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Date: Sat, 18 Aug 2012 07:58:15 +1000 From: Michael Neuling <mikey@...ling.org> To: Frederic Weisbecker <fweisbec@...il.com> cc: K Prasad <prasad@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...nel.org> Subject: Re: powerpc/perf: hw breakpoints return ENOSPC Frederic Weisbecker <fweisbec@...il.com> wrote: > 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 ? Of course... Signed-off-by: Michael Neuling <mikey@...ling.org> > > 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; > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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