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[PATCH V2 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

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  [PATCH V2 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia <xiakaixu@huawei.com> - 2015-10-14 14:40 +0200
    [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER Kaixu Xia <xiakaixu@huawei.com> - 2015-10-14 14:40 +0200
      Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a  new ioctl PERF_EVENT_IOC_SET_ENABLER Alexei Starovoitov <ast@plumgrid.com> - 2015-10-14 23:30 +0200
        Re: [PATCH V2 2/2] bpf: control a set of perf events by creating  a new ioctl PERF_EVENT_IOC_SET_ENABLER xiakaixu <xiakaixu@huawei.com> - 2015-10-15 04:30 +0200

#1246628 — [PATCH V2 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling

Previous RFC patch url:
https://lkml.org/lkml/2015/10/12/135

changes in V2:
 - rebase the whole patch set to net-next tree(4b418bf);
 - remove the added flag perf_sample_disable in bpf_map;
 - move the added fields in structure perf_event to proper place
   to avoid cacheline miss;
 - use counter based flag instead of 0/1 switcher in considering
   of reentering events;
 - use a single helper bpf_perf_event_sample_control() to enable/
   disable events;
 - implement a light-weight solution to control the trace data
   output on current cpu;
 - create a new ioctl PERF_EVENT_IOC_SET_ENABLER to enable/disable
   a set of events;

Before this patch,
   $ ./perf record -e cycles -a sleep 1
   $ ./perf report --stdio
	# To display the perf.data header info, please use --header/--header-only option
	#
	#
	# Total Lost Samples: 0
	#
	# Samples: 643  of event 'cycles'
	# Event count (approx.): 128313904
	...

After this patch,
   $ ./perf record -e pmux=cycles --event perf-bpf.o/my_cycles_map=pmux/ -a sleep 1
   $ ./perf report --stdio
	# To display the perf.data header info, please use --header/--header-only option
	#
	#
	# Total Lost Samples: 0
	#
	# Samples: 25  of event 'cycles'
	# Event count (approx.): 5788400
	...

The bpf program example:

  struct bpf_map_def SEC("maps") my_cycles_map = {
          .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
          .key_size = sizeof(int),
          .value_size = sizeof(u32),
          .max_entries = 32, 
  };

  SEC("enter=sys_write")
  int bpf_prog_1(struct pt_regs *ctx)
  {
          bpf_perf_event_sample_control(&my_cycles_map, 32, 0); 
          return 0;
  }

  SEC("exit=sys_write%return")
  int bpf_prog_2(struct pt_regs *ctx)
  {
          bpf_perf_event_sample_control(&my_cycles_map, 32, 1); 
          return 0;
  }

Consider control sampling in function level, if we don't use the
PERF_EVENT_IOC_SET_ENABLER ioctl in perf user side, we must set
a high sample frequency to dump trace data.

Kaixu Xia (2):
  bpf: control the trace data output on current cpu when perf sampling
  bpf: control a set of perf events by creating a new ioctl
    PERF_EVENT_IOC_SET_ENABLER

 include/linux/perf_event.h      |  2 ++
 include/uapi/linux/bpf.h        |  5 ++++
 include/uapi/linux/perf_event.h |  4 +++-
 kernel/bpf/verifier.c           |  3 ++-
 kernel/events/core.c            | 53 +++++++++++++++++++++++++++++++++++++++++
 kernel/trace/bpf_trace.c        | 35 +++++++++++++++++++++++++++
 6 files changed, 100 insertions(+), 2 deletions(-)

-- 
1.8.3.4

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#1246629 — [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER

This patch creates a new ioctl PERF_EVENT_IOC_SET_ENABLER to let
perf to select an event as 'enabler'. So we can set this 'enabler'
event to enable/disable a set of events. The event on CPU 0 is
treated as the 'enabler' event by default.

Signed-off-by: Kaixu Xia <xiakaixu@huawei.com>
---
 include/linux/perf_event.h      |  1 +
 include/uapi/linux/perf_event.h |  1 +
 kernel/events/core.c            | 42 ++++++++++++++++++++++++++++++++++++++++-
 kernel/trace/bpf_trace.c        |  5 ++++-
 4 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index dcbf7d5..bc9fe77 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -473,6 +473,7 @@ struct perf_event {
 
 	atomic_t			event_limit;
 	atomic_t			sample_disable;
+	atomic_t			*p_sample_disable;
 
 	void (*destroy)(struct perf_event *);
 	struct rcu_head			rcu_head;
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index a2b9dd7..3b4fb90 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -393,6 +393,7 @@ struct perf_event_attr {
 #define PERF_EVENT_IOC_SET_FILTER	_IOW('$', 6, char *)
 #define PERF_EVENT_IOC_ID		_IOR('$', 7, __u64 *)
 #define PERF_EVENT_IOC_SET_BPF		_IOW('$', 8, __u32)
+#define PERF_EVENT_IOC_SET_ENABLER	_IO ('$', 9)
 
 enum perf_event_ioc_flags {
 	PERF_IOC_FLAG_GROUP		= 1U << 0,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 942351c..03d2594 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -4152,6 +4152,7 @@ static int perf_event_set_output(struct perf_event *event,
 				 struct perf_event *output_event);
 static int perf_event_set_filter(struct perf_event *event, void __user *arg);
 static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);
+static int perf_event_set_sample_enabler(struct perf_event *event, u32 enabler_fd);
 
 static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
 {
@@ -4208,6 +4209,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
 	case PERF_EVENT_IOC_SET_BPF:
 		return perf_event_set_bpf_prog(event, arg);
 
