Hi, all. I want to draw off-cpu flamegraph using perf script on centos6.7 (kernel version, 2.6.32-573), and I found perf script lacks the period data column on that version. I found two related patches, and modifed builin-script.c in reference to those patches. perf script:Add period data column authorJiri Olsa 2014-08-25 16:45:42 +0200 commit535aeaae7de821ba5d43ee2a204ee667ca95aae4 perf script: Add period as a default output column commite8564b710c6df2c3aeb56c507c22f4bcfa4c0b2d)
I used the new complied perf to record some hardware event, like cycles, and the result displays the period data column. But when I record some tracepoint events, like sched:sched_stat_sleep, sched:sched_switch, I found the period data column is always 1. I checked the code(kernel/event/core.c), and found that the data->period is assigned nr in the function named perf_swevent_event. I tracked this function, and found the function call flow: perf_trace_buf_submit--->perf_tp_event---->perf_swevent_event. The function perf_trace_buf_submit is in the ftrace_event.h files, so the period data column for tracepoint events is calulated in the frace subsystem? What is the real meaning of the period field and how to calculate it ? Can you give me some tips for poring this field on the old kernel? Thanks, Wind Yu.
