[PATCH v3 0/3] bpf: Introduce the new ability of eBPF programs to access hardware PMU counter

Kaixu Xia
2015-07-23T09:43:27Z

Previous patch v2 url:
https://lkml.org/lkml/2015/7/22/104

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 index (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 V3:
- collapse V2 patches 1-3 into one;
- drop the function map->ops->map_traverse_elem() and release
the struct perf_event in map_free;
- only allow to access bpf_perf_event_read() from programs;
- update the perf_event_array_map elem via xchg();
- pass index directly to bpf_perf_event_read() instead of
MAP_KEY;

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 3/3 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-674 [000] d..1 146.413405: : CPU-0 2558223
<...>-699 [003] d..1 146.413441: : CPU-3 2663985
cat-674 [000] d..1 146.413480: : CPU-0 2659705
<...>-699 [003] d..1 146.413516: : CPU-3 2765199
cat-674 [000] d..1 146.413555: : CPU-0 2761277
<...>-699 [003] d..1 146.413600: : CPU-3 2877051
cat-674 [000] d..1 146.413651: : CPU-0 2889668
<...>-699 [003] d..1 146.413696: : CPU-3 3006447
cat-674 [000] d..1 146.413749: : CPU-0 3021285
<...>-699 [003] d..1 146.413787: : CPU-3 3131459
cat-674 [000] d..1 146.413838: : CPU-0 3141959
<...>-699 [003] d..1 146.413886: : CPU-3 3264188
cat-674 [000] d..1 146.413930: : CPU-0 3266461
<...>-699 [003] d..1 146.413973: : CPU-3 3381038
cat-674 [000] d..1 146.414025: : CPU-0 3393730
<...>-699 [003] d..1 146.414071: : CPU-3 3514676
...

The detail of patches is as follow:

Patch 1/3 introduces a new bpf map type. This map only stores the
pointer to struct perf_event;

Patch 2/3 implement function bpf_perf_event_read() that get the selected
hardware PMU conuter;

Patch 3/3 give a simple example.

Kaixu Xia (3):
bpf: Add new bpf map type to store the pointer to struct perf_event
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 | 3 ++
include/linux/perf_event.h | 5 +-
include/uapi/linux/bpf.h | 2 +
kernel/bpf/arraymap.c | 113 +++++++++++++++++++++++++++++++++++++++++++++
kernel/bpf/helpers.c | 36 +++++++++++++++
kernel/bpf/verifier.c | 15 ++++++
kernel/events/core.c | 27 ++++++++++-
kernel/trace/bpf_trace.c | 2 +
samples/bpf/Makefile | 4 ++
samples/bpf/bpf_helpers.h | 2 +
samples/bpf/tracex6_kern.c | 26 +++++++++++
samples/bpf/tracex6_user.c | 67 +++++++++++++++++++++++++++
12 files changed, 299 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