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damageboydamageboy
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Dynamically detect PMU capabilities through libpfm
- Instead of allowing for up to 3 counters, libpfm's internal capabilities of reporting PMU info are used to manage a per-PMU "registry" adn dynamically allocate slots according to the specific counter requested - In this PR/commit, it is still impossible to get more detailed (x86) information about each specific counter properties in terms of being a fixed/non-fixed counter, due to what seems to be a lack of API surface on libpfm itself: https://sourceforge.net/p/perfmon2/mailman/message/37631173/ - The maximal number of counters was bumped from 3 to 63, which together with the current padding "scheme" means we pre-allocate 64 in-place counter slots (64-bits each) per measurement instance - Closes #1377
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‎src/perf_counters.cc

+125-20
Original file line numberDiff line numberDiff line change
@@ -26,9 +26,121 @@
2626
namespace benchmark {
2727
namespace internal {
2828

29-
constexpr size_t PerfCounterValues::kMaxCounters;
30-
3129
#if defined HAVE_LIBPFM
30+
31+
class SinglePMURegistry {
32+
public:
33+
~SinglePMURegistry() = default;
34+
SinglePMURegistry(SinglePMURegistry&&) = default;
35+
SinglePMURegistry(const SinglePMURegistry&) = delete;
36+
SinglePMURegistry& operator=(SinglePMURegistry&&) noexcept;
37+
SinglePMURegistry& operator=(const SinglePMURegistry&) = delete;
38+
39+
SinglePMURegistry(pfm_pmu_t pmu_id)
40+
: pmu_id_(pmu_id), available_counters_(0), available_fixed_counters_(0) {
41+
{
42+
pfm_pmu_info_t pmu_info{};
43+
const auto pfm_pmu = pfm_get_pmu_info(pmu_id, &pmu_info);
44+
45+
if (pfm_pmu != PFM_SUCCESS) {
46+
GetErrorLogInstance() << "Unknown pmu: " << pmu_id << "\n";
47+
return;
48+
}
49+
50+
name_ = pmu_info.name;
51+
desc_ = pmu_info.desc;
52+
available_counters_ = pmu_info.num_cntrs;
53+
available_fixed_counters_ = pmu_info.num_fixed_cntrs;
54+
55+
BM_VLOG(1) << "PMU: " << pmu_id << " " << name_ << " " << desc_ << "\n";
56+
BM_VLOG(1) << " counters: " << available_counters_ << " fixed: " << available_fixed_counters_ << "\n";
57+
}
58+
}
59+
60+
const char* name() const { return name_; }
61+
62+
bool AddCounter(int event_id) {
63+
pfm_event_info_t info{};
64+
const auto pfm_event_info =
65+
pfm_get_event_info(event_id, PFM_OS_PERF_EVENT, &info);
66+
67+
if (pfm_event_info != PFM_SUCCESS) {
68+
GetErrorLogInstance() << "Unknown event id: " << event_id << "\n";
69+
return false;
70+
}
71+
72+
assert(info.pmu == pmu_id_);
73+
74+
if (counter_ids_.find(event_id) != counter_ids_.end()) return true;
75+
76+
if (counter_ids_.size() >= available_counters_ - 1) {
77+
GetErrorLogInstance() << "Maximal number of counters for PMU " << name_
78+
<< " (" << available_counters_ << ") reached.\n";
79+
return false;
80+
}
81+
82+
counter_ids_.emplace(event_id, info.code);
83+
84+
BM_VLOG(2) << "Registered counter: " << event_id << " (" << info.name << " - " << info.desc
85+
<< ") in pmu " << name_ << " (" << counter_ids_.size() << "/" << available_counters_ << "\n";
86+
87+
return true;
88+
}
89+
90+
private:
91+
pfm_pmu_t pmu_id_;
92+
const char* name_;
93+
const char* desc_;
94+
std::unordered_map<int, uint64_t> counter_ids_;
95+
std::unordered_map<int, uint64_t> fixed_counter_ids_;
96+
uint64_t available_counters_;
97+
uint64_t available_fixed_counters_;
98+
};
99+
100+
class PMURegistry {
101+
public:
102+
~PMURegistry() = default;
103+
PMURegistry(PMURegistry&&) = default;
104+
PMURegistry(const PMURegistry&) = delete;
105+
PMURegistry& operator=(PMURegistry&&) noexcept;
106+
PMURegistry& operator=(const PMURegistry&) = delete;
107+
PMURegistry() {}
108+
109+
bool EnlistCounter(const std::basic_string<char>& name, struct perf_event_attr &attr_base) {
110+
attr_base.size = sizeof(attr_base);
111+
pfm_perf_encode_arg_t encoding{};
112+
encoding.attr = &attr_base;
113+
114+
const auto pfm_get = pfm_get_os_event_encoding(
115+
name.c_str(), PFM_PLM3, PFM_OS_PERF_EVENT, &encoding);
116+
if (pfm_get != PFM_SUCCESS) {
117+
GetErrorLogInstance() << "Unknown counter name: " << name << "\n";
118+
return false;
119+
}
120+
121+
pfm_event_info_t info{};
122+
const auto pfm_info =
123+
pfm_get_event_info(encoding.idx, PFM_OS_PERF_EVENT, &info);
124+
if (pfm_info != PFM_SUCCESS) {
125+
GetErrorLogInstance()
126+
<< "Unknown counter idx: " << encoding.idx << "(" << name << ")\n";
127+
return false;
128+
}
129+
130+
// Spin-up a new per-PMU sub-registry if needed
131+
if (pmu_registry_.find(info.pmu) == pmu_registry_.end()) {
132+
pmu_registry_.emplace(info.pmu, SinglePMURegistry(info.pmu));
133+
}
134+
135+
auto& single_pmu = pmu_registry_.find(info.pmu)->second;
136+
137+
return single_pmu.AddCounter(info.idx);
138+
}
139+
140+
private:
141+
std::unordered_map<pfm_pmu_t, SinglePMURegistry> pmu_registry_;
142+
};
143+
32144
const bool PerfCounters::kSupported = true;
33145

