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

Kaixu Xia
2015-10-14T12:37:55Z

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(-)

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1.8.3.4