From 0d855354ea351bec6b222e9fea86a876cfafdcb6 Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Fri, 26 Oct 2012 18:28:56 +0200 Subject: [PATCH] perf, powerpc: Fix hw breakpoints returning -ENOSPC 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: Michael Neuling Acked-by: Peter Zijlstra Cc: Michael Ellerman Cc: Jovi Zhang Cc: K Prasad Link: http://lkml.kernel.org/r/1351268936-2956-1-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- kernel/events/hw_breakpoint.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c index 9a7b487c6fe2..fe8a916507ed 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;