34146
bool PerfCounters::Initialize() { return pfm_initialize() == PFM_SUCCESS; }
@@ -38,35 +150,28 @@ PerfCounters PerfCounters::Create(
38150
if (counter_names.empty()) {
39151
return NoCounters();
40152
}
41-
if (counter_names.size() > PerfCounterValues::kMaxCounters) {
42-
GetErrorLogInstance()
43-
<< counter_names.size()
44-
<< " counters were requested. The minimum is 1, the maximum is "
45-
<< PerfCounterValues::kMaxCounters << "\n";
46-
return NoCounters();
47-
}
153+
48154
std::vector<int> counter_ids(counter_names.size());
155+
PMURegistry registry{};
49156

50-
const int mode = PFM_PLM3; // user mode only
51157
for (size_t i = 0; i < counter_names.size(); ++i) {
52-
const bool is_first = i == 0;
53-
struct perf_event_attr attr {};
54-
attr.size = sizeof(attr);
55-
const int group_id = !is_first ? counter_ids[0] : -1;
56158
const auto& name = counter_names[i];
57159
if (name.empty()) {
58160
GetErrorLogInstance() << "A counter name was the empty string\n";
59161
return NoCounters();
60162
}
61-
pfm_perf_encode_arg_t arg{};
62-
arg.attr = &attr;
63163

64-
const int pfm_get =
65-
pfm_get_os_event_encoding(name.c_str(), mode, PFM_OS_PERF_EVENT, &arg);
66-
if (pfm_get != PFM_SUCCESS) {
67-
GetErrorLogInstance() << "Unknown counter name: " << name << "\n";
164+
struct perf_event_attr attr {};
165+
auto ok = registry.EnlistCounter(name, attr);
166+
167+
if (!ok) {
168+
GetErrorLogInstance() << "Failed to register counter: " << name << "\n";
68169
return NoCounters();
69170
}
171+
172+
const bool is_first = i == 0;
173+
const int group_id = !is_first ? counter_ids[0] : -1;
174+
70175
attr.disabled = is_first;
71176
// Note: the man page for perf_event_create suggests inerit = true and
72177
// read_format = PERF_FORMAT_GROUP don't work together, but that's not the

‎src/perf_counters.h

+7-5
Original file line numberDiff line numberDiff line change
@@ -49,13 +49,15 @@ namespace internal {
4949
// operator[]) of this object.
5050
class PerfCounterValues {
5151
public:
52-
explicit PerfCounterValues(size_t nr_counters) : nr_counters_(nr_counters) {
53-
BM_CHECK_LE(nr_counters_, kMaxCounters);
52+
explicit PerfCounterValues(size_t nr_counters)
53+
: //values_(nr_counters + kPadding),
54+
nr_counters_(nr_counters)
55+
{
56+
BM_CHECK_LE(nr_counters_, kMaxPreAllocatedCounters);
5457
}
55-
5658
uint64_t operator[](size_t pos) const { return values_[kPadding + pos]; }
5759

58-
static constexpr size_t kMaxCounters = 3;
60+
static constexpr size_t kMaxPreAllocatedCounters = 63;
5961

6062
private:
6163
friend class PerfCounters;
@@ -67,7 +69,7 @@ class PerfCounterValues {
6769
}
6870

6971
static constexpr size_t kPadding = 1;
70-
std::array<uint64_t, kPadding + kMaxCounters> values_;
72+
std::array<uint64_t, kPadding + kMaxPreAllocatedCounters> values_;
7173
const size_t nr_counters_;
7274
};
7375

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