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Allow for collection of more PMUs than are physically available. #1737

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Allow for collection of more PMUs than are physically available. #1737

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36 changes: 22 additions & 14 deletions src/perf_counters.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -86,6 +86,12 @@ PerfCounters PerfCounters::Create(
Initialize();
}

// Initially try to create a single group which holds all PMUs since that
// has lower overhead. Group multiplexing doesn't work on all platforms so if
// that fails try again without using groups.
bool group_pmus = true;
retry_without_groups:
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maybe extracting this into a separate method and calling it with group_pmus as a parameter (and having a return value to indicate whether retry should happen) would be cleaner than a goto


// Valid counters will populate these arrays but we start empty
std::vector<std::string> valid_names;
std::vector<int> counter_ids;
Expand All @@ -96,11 +102,6 @@ PerfCounters PerfCounters::Create(
counter_ids.reserve(counter_names.size());

const int kCounterMode = PFM_PLM3; // user mode only

// Group leads will be assigned on demand. The idea is that once we cannot
// create a counter descriptor, the reason is that this group has maxed out
// so we set the group_id again to -1 and retry - giving the algorithm a
// chance to create a new group leader to hold the next set of counters.
int group_id = -1;

// Loop through all performance counters
Expand Down Expand Up @@ -150,7 +151,7 @@ PerfCounters PerfCounters::Create(
// case.
attr.disabled = is_first;
attr.inherit = true;
attr.pinned = is_first;
attr.pinned = group_pmus;
attr.exclude_kernel = true;
attr.exclude_user = false;
attr.exclude_hv = true;
Expand All @@ -171,10 +172,14 @@ PerfCounters PerfCounters::Create(
}
if (id < 0) {
// If the file descriptor is negative we might have reached a limit
// in the current group. Set the group_id to -1 and retry
if (group_id >= 0) {
// Create a new group
group_id = -1;
// in the current group. Let's try again without groups.
if (group_id >= 0 && group_pmus) {
// Close all performance counters
for (int close_id : counter_ids) {
::close(close_id);
}
group_pmus = false;
goto retry_without_groups;
} else {
// At this point we have already retried to set a new group id and
// failed. We then give up.
Expand All @@ -197,7 +202,9 @@ PerfCounters PerfCounters::Create(
if (group_id < 0) {
// This is a leader, store and assign it to the current file descriptor
leader_ids.push_back(id);
group_id = id;
if (group_pmus) {
group_id = id;
}
}
// This is a valid counter, add it to our descriptor's list
counter_ids.push_back(id);
Expand All @@ -214,9 +221,9 @@ PerfCounters PerfCounters::Create(
// This should never happen but if it does, we give up on the
// entire batch as recovery would be a mess.
GetErrorLogInstance() << "***WARNING*** Failed to start counters. "
"Claring out all counters.\n";
"Clearing out all counters.\n";

// Close all peformance counters
// Close all performance counters
for (int id : counter_ids) {
::close(id);
}
Expand Down Expand Up @@ -254,7 +261,7 @@ bool PerfCounters::IsCounterSupported(const std::string&) { return false; }
PerfCounters PerfCounters::Create(
const std::vector<std::string>& counter_names) {
if (!counter_names.empty()) {
GetErrorLogInstance() << "Performance counters not supported.\n";
GetErrorLogInstance() << "Performance counters not supported.";
}
return NoCounters();
}
Expand All @@ -280,3 +287,4 @@ PerfCounters& PerfCounters::operator=(PerfCounters&& other) noexcept {
}
} // namespace internal
} // namespace benchmark

2 changes: 1 addition & 1 deletion src/perf_counters.h
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,7 @@ class BENCHMARK_EXPORT PerfCounterValues {
}

// This reading is complex and as the goal of this class is to
// abstract away the intrincacies of the reading process, this is
// abstract away the intricacies of the reading process, this is
// a better place for it
size_t Read(const std::vector<int>& leaders);

Expand Down