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This commit is contained in:
Alexey Rybalchenko 2020-05-17 14:42:38 +02:00
parent b56e32eb11
commit 2916a491b9
1 changed files with 91 additions and 86 deletions
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177
fairmq/tools/RateLimit.h
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@ -38,97 +38,102 @@ namespace tools
*/ */
class RateLimiter class RateLimiter
{ {
using clock = std::chrono::steady_clock; using clock = std::chrono::steady_clock;
public: public:
/** /**
* Constructs a rate limiter. * Constructs a rate limiter.
* *
* \param rate Work rate in Hz (calls to maybe_sleep per second). Values less than/equal * \param rate Work rate in Hz (calls to maybe_sleep per second). Values less than/equal
* to 0 set the rate to 1 GHz (which is impossible to achieve, even with a * to 0 set the rate to 1 GHz (which is impossible to achieve, even with a
* loop that only calls RateLimiter::maybe_sleep). * loop that only calls RateLimiter::maybe_sleep).
*/ */
explicit RateLimiter(float rate) explicit RateLimiter(float rate)
: tw_req(std::chrono::seconds(1)) : tw_req(std::chrono::seconds(1))
, start_time(clock::now()) , start_time(clock::now())
{ {
if (rate <= 0) { if (rate <= 0) {
tw_req = std::chrono::nanoseconds(1); tw_req = std::chrono::nanoseconds(1);
} else {
tw_req = std::chrono::duration_cast<clock::duration>(tw_req / rate);
}
skip_check_count = std::max(1, int(std::chrono::milliseconds(5) / tw_req));
count = skip_check_count;
//std::cerr << "skip_check_count: " << skip_check_count << '\n';
}
/**
* Call this function at the end of the iteration rate limited loop.
*
* This function might use `std::this_thread::sleep_for` to limit the iteration rate. If no sleeps
* are necessary, the function will back off checking for the time to further allow increased
* iteration rates (until the requested rate or 1s between rechecks is reached).
*/
void maybe_sleep()
{
using namespace std::chrono;
if (--count == 0) {
auto now = clock::now();
if (tw == clock::duration::zero()) {
tw = (now - start_time) / skip_check_count;
} else {
tw = (1 * tw + 3 * (now - start_time) / skip_check_count) / 4;
}
//std::ostringstream s; s << "tw = " << std::setw(10) << duration_cast<nanoseconds>(tw).count() << "ns, req = " << duration_cast<nanoseconds>(tw_req).count() << "ns, ";
if (tw > tw_req * 65 / 64) {
// the time between maybe_sleep calls is more than 1% too long
// fix it by reducing ts towards 0 and if ts = 0 doesn't suffice, increase
// skip_check_count
if (ts > clock::duration::zero()) {
ts = std::max(clock::duration::zero(),
ts - (tw - tw_req) * skip_check_count * 1 / 2);
//std::cerr << s.str() << "maybe_sleep: going too slow; sleep less: " << duration_cast<microseconds>(ts).count() << "µs\n";
} else { } else {
skip_check_count = tw_req = std::chrono::duration_cast<clock::duration>(tw_req / rate);
std::min(int(seconds(1) / tw_req), // recheck at least every second
(skip_check_count * 5 + 3) / 4);
//std::cerr << s.str() << "maybe_sleep: going too slow; work more: " << skip_check_count << "\n";
} }
} else if (tw < tw_req * 63 / 64) { skip_check_count = std::max(1, int(std::chrono::milliseconds(5) / tw_req));
// the time between maybe_sleep calls is more than 1% too short count = skip_check_count;
// fix it by reducing skip_check_count towards 1 and if skip_check_count = 1 // std::cerr << "skip_check_count: " << skip_check_count << '\n';
// doesn't suffice, increase ts
// The minimum work count is defined such that a typical sleep time is greater
// than 1ms.
