Messages in this thread | | | Date | Mon, 20 Apr 2015 16:46:16 -0400 | From | Steven Rostedt <> | Subject | Re: perf/tracepoints access to interpreted strings |
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On Wed, 15 Apr 2015 15:09:27 -0300 Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> Em Wed, Apr 15, 2015 at 10:20:08AM -0600, David Ahern escreveu: > > 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()? > > We'll gonna have to parse the "print fmt" thing and look for entries > surrounded by [], then match it with the list of parameters, so that we > can end up with a: > > const char *perf_evsel__enum_entry(struct perf_evsel *evsel, > struct perf_sample *sample, > const char *enum_name, > int value); > > That would return one of "TIMER", "NET_TX", etc, that is, 0, > 1, N. > > If it is strictly an enum, i.e. no holes and just by looking at the > "format" file above I don't see how it could have holes, albeit enums > may have, we can as well have this: > > const char *perf_evsel__enum(struct perf_evsel *evsel, > struct perf_sample *sample, > const char *enum_name); > > That would return an array of strings that you could directly access, > indexing using some of the fields. > > I.e. internally we would see the tracepoint format file as: > > field:enum action vec; offset:12; size:4; signed:0; > > enum: action: TIMER, NET_TX, NET_RX, BLOCK, BLOCK_IOPOLL, TASKLET, SCHED, HRTIMER, RCU >
Note, with the new TRACE_DEFINE_ENUM() that was already added to Linus's tree, that print_fmt now looks like:
print fmt: "vec=%u [action=%s]", REC->vec, __print_symbolic(REC->vec, { 0, "HI" }, { 1, "TIMER" }, { 2, "NET_TX" }, { 3, "NET_RX" }, { 4, "BLOCK" }, { 5, "BLOCK_IOPOLL" }, { 6, "TASKLET" }, { 7, "SCHED" }, { 8, "HRTIMER" }, { 9, "RCU" })
-- Steve
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