[PATCH v2 0/5] bpf: Introduce the new ability of eBPF programs to access hardware PMU counter

Kaixu Xia
2015-07-22T08:11:56Z

Previous patch v1 url:
https://lkml.org/lkml/2015/7/17/287

This patchset allows user read PMU events in the following way:
1. Open the PMU using perf_event_open() (for each CPUs or for
each processes he/she'd like to watch);
2. Create a BPF_MAP_TYPE_PERF_EVENT_ARRAY BPF map;
3. Insert FDs into the map with some key-value mapping scheme
(i.e. cpuid -> event on that CPU);
4. Load and attach eBPF programs as usual;
5. In eBPF program, get the perf_event_map_fd and key (i.e.
cpuid get from bpf_get_smp_processor_id()) then use
bpf_perf_event_read() to read from it.
6. Do anything he/her want.

changes in V2:
- put atomic_long_inc_not_zero() between fdget() and fdput();
- limit the event type to PERF_TYPE_RAW and PERF_TYPE_HARDWARE;
- Only read the event counter on current CPU or on current
process;
- add new map type BPF_MAP_TYPE_PERF_EVENT_ARRAY to store the
pointer to the struct perf_event;
- according to the perf_event_map_fd and key, the function
bpf_perf_event_read() can get the Hardware PMU counter value;

Patch 5/5 is a simple example and shows how to use this new eBPF
programs ability. The PMU counter data can be found in
/sys/kernel/debug/tracing/trace(trace_pipe).(the cycles PMU
value when 'kprobe/sys_write' sampling)

$ cat /sys/kernel/debug/tracing/trace_pipe
$ ./tracex6
...
cat-677 [002] d..1 210.299270: : bpf count: CPU-2 5316659
cat-677 [002] d..1 210.299316: : bpf count: CPU-2 5378639
cat-677 [002] d..1 210.299362: : bpf count: CPU-2 5440654
cat-677 [002] d..1 210.299408: : bpf count: CPU-2 5503211
cat-677 [002] d..1 210.299454: : bpf count: CPU-2 5565438
cat-677 [002] d..1 210.299500: : bpf count: CPU-2 5627433
cat-677 [002] d..1 210.299547: : bpf count: CPU-2 5690033
cat-677 [002] d..1 210.299593: : bpf count: CPU-2 5752184
cat-677 [002] d..1 210.299639: : bpf count: CPU-2 5814543
<...>-548 [009] d..1 210.299667: : bpf count: CPU-9 605418074
<...>-548 [009] d..1 210.299692: : bpf count: CPU-9 605452692
cat-677 [002] d..1 210.299700: : bpf count: CPU-2 5896319
<...>-548 [009] d..1 210.299710: : bpf count: CPU-9 605477824
<...>-548 [009] d..1 210.299728: : bpf count: CPU-9 605501726
<...>-548 [009] d..1 210.299745: : bpf count: CPU-9 605525279
<...>-548 [009] d..1 210.299762: : bpf count: CPU-9 605547817
<...>-548 [009] d..1 210.299778: : bpf count: CPU-9 605570433
<...>-548 [009] d..1 210.299795: : bpf count: CPU-9 605592743
...

The detail of patches is as follow:

Patch 1/5 introduces a new bpf map type. This map only stores the
pointer to struct perf_event;

Patch 2/5 introduces a map_traverse_elem() function for further use;

Patch 3/5 convets event file descriptors into perf_event structure when
add new element to the map;

Patch 4/5 implement function bpf_perf_event_read() that get the selected
hardware PMU conuter;

Patch 5/5 give a simple example.

Kaixu Xia (5):
bpf: Add new bpf map type to store the pointer to struct perf_event
bpf: Add function map->ops->map_traverse_elem() to traverse map elems
bpf: Save the pointer to struct perf_event to map
bpf: Implement function bpf_perf_event_read() that get the selected
hardware PMU conuter
samples/bpf: example of get selected PMU counter value

include/linux/bpf.h | 6 +++
include/linux/perf_event.h | 5 ++-
include/uapi/linux/bpf.h | 3 ++
kernel/bpf/arraymap.c | 110 +++++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/helpers.c | 42 +++++++++++++++++
kernel/bpf/syscall.c | 26 +++++++++++
kernel/events/core.c | 30 ++++++++++++-
kernel/trace/bpf_trace.c | 2 +
samples/bpf/Makefile | 4 ++
samples/bpf/bpf_helpers.h | 2 +
samples/bpf/tracex6_kern.c | 27 +++++++++++
samples/bpf/tracex6_user.c | 67 +++++++++++++++++++++++++++
12 files changed, 321 insertions(+), 3 deletions(-)
create mode 100644 samples/bpf/tracex6_kern.c
create mode 100644 samples/bpf/tracex6_user.c

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1.8.3.4