+	case PERF_EVENT_IOC_SET_ENABLER:
+		return perf_event_set_sample_enabler(event, arg);
+
 	default:
 		return -ENOTTY;
 	}
@@ -6337,7 +6341,7 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending);
 	}
 
-	if (!atomic_read(&event->sample_disable))
+	if (!atomic_read(event->p_sample_disable))
 		return ret;
 
 	if (event->overflow_handler)
@@ -6989,6 +6993,35 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 	return 0;
 }
 
+static int perf_event_set_sample_enabler(struct perf_event *event, u32 enabler_fd)
+{
+	int ret;
+	struct fd enabler;
+	struct perf_event *enabler_event;
+
+	if (enabler_fd == -1)
+		return 0;
+
+	ret = perf_fget_light(enabler_fd, &enabler);
+	if (ret)
+		return ret;
+	enabler_event = enabler.file->private_data;
+	if (event == enabler_event) {
+		fdput(enabler);
+		return 0;
+	}
+
+	/* they must be on the same PMU*/
+	if (event->pmu != enabler_event->pmu) {
+		fdput(enabler);
+		return -EINVAL;
+	}
+
+	event->p_sample_disable = &enabler_event->sample_disable;
+	fdput(enabler);
+	return 0;
+}
+
 static void perf_event_free_bpf_prog(struct perf_event *event)
 {
 	struct bpf_prog *prog;
@@ -7023,6 +7056,11 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
 	return -ENOENT;
 }
 
+static int perf_event_set_sample_enabler(struct perf_event *event, u32 group_fd)
+{
+	return -ENOENT;
+}
+
 static void perf_event_free_bpf_prog(struct perf_event *event)
 {
 }
@@ -7718,6 +7756,8 @@ static void perf_event_check_sample_flag(struct perf_event *event)
 		atomic_set(&event->sample_disable, 0);
 	else
 		atomic_set(&event->sample_disable, 1);
+
+	event->p_sample_disable = &event->sample_disable;
 }
 
 /*
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f261333..d012be3 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
 	struct bpf_array *array = container_of(map, struct bpf_array, map);
 	struct perf_event *event;
 
-	if (unlikely(index >= array->map.max_entries))
+	if (unlikely(index > array->map.max_entries))
 		return -E2BIG;
 
+	if (index == array->map.max_entries)
+		index = 0;
+
 	event = (struct perf_event *)array->ptrs[index];
 	if (!event)
 		return -ENOENT;
-- 
1.8.3.4

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#1247198 — Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER

On 10/14/15 5:37 AM, Kaixu Xia wrote:
> +	event->p_sample_disable = &enabler_event->sample_disable;

I don't like it as a concept and it's buggy implementation.
What happens here when enabler is alive, but other event is destroyed?

> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
>   	struct bpf_array *array = container_of(map, struct bpf_array, map);
>   	struct perf_event *event;
>
> -	if (unlikely(index >= array->map.max_entries))
> +	if (unlikely(index > array->map.max_entries))
>   		return -E2BIG;
>
> +	if (index == array->map.max_entries)
> +		index = 0;

what is this hack for ?

Either use notification and user space disable or
call bpf_perf_event_sample_control() manually for each cpu.


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#1247345 — Re: [PATCH V2 2/2] bpf: control a set of perf events by creating a new ioctl PERF_EVENT_IOC_SET_ENABLER

于 2015/10/15 5:28, Alexei Starovoitov 写道:
> On 10/14/15 5:37 AM, Kaixu Xia wrote:
>> +    event->p_sample_disable = &enabler_event->sample_disable;
> 
> I don't like it as a concept and it's buggy implementation.
> What happens here when enabler is alive, but other event is destroyed?
> 
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -221,9 +221,12 @@ static u64 bpf_perf_event_sample_control(u64 r1, u64 index, u64 flag, u64 r4, u6
>>       struct bpf_array *array = container_of(map, struct bpf_array, map);
>>       struct perf_event *event;
>>
>> -    if (unlikely(index >= array->map.max_entries))
>> +    if (unlikely(index > array->map.max_entries))
>>           return -E2BIG;
>>
>> +    if (index == array->map.max_entries)
>> +        index = 0;
> 
> what is this hack for ?
> 
> Either use notification and user space disable or
> call bpf_perf_event_sample_control() manually for each cpu.

I will discard current implemention that controlling a set of
perf events by the 'enabler' event. Call bpf_perf_event_sample_control()
manually for each cpu is fine. Maybe we can add a loop to control all the
events stored in maps by judging the index, OK?
> 
> 
> 
> .
> 


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