Previous patch V3 url:
https://lkml.org/lkml/2015/10/16/101
This patchset introduces the new perf_event_attr attribute
'soft_disable'. The already existed 'disabled' flag doesn't
meet the requirements. The cpu_function_call is too much
to do from bpf program and we control the perf_event stored in
maps like soft_disable, so if the 'disabled' flag is set to
true, we can't enable/disable the perf event by bpf programs.
changes in V4:
- make the naming more proper;
- fix the initial value set of attr->soft_disable bug;
- add unlikely() to the check of event->soft_enable;
- squash the 2ed patch into 1st patch;
changes in V3:
- make the flag name and condition check consistent;
- check the bpf helper flag only bit 0 and check all other bits are
reserved;
- use atomic_dec_if_positive() and atomic_inc_unless_negative();
- make bpf_perf_event_dump_control_proto be static;
- remove the ioctl PERF_EVENT_IOC_SET_ENABLER and 'enabler' event;
- implement the function that controlling all the perf events
stored in PERF_EVENT_ARRAY maps by setting the parameter 'index'
to maps max_entries;
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: 527 of event 'cycles'
# Event count (approx.): 87824857
...
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: 22 of event 'cycles'
# Event count (approx.): 4213922
...
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_control(&my_cycles_map, 0, 2);
return 0;
}
SEC("exit=sys_write%return")
int bpf_prog_2(struct pt_regs *ctx)
{
bpf_perf_event_control(&my_cycles_map, 0, 3);
return 0;
}
Consider control sampling in function level, we have to set
a high sample frequency to dump trace data when enable/disable
the perf event on current cpu.
Kaixu Xia (1):
bpf: control events stored in PERF_EVENT_ARRAY maps trace data output
when perf sampling
include/linux/perf_event.h | 1 +
include/uapi/linux/bpf.h | 19 +++++++++++++++
include/uapi/linux/perf_event.h | 3 ++-
kernel/bpf/verifier.c | 3 ++-
kernel/events/core.c | 13 +++++++++++
kernel/trace/bpf_trace.c | 51 +++++++++++++++++++++++++++++++++++++++++
6 files changed, 88 insertions(+), 2 deletions(-)
--
1.8.3.4
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