Merge "simpleperf: adjust sample_freq based on max_sample_rate file."

3 files changed, 28 insertions, 11 deletions

diff --git a/simpleperf/environment.cpp b/simpleperf/environment.cpp
index 69f7c144..ed161c23 100644
--- a/simpleperf/environment.cpp
+++ b/simpleperf/environment.cpp
@@ -406,23 +406,30 @@ bool CheckPerfEventLimit() {
   return true;
 }
 
-bool CheckSampleFrequency(uint64_t sample_freq) {
-  if (sample_freq == 0) {
-    LOG(ERROR) << "Sample frequency can't be zero.";
-    return false;
-  }
+bool GetMaxSampleFrequency(uint64_t* max_sample_freq) {
   std::string s;
   if (!android::base::ReadFileToString("/proc/sys/kernel/perf_event_max_sample_rate", &s)) {
     PLOG(DEBUG) << "failed to read /proc/sys/kernel/perf_event_max_sample_rate";
-    // Omit the check if perf_event_max_sample_rate doesn't exist.
-    return true;
+    return false;
   }
   s = android::base::Trim(s);
-  uint64_t max_sample_freq;
-  if (!android::base::ParseUint(s.c_str(), &max_sample_freq)) {
+  if (!android::base::ParseUint(s.c_str(), max_sample_freq)) {
     LOG(ERROR) << "failed to parse /proc/sys/kernel/perf_event_max_sample_rate: " << s;
     return false;
   }
+  return true;
+}
+
+bool CheckSampleFrequency(uint64_t sample_freq) {
+  if (sample_freq == 0) {
+    LOG(ERROR) << "Sample frequency can't be zero.";
+    return false;
+  }
+  uint64_t max_sample_freq;
+  if (!GetMaxSampleFrequency(&max_sample_freq)) {
+    // Omit the check if can't read perf_event_max_sample_rate.
+    return true;
+  }
   if (sample_freq > max_sample_freq) {
     LOG(ERROR) << "Sample frequency " << sample_freq << " is out of range [1, "
         << max_sample_freq << "]";
diff --git a/simpleperf/environment.h b/simpleperf/environment.h
index 16df6906..11eee2ff 100644
--- a/simpleperf/environment.h
+++ b/simpleperf/environment.h
@@ -69,6 +69,7 @@ bool GetThreadName(pid_t tid, std::string* name);
 bool GetValidThreadsFromThreadString(const std::string& tid_str, std::set<pid_t>* tid_set);
 
 bool CheckPerfEventLimit();
+bool GetMaxSampleFrequency(uint64_t* max_sample_freq);
 bool CheckSampleFrequency(uint64_t sample_freq);
 bool CheckKernelSymbolAddresses();
 
diff --git a/simpleperf/event_fd.cpp b/simpleperf/event_fd.cpp
index b78da4c0..18eff2d2 100644
--- a/simpleperf/event_fd.cpp
+++ b/simpleperf/event_fd.cpp
@@ -32,6 +32,7 @@
 #include <android-base/logging.h>
 #include <android-base/stringprintf.h>
 
+#include "environment.h"
 #include "event_attr.h"
 #include "event_type.h"
 #include "perf_event.h"
@@ -51,7 +52,15 @@ std::unique_ptr<EventFd> EventFd::OpenEventFile(const perf_event_attr& attr,
   if (group_event_fd != nullptr) {
     group_fd = group_event_fd->perf_event_fd_;
   }
-  int perf_event_fd = perf_event_open(attr, tid, cpu, group_fd, 0);
+  perf_event_attr real_attr = attr;
+  if (attr.freq) {
+    uint64_t max_sample_freq;
+    if (GetMaxSampleFrequency(&max_sample_freq) && max_sample_freq < attr.sample_freq) {
+      PLOG(INFO) << "Adjust sample freq to max allowed sample freq " << max_sample_freq;
+      real_attr.sample_freq = max_sample_freq;
+    }
+  }
+  int perf_event_fd = perf_event_open(real_attr, tid, cpu, group_fd, 0);
   if (perf_event_fd == -1) {
     if (report_error) {
       PLOG(ERROR) << "open perf_event_file (event " << event_name << ", tid "
@@ -77,7 +86,7 @@ std::unique_ptr<EventFd> EventFd::OpenEventFile(const perf_event_attr& attr,
     return nullptr;
   }
   return std::unique_ptr<EventFd>(
-      new EventFd(attr, perf_event_fd, event_name, tid, cpu));
+      new EventFd(real_attr, perf_event_fd, event_name, tid, cpu));
 }
 
 EventFd::~EventFd() {