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SubjectRe: [PATCH v2 9/9] perf probe: Support SDT markers having reference counter (semaphore)
Hi Ravi,

On Wed, 4 Apr 2018 14:01:10 +0530
Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> wrote:

> With this, perf buildid-cache will save SDT markers with reference
> counter in probe cache. Perf probe will be able to probe markers
> having reference counter. Ex,
>
> # readelf -n /tmp/tick | grep -A1 loop2
> Name: loop2
> ... Semaphore: 0x0000000010020036
>
> # ./perf buildid-cache --add /tmp/tick
> # ./perf probe sdt_tick:loop2
> # ./perf stat -e sdt_tick:loop2 /tmp/tick
> hi: 0
> hi: 1
> hi: 2
> ^C
> Performance counter stats for '/tmp/tick':
> 3 sdt_tick:loop2
> 2.561851452 seconds time elapsed
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
> ---
> tools/perf/util/probe-event.c | 18 ++++++++++++++---
> tools/perf/util/probe-event.h | 1 +
> tools/perf/util/probe-file.c | 34 ++++++++++++++++++++++++++------
> tools/perf/util/probe-file.h | 1 +
> tools/perf/util/symbol-elf.c | 46 ++++++++++++++++++++++++++++++++-----------
> tools/perf/util/symbol.h | 7 +++++++
> 6 files changed, 86 insertions(+), 21 deletions(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index e1dbc98..b3a1330 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1832,6 +1832,12 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
> tp->offset = strtoul(fmt2_str, NULL, 10);
> }
>
> + if (tev->uprobes) {
> + fmt2_str = strchr(p, '(');
> + if (fmt2_str)
> + tp->ref_ctr_offset = strtoul(fmt2_str + 1, NULL, 0);
> + }
> +
> tev->nargs = argc - 2;
> tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
> if (tev->args == NULL) {
> @@ -2054,15 +2060,21 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> }
>
> /* Use the tp->address for uprobes */
> - if (tev->uprobes)
> + if (tev->uprobes) {
> err = strbuf_addf(&buf, "%s:0x%lx", tp->module, tp->address);
> - else if (!strncmp(tp->symbol, "0x", 2))
> + if (uprobe_ref_ctr_is_supported() &&
> + tp->ref_ctr_offset &&
> + err >= 0)
> + err = strbuf_addf(&buf, "(0x%lx)", tp->ref_ctr_offset);

If the kernel doesn't support uprobe_ref_ctr but the event requires
to increment uprobe_ref_ctr, I think we should (at least) warn user here.

> + } else if (!strncmp(tp->symbol, "0x", 2)) {
> /* Absolute address. See try_to_find_absolute_address() */
> err = strbuf_addf(&buf, "%s%s0x%lx", tp->module ?: "",
> tp->module ? ":" : "", tp->address);
> - else
> + } else {
> err = strbuf_addf(&buf, "%s%s%s+%lu", tp->module ?: "",
> tp->module ? ":" : "", tp->symbol, tp->offset);
> + }
> +
> if (err)
> goto error;
>
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 45b14f0..15a98c3 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -27,6 +27,7 @@ struct probe_trace_point {
> char *symbol; /* Base symbol */
> char *module; /* Module name */
> unsigned long offset; /* Offset from symbol */
> + unsigned long ref_ctr_offset; /* SDT reference counter offset */
> unsigned long address; /* Actual address of the trace point */
> bool retprobe; /* Return probe flag */
> };
> diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
> index 4ae1123..ca0e524 100644
> --- a/tools/perf/util/probe-file.c
> +++ b/tools/perf/util/probe-file.c
> @@ -697,8 +697,16 @@ int probe_cache__add_entry(struct probe_cache *pcache,
> #ifdef HAVE_GELF_GETNOTE_SUPPORT
> static unsigned long long sdt_note__get_addr(struct sdt_note *note)
> {
> - return note->bit32 ? (unsigned long long)note->addr.a32[0]
> - : (unsigned long long)note->addr.a64[0];
> + return note->bit32 ?
> + (unsigned long long)note->addr.a32[SDT_NOTE_IDX_LOC] :
> + (unsigned long long)note->addr.a64[SDT_NOTE_IDX_LOC];
> +}
> +
> +static unsigned long long sdt_note__get_ref_ctr_offset(struct sdt_note *note)
> +{
> + return note->bit32 ?
> + (unsigned long long)note->addr.a32[SDT_NOTE_IDX_REFCTR] :
> + (unsigned long long)note->addr.a64[SDT_NOTE_IDX_REFCTR];
> }
>
> static const char * const type_to_suffix[] = {
> @@ -776,14 +784,21 @@ static char *synthesize_sdt_probe_command(struct sdt_note *note,
> {
> struct strbuf buf;
> char *ret = NULL, **args;
> - int i, args_count;
> + int i, args_count, err;
> + unsigned long long ref_ctr_offset;
>
> if (strbuf_init(&buf, 32) < 0)
> return NULL;
>
> - if (strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
> - sdtgrp, note->name, pathname,
> - sdt_note__get_addr(note)) < 0)
> + err = strbuf_addf(&buf, "p:%s/%s %s:0x%llx",
> + sdtgrp, note->name, pathname,
> + sdt_note__get_addr(note));
> +
> + ref_ctr_offset = sdt_note__get_ref_ctr_offset(note);
> + if (uprobe_ref_ctr_is_supported() && ref_ctr_offset && err >= 0)
> + err = strbuf_addf(&buf, "(0x%llx)", ref_ctr_offset);

We don't have to care about uprobe_ref_ctr support here, because
this information will be just cached, not directly written to
uprobe_events.

Other parts look good to me.

Thanks,

--
Masami Hiramatsu <mhiramat@kernel.org>

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