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False-sharing test #2

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False-sharing test #2

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3ef5800
Add logical thread ID arg to test function.
joshuascheid Apr 30, 2022
0890214
Add false-sharing add test.
joshuascheid Apr 30, 2022
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30 changes: 23 additions & 7 deletions bench.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ using namespace std::chrono;

using namespace Stats;

using cal_f = uint64_t(uint64_t iters);
using cal_f = uint64_t(size_t iters, size_t id);
using check_f = uint64_t();

#ifndef CHECK_RAC
Expand Down Expand Up @@ -132,7 +132,7 @@ uint64_t tls_counter::accumulator;
thread_local tls_counter tls_counter::tls;

HEDLEY_NEVER_INLINE
uint64_t tls_add(size_t iters) {
uint64_t tls_add(size_t iters, size_t id) {
while (iters--) {
tls_counter::increment();
}
Expand All @@ -141,7 +141,7 @@ uint64_t tls_add(size_t iters) {

static volatile uint64_t plain_counter;
// racy
uint64_t plain_add(size_t iters) {
uint64_t plain_add(size_t iters, size_t id) {
uint64_t rac_count = 0;
IF_RAC(uint64_t last = plain_counter - 1;)
while (iters--) {
Expand All @@ -151,6 +151,21 @@ uint64_t plain_add(size_t iters) {
return rac_count;
}

static constexpr size_t NUM_FS_COUNTERS = 64;
// Deterministic packed false-sharing.
alignas(64) static volatile uint8_t fs_counters[NUM_FS_COUNTERS];
uint64_t fs_add(size_t iters, size_t id) {
if (id >= NUM_FS_COUNTERS) {
error(EXIT_FAILURE, errno, "thread count exceeds structure %ld>=%ld",
id, NUM_FS_COUNTERS);
}
fs_counters[id] = 0;
while (iters--) {
fs_counters[id]++;
}
return fs_counters[id] != (iters & 0xff);
}

/**
* Simple counter which just uses a relaxed std::atomic increment.
*/
Expand Down Expand Up @@ -274,7 +289,7 @@ struct adaptor {
static T lock;
static uint64_t counter;

static uint64_t bench(size_t iters) {
static uint64_t bench(size_t iters, size_t id) {
uint64_t rac_count = 0;
IF_RAC(uint64_t last = counter - 1;)
while (iters--) {
Expand Down Expand Up @@ -304,20 +319,21 @@ test_func make_from_lock(const char *name, const char* desc = "desc") {

template <typename T, T* O>
test_func make_from_type(const char *name) {
return { [](size_t i) { return bench_template(*O, i); } , name , "desc" , []{ return O->read(); } };
return { [](size_t i, size_t id) { return bench_template(*O, i); } , name , "desc" , []{ return O->read(); } };
}

template <typename T>
test_func make_unchecked(const char *name) {
static T counter;
return { [](size_t i) {
return { [](size_t i, size_t id) {
return bench_template(counter, i);
}
, name , "desc" , nullptr };
}

std::vector<test_func> ALL_FUNCS = {
{plain_add , "plain add" , "desc" , nullptr } ,
{fs_add , "fs add" , "desc" , nullptr } ,
{tls_add , "tls add" , "desc" , tls_counter::read } ,
make_from_type<atomic_add_counter, &atomic_counter>("atomic add"),
make_from_type<atomic_cas_counter, &cas_counter>("cas add"),
Expand Down Expand Up @@ -572,7 +588,7 @@ struct test_thread {
uint64_t reacquires = 0;
auto t0 = CLOCK::now();
do {
reacquires += f(iters);
reacquires += f(iters, id);
result.total_iters += iters;
} while (now_nanos() < deadline);
auto t1 = CLOCK::now();
Expand Down