[PATCH v4 0/4] bpf: Introduce the new ability of eBPF programs to access hardware PMU counter

[Kaixu Xia]

Previous patch v3 url:
https://lkml.org/lkml/2015/7/23/203

changes in V4: 
 - make the bpf_prog_array_map more generic;
 - fix the bug of event refcnt leak;
 - use more useful errno in bpf_perf_event_read();

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 4/4 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
       ...
       syslog-ng-548   [000] d..1    76.905673: : CPU-0   681765271
       syslog-ng-548   [000] d..1    76.905690: : CPU-0   681787855
       syslog-ng-548   [000] d..1    76.905707: : CPU-0   681810504
       syslog-ng-548   [000] d..1    76.905725: : CPU-0   681834771
       syslog-ng-548   [000] d..1    76.905745: : CPU-0   681859519
       syslog-ng-548   [000] d..1    76.905766: : CPU-0   681890419
       syslog-ng-548   [000] d..1    76.905783: : CPU-0   681914045
       syslog-ng-548   [000] d..1    76.905800: : CPU-0   681935950
       syslog-ng-548   [000] d..1    76.905816: : CPU-0   681958299
              ls-690   [005] d..1    82.241308: : CPU-5   3138451
              sh-691   [004] d..1    82.244570: : CPU-4   7324988
           <...>-699   [007] d..1    99.961387: : CPU-7   3194027
           <...>-695   [003] d..1    99.961474: : CPU-3   288901
           <...>-695   [003] d..1    99.961541: : CPU-3   383145
           <...>-695   [003] d..1    99.961591: : CPU-3   450365
           <...>-695   [003] d..1    99.961639: : CPU-3   515751
           <...>-695   [003] d..1    99.961686: : CPU-3   579047
       ...

The detail of patches is as follow:

Patch 1/4 rewrites part of the bpf_prog_array map code and make it
more generic;

Patch 2/4 introduces a new bpf map type. This map only stores the
pointer to struct perf_event;

Patch 3/4 implements function bpf_perf_event_read() that get the
selected hardware PMU conuter;

Patch 4/4 gives 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

Wang Nan (1):
  bpf: Make the bpf_prog_array_map more generic

 include/linux/bpf.h        |   8 ++-
 include/linux/perf_event.h |   5 +-
 include/uapi/linux/bpf.h   |   2 +
 kernel/bpf/arraymap.c      | 161 ++++++++++++++++++++++++++++++++++++---------
 kernel/bpf/helpers.c       |  36 ++++++++++
 kernel/bpf/syscall.c       |   4 +-
 kernel/bpf/verifier.c      |  15 +++++
 kernel/events/core.c       |  21 +++++-
 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 +++++++++++++++++++
 13 files changed, 316 insertions(+), 37 deletions(-)
 create mode 100644 samples/bpf/tracex6_kern.c
 create mode 100644 samples/bpf/tracex6_user.c

-- 
1.8.3.4

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