From: Frederic Weisbecker <fweisbec@gmail.com>
To: Michael Neuling <mikey@neuling.org>
Cc: K Prasad <prasad@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: powerpc/perf: hw breakpoints return ENOSPC
Date: Fri, 17 Aug 2012 18:15:57 +0200 [thread overview]
Message-ID: <20120817161554.GA3772@somewhere> (raw)
In-Reply-To: <28857.1345091034@neuling.org>
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;
>
next prev parent reply other threads:[~2012-08-17 16:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-16 4:23 powerpc/perf: hw breakpoints return ENOSPC Michael Neuling
2012-08-16 7:40 ` Peter Zijlstra
2012-08-16 11:17 ` Michael Neuling
2012-08-16 11:44 ` Peter Zijlstra
2012-08-16 14:02 ` Michael Ellerman
2012-08-16 14:15 ` Peter Zijlstra
2012-08-17 1:20 ` Michael Ellerman
2012-08-16 23:34 ` Michael Neuling
2012-08-17 16:15 ` Frederic Weisbecker [this message]
2012-08-17 21:58 ` Michael Neuling
2012-09-25 7:10 ` Michael Neuling
2012-09-27 15:23 ` Frederic Weisbecker
2012-09-27 1:02 ` Jovi Zhang
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