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Subject[RFC PATCH v1 24/37] perf evsel: handle precise_ip fallback in evsel__open_cpu
Date
This is another patch in the effort to separate the fallback mechanisms
from the open itself.

In case of precise_ip fallback, the original precise_ip will be stored
in the evsel (it was stored in a local variable) and the open will be
retried. Since the precise_ip fallback will be the first in the chain of
fallbacks, there should be no functional change with this patch.

Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
---
tools/perf/util/evsel.c | 59 ++++++++++++++++++-----------------------
tools/perf/util/evsel.h | 2 ++
2 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 3e556afed8dd396c..2e95416b8320c6b9 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1709,42 +1709,29 @@ static void display_attr(struct perf_event_attr *attr)
}
}

-static int perf_event_open(struct evsel *evsel,
- pid_t pid, int cpu, int group_fd)
+bool evsel__precise_ip_fallback(struct evsel *evsel)
{
- int precise_ip = evsel->core.attr.precise_ip;
- int fd;
-
- while (1) {
- pr_debug2_peo("sys_perf_event_open: pid %d cpu %d group_fd %d flags %#lx",
- pid, cpu, group_fd, evsel->open_flags);
-
- fd = sys_perf_event_open(&evsel->core.attr, pid, cpu, group_fd, evsel->open_flags);
- if (fd >= 0)
- break;
-
- /* Do not try less precise if not requested. */
- if (!evsel->precise_max)
- break;
-
- /*
- * We tried all the precise_ip values, and it's
- * still failing, so leave it to standard fallback.
- */
- if (!evsel->core.attr.precise_ip) {
- evsel->core.attr.precise_ip = precise_ip;
- break;
- }
+ /* Do not try less precise if not requested. */
+ if (!evsel->precise_max)
+ return false;

- pr_debug2_peo("\nsys_perf_event_open failed, error %d\n", -ENOTSUP);
- evsel->core.attr.precise_ip--;
- pr_debug2_peo("decreasing precise_ip by one (%d)\n", evsel->core.attr.precise_ip);
- display_attr(&evsel->core.attr);
+ /*
+ * We tried all the precise_ip values, and it's
+ * still failing, so leave it to standard fallback.
+ */
+ if (!evsel->core.attr.precise_ip) {
+ evsel->core.attr.precise_ip = evsel->precise_ip_original;
+ return false;
}

- return fd;
-}
+ if (!evsel->precise_ip_original)
+ evsel->precise_ip_original = evsel->core.attr.precise_ip;

+ evsel->core.attr.precise_ip--;
+ pr_debug2_peo("decreasing precise_ip by one (%d)\n", evsel->core.attr.precise_ip);
+ display_attr(&evsel->core.attr);
+ return true;
+}

static struct perf_cpu_map *empty_cpu_map;
static struct perf_thread_map *empty_thread_map;
@@ -2004,8 +1991,11 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,

test_attr__ready();

- fd = perf_event_open(evsel, pid, cpus->map[cpu],
- group_fd);
+ pr_debug2_peo("sys_perf_event_open: pid %d cpu %d group_fd %d flags %#lx",
+ pid, cpus->map[cpu], group_fd, evsel->open_flags);
+
+ fd = sys_perf_event_open(&evsel->core.attr, pid, cpus->map[cpu],
+ group_fd, evsel->open_flags);

FD(evsel, cpu, thread) = fd;

@@ -2058,6 +2048,9 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
return 0;

try_fallback:
+ if (evsel__precise_ip_fallback(evsel))
+ goto retry_open;
+
if (evsel__ignore_missing_thread(evsel, cpus->nr, cpu, threads, thread, err)) {
/* We just removed 1 thread, so lower the upper nthreads limit. */
nthreads--;
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 661d2677a19b6248..0a245afab2d87d74 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -150,6 +150,7 @@ struct evsel {
struct bperf_follower_bpf *follower_skel;
};
unsigned long open_flags;
+ int precise_ip_original;
};

struct perf_missing_features {
@@ -297,6 +298,7 @@ bool evsel__ignore_missing_thread(struct evsel *evsel,
int nr_cpus, int cpu,
struct perf_thread_map *threads,
int thread, int err);
+bool evsel__precise_ip_fallback(struct evsel *evsel);

struct perf_sample;

--
2.31.1
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