr > slots->pinned)
> slots->pinned = nr;
> @@ -188,7 +190,7 @@ static void toggle_bp_task_slot(struct perf_event *bp,
> int cpu, bool enable,
> int old_idx = 0;
> int idx = 0;
>
> - old_count = task_bp_pinned(bp, type);
> + old_count = task_bp_pinned(cpu, bp, type);
> old_idx = old_count - 1;
> idx = old_idx + weight;
>
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
