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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" and dynamically allocate "slots" according to the specific counters requested. - per-PMU information is obtained, where each PMU reports its own capabilities in the form of fixed/non-fixed counter limits. - In this PR/commit, it is *still* impossible to get more detailed (x86-only) counter information in terms of fixed/non-fixed counter association, 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 is bumped from 3 to 63, which together with the current padding "scheme" means we pre-allocate/inlline up-to 64 counter slots (64-bits each) per measurement instance - Closes #1377
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‎src/perf_counters.cc

+130-20
Original file line numberDiff line numberDiff line change
@@ -19,16 +19,133 @@
1919
#include <vector>
2020

2121
#if defined HAVE_LIBPFM
22+
#include <unordered_map>
2223
#include "perfmon/pfmlib.h"
2324
#include "perfmon/pfmlib_perf_event.h"
2425
#endif
2526

2627
namespace benchmark {
2728
namespace internal {
2829

29-
constexpr size_t PerfCounterValues::kMaxCounters;
30-
3130
#if defined HAVE_LIBPFM
31+
32+
class SinglePMURegistry {
33+
public:
34+
~SinglePMURegistry() = default;
35+
SinglePMURegistry(SinglePMURegistry&&) = default;
36+
SinglePMURegistry(const SinglePMURegistry&) = delete;
37+
SinglePMURegistry& operator=(SinglePMURegistry&&) noexcept;
38+
SinglePMURegistry& operator=(const SinglePMURegistry&) = delete;
39+
40+
SinglePMURegistry(pfm_pmu_t pmu_id)
41+
: pmu_id_(pmu_id), available_counters_(0), available_fixed_counters_(0) {
42+
{
43+
pfm_pmu_info_t pmu_info{};
44+
const auto pfm_pmu = pfm_get_pmu_info(pmu_id, &pmu_info);
45+
46+
if (pfm_pmu != PFM_SUCCESS) {
47+
GetErrorLogInstance() << "Unknown pmu: " << pmu_id << "\n";
48+
return;
49+
}
50+
51+
name_ = pmu_info.name;
52+
desc_ = pmu_info.desc;
53+
available_counters_ = pmu_info.num_cntrs;
54+
available_fixed_counters_ = pmu_info.num_fixed_cntrs;
55+
56+
BM_VLOG(1) << "PMU: " << pmu_id << " " << name_ << " " << desc_ << "\n";
57+
BM_VLOG(1) << " counters: " << available_counters_
58+
<< " fixed: " << available_fixed_counters_ << "\n";
59+
}
60+
}
61+
62+
const char* name() const { return name_; }
63+
64+
bool AddCounter(int event_id) {
65+
pfm_event_info_t info{};
66+
const auto pfm_event_info =
67+
pfm_get_event_info(event_id, PFM_OS_PERF_EVENT, &info);
68+
69+
if (pfm_event_info != PFM_SUCCESS) {
70+
GetErrorLogInstance() << "Unknown event id: " << event_id << "\n";
71+
return false;
72+
}
73+
74+
assert(info.pmu == pmu_id_);
75+
76+
if (counter_ids_.find(event_id) != counter_ids_.end()) return true;
77+
78+
assert(std::numeric_limits<int>::max() > counter_ids_.size());
79+
if (static_cast<int>(counter_ids_.size()) >= available_counters_ - 1) {
80+
GetErrorLogInstance() << "Maximal number of counters for PMU " << name_
81+
<< " (" << available_counters_ << ") reached.\n";
82+
return false;
83+
}
84+
85+
counter_ids_.emplace(event_id, info.code);
86+
87+
BM_VLOG(2) << "Registered counter: " << event_id << " (" << info.name
88+
<< " - " << info.desc << ") in pmu " << name_ << " ("
89+
<< counter_ids_.size() << "/" << available_counters_ << "\n";
90+
91+
return true;
92+
}
93+
94+
private:
95+
pfm_pmu_t pmu_id_;
96+
const char* name_;
97+
const char* desc_;
98+
std::unordered_map<int, uint64_t> counter_ids_;
99+
std::unordered_map<int, uint64_t> fixed_counter_ids_;
100+
int available_counters_;
101+
int available_fixed_counters_;
102+
};
103+
104+
class PMURegistry {
105+
public:
106+
~PMURegistry() = default;
107+
PMURegistry(PMURegistry&&) = default;
108+
PMURegistry(const PMURegistry&) = delete;
109+
PMURegistry& operator=(PMURegistry&&) noexcept;
110+
PMURegistry& operator=(const PMURegistry&) = delete;
111+
PMURegistry() {}
112+
113+
bool EnlistCounter(const std::string& name,
114+
struct perf_event_attr &attr_base) {
115+
attr_base.size = sizeof(attr_base);
116+
pfm_perf_encode_arg_t encoding{};
117+
encoding.attr = &attr_base;
118+
119+
const auto pfm_get = pfm_get_os_event_encoding(
120+
name.c_str(), PFM_PLM3, PFM_OS_PERF_EVENT, &encoding);
121+
if (pfm_get != PFM_SUCCESS) {
122+
GetErrorLogInstance() << "Unknown counter name: " << name << "\n";
123+
return false;
124+
}
125+
126+
pfm_event_info_t info{};
127+
const auto pfm_info =
128+
pfm_get_event_info(encoding.idx, PFM_OS_PERF_EVENT, &info);
129+
if (pfm_info != PFM_SUCCESS) {
130+
GetErrorLogInstance()
131+
<< "Unknown counter idx: " << encoding.idx << "(" << name << ")\n";
132+
return false;
133+
}
134+
135+
// Spin-up a new per-PMU sub-registry if needed
136+
if (pmu_registry_.find(info.pmu) == pmu_registry_.end()) {
137+
pmu_registry_.emplace(info.pmu, SinglePMURegistry(info.pmu));
138+
}
139+
140+
auto& single_pmu = pmu_registry_.find(info.pmu)->second;
141+
142+
return single_pmu.AddCounter(info.idx);
143+
}
144+
145+
private:
146+
std::unordered_map<pfm_pmu_t, SinglePMURegistry> pmu_registry_;
147+
};
148+
32149
const bool PerfCounters::kSupported = true;
33150

