perf/tracepoints access to interpreted strings

David Ahern
2015-04-15T16:20:17Z

Hi Steve:

I was hoping you could provide points on how to get access to an
interpreted field in a tracepoint within perf.

This is an example of the tracepoint:

# cat /sys/kernel/debug/tracing/events/irq/softirq_exit/format
name: softirq_exit
ID: 99
format:
field:unsigned short common_type; offset:0; size:2; signed:0;
field:unsigned char common_flags; offset:2; size:1; signed:0;
field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
field:int common_pid; offset:4; size:4; signed:1;
field:int common_padding; offset:8; size:4; signed:1;

field:unsigned int vec; offset:12; size:4; signed:0;

print fmt: "vec=%u [action=%s]", REC->vec, __print_symbolic(REC->vec, {
HI_SOFTIRQ, "HI" }, { TIMER_SOFTIRQ, "TIMER" }, { NET_TX_SOFTIRQ,
"NET_TX" }, { NET_RX_SOFTIRQ, "NET_RX" }, { BLOCK_SOFTIRQ, "BLOCK" }, {
BLOCK_IOPOLL_SOFTIRQ, "BLOCK_IOPOLL" }, { TASKLET_SOFTIRQ, "TASKLET" },
{ SCHED_SOFTIRQ, "SCHED" }, { HRTIMER_SOFTIRQ, "HRTIMER" }, {
RCU_SOFTIRQ, "RCU" })

I would like to programmatically extract the action string. 'perf
script' prints the samples fine which suggests libtraceevent extracts
the information somehow.

Can you provide a suggestion -- something along the lines of
perf_evsel__intval() or perf_evsel__rawptr()?

Thanks,
David