Re: [Question] How to sample PERF_TYPE_HARDWARE

[rainkin <rainkin1993@gmail.com>]

Hi Namhyung,
Thanks for your reply.
Let me make my goal more clear: record the number of occurring branch
instructions (PERF_COUNT_HW_BRANCH_INSTRUCTIONS) every N cycles
(PERF_COUNT_HW_CPU_CYCLES).

For the command you mentioned : perf record -e branches -c N

I use strace to capture the syscall invoked by the above command:

perf_event_open({type=PERF_TYPE_HARDWARE, size=PERF_ATTR_SIZE_VER6,
config=PERF_COUNT_HW_BRANCH_INSTRUCTIONS, sample_period=100000,
sample_type=PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_ID|PERF_SAMPLE_CPU,
read_format=PERF_FORMAT_ID, disabled=1, inherit=1, pinned=0,
exclusive=0, exclusive_user=0, exclude_kernel=0, exclude_hv=0,
exclude_idle=0, mmap=0, comm=0, freq=0, inherit_stat=0,
enable_on_exec=0, task=0, watermark=0, precise_ip=0 /* arbitrary skid
*/, mmap_data=0, sample_id_all=1, exclude_host=0, exclude_guest=1,
exclude_callchain_kernel=0, exclude_callchain_user=0, mmap2=0,
comm_exec=0, use_clockid=0, context_switch=0, write_backward=0,
namespaces=0, wakeup_events=0, config1=0, config2=0,
sample_regs_user=0, sample_regs_intr=0, aux_watermark=0,
sample_max_stack=0, aux_sample_size=0}, -1, 10, -1,
PERF_FLAG_FD_CLOEXEC)

In my understanding ,WHAT this command actually does is recording
IP,TID, and so on
(sample_type=PERF_SAMPLE_IP|PERF_SAMPLE_TID|PERF_SAMPLE_TIME|PERF_SAMPLE_ID|PERF_SAMPLE_CPU)
every N (here N = 100000) branches
(config=PERF_COUNT_HW_BRANCH_INSTRUCTIONS). Thus this cannot meet my
goal.

Thanks,
Rainkin