34151
bool PerfCounters::Initialize() { return pfm_initialize() == PFM_SUCCESS; }
@@ -38,35 +155,28 @@ PerfCounters PerfCounters::Create(
38155
if (counter_names.empty()) {
39156
return NoCounters();
40157
}
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-
}
158+
48159
std::vector<int> counter_ids(counter_names.size());
160+
PMURegistry registry{};
49161

50-
const int mode = PFM_PLM3; // user mode only
51162
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;
56163
const auto& name = counter_names[i];
57164
if (name.empty()) {
58165
GetErrorLogInstance() << "A counter name was the empty string\n";
59166
return NoCounters();
60167
}
61-
pfm_perf_encode_arg_t arg{};
62-
arg.attr = &attr;
63168

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";
169+
struct perf_event_attr attr {};
170+
auto ok = registry.EnlistCounter(name, attr);
171+
172+
if (!ok) {
173+
GetErrorLogInstance() << "Failed to register counter: " << name << "\n";
68174
return NoCounters();
69175
}
176+
177+
const bool is_first = i == 0;
178+
const int group_id = !is_first ? counter_ids[0] : -1;
179+
70180
attr.disabled = is_first;
71181
// Note: the man page for perf_event_create suggests inerit = true and
72182
// read_format = PERF_FORMAT_GROUP don't work together, but that's not the

‎src/perf_counters.h

+3-4
Original file line numberDiff line numberDiff line change
@@ -50,12 +50,11 @@ namespace internal {
5050
class PerfCounterValues {
5151
public:
5252
explicit PerfCounterValues(size_t nr_counters) : nr_counters_(nr_counters) {
53-
BM_CHECK_LE(nr_counters_, kMaxCounters);
53+
BM_CHECK_LE(nr_counters_, kMaxPreAllocatedCounters);
5454
}
55-
5655
uint64_t operator[](size_t pos) const { return values_[kPadding + pos]; }
5756

58-
static constexpr size_t kMaxCounters = 3;
57+
static constexpr size_t kMaxPreAllocatedCounters = 63;
5958

6059
private:
6160
friend class PerfCounters;
@@ -67,7 +66,7 @@ class PerfCounterValues {
6766
}
6867

6968
static constexpr size_t kPadding = 1;
70-
std::array<uint64_t, kPadding + kMaxCounters> values_;
69+
std::array<uint64_t, kPadding + kMaxPreAllocatedCounters> values_;
7170
const size_t nr_counters_;
7271
};
7372

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