// The user requested 1/tw_req work iterations per second. Divided by 1000, that's
// the count per ms.
const int min_skip_count = std::max(1, int(milliseconds(5) / tw_req));
if (skip_check_count > min_skip_count) {
assert(ts == clock::duration::zero());
skip_check_count = std::max(min_skip_count, skip_check_count * 3 / 4);
//std::cerr << s.str() << "maybe_sleep: going too fast; work less: " << skip_check_count << "\n";
} else {
ts += (tw_req - tw) * (skip_check_count * 7) / 8;
//std::cerr << s.str() << "maybe_sleep: going too fast; sleep more: " << duration_cast<microseconds>(ts).count() << "µs\n";
}
}
start_time = now;
count = skip_check_count;
if (ts > clock::duration::zero()) {
std::this_thread::sleep_for(ts);
}
} }
}
private: /**
clock::duration tw{}, //! deduced duration between maybe_sleep calls * Call this function at the end of the iteration rate limited loop.
ts{}, //! sleep duration *
tw_req; //! requested duration between maybe_sleep calls * This function might use `std::this_thread::sleep_for` to limit the iteration rate. If no
clock::time_point start_time; * sleeps are necessary, the function will back off checking for the time to further allow
int count = 1; * increased iteration rates (until the requested rate or 1s between rechecks is reached).
int skip_check_count = 1; */
void maybe_sleep()
{
using namespace std::chrono;
if (--count == 0) {
auto now = clock::now();
if (tw == clock::duration::zero()) {
tw = (now - start_time) / skip_check_count;
} else {
tw = (1 * tw + 3 * (now - start_time) / skip_check_count) / 4;
}
// std::ostringstream s; s << "tw = " << std::setw(10) <<
// duration_cast<nanoseconds>(tw).count() << "ns, req = " <<
// duration_cast<nanoseconds>(tw_req).count() << "ns, ";
if (tw > tw_req * 65 / 64) {
// the time between maybe_sleep calls is more than 1% too long
// fix it by reducing ts towards 0 and if ts = 0 doesn't suffice, increase
// skip_check_count
if (ts > clock::duration::zero()) {
ts = std::max(clock::duration::zero(), ts - (tw - tw_req) * skip_check_count * 1 / 2);
// std::cerr << s.str() << "maybe_sleep: going too slow; sleep less: " <<
// duration_cast<microseconds>(ts).count() << "µs\n";
} else {
skip_check_count =
std::min(int(seconds(1) / tw_req), // recheck at least every second
(skip_check_count * 5 + 3) / 4);
// std::cerr << s.str() << "maybe_sleep: going too slow; work more: " <<
// skip_check_count << "\n";
}
} else if (tw < tw_req * 63 / 64) {
// the time between maybe_sleep calls is more than 1% too short
// fix it by reducing skip_check_count towards 1 and if skip_check_count = 1
// doesn't suffice, increase ts
// The minimum work count is defined such that a typical sleep time is greater
// than 1ms.
// The user requested 1/tw_req work iterations per second. Divided by 1000, that's
// the count per ms.
const int min_skip_count = std::max(1, int(milliseconds(5) / tw_req));
if (skip_check_count > min_skip_count) {
assert(ts == clock::duration::zero());
skip_check_count = std::max(min_skip_count, skip_check_count * 3 / 4);
// std::cerr << s.str() << "maybe_sleep: going too fast; work less: " <<
// skip_check_count << "\n";
} else {
ts += (tw_req - tw) * (skip_check_count * 7) / 8;
// std::cerr << s.str() << "maybe_sleep: going too fast; sleep more: " <<
// duration_cast<microseconds>(ts).count() << "µs\n";
}
}
start_time = now;
count = skip_check_count;
if (ts > clock::duration::zero()) {
std::this_thread::sleep_for(ts);
}
}
}
private:
clock::duration tw{}, //! deduced duration between maybe_sleep calls
ts{}, //! sleep duration
tw_req; //! requested duration between maybe_sleep calls
clock::time_point start_time;
int count = 1;
int skip_check_count = 1;
}; };
} /* namespace tools */ } /* namespace tools */