More precise hashrate calculation

- Use only steady timestamp counters to guarantee correctness
- CPU backend: directly measure total hashrate using raw hash counters from each thread; update data more often on ARM CPUs because they're slower
- GPU backends: directly measure total hashrate too, but use interpolator with 4 second lag to fix variance from batches of hashes

Total hashrate is now measured directly (realtime for CPU, 4 seconds lag for GPU), so it might differ a bit from the sum of all thread hashrates because data points are taken at different moments in time.

Overhead is reduced a lot since it doesn't have to go through all threads to calculate max total hashrate on every timer tick (2 times a second).

src/backend/common/HashrateInterpolator.cpp

@@ -0,0 +1,65 @@
+/* XMRig
+ * Copyright 2010      Jeff Garzik <jgarzik@pobox.com>
+ * Copyright 2012-2014 pooler      <pooler@litecoinpool.org>
+ * Copyright 2014      Lucas Jones <https://github.com/lucasjones>
+ * Copyright 2014-2016 Wolf9466    <https://github.com/OhGodAPet>
+ * Copyright 2016      Jay D Dee   <jayddee246@gmail.com>
+ * Copyright 2017-2018 XMR-Stak    <https://github.com/fireice-uk>, <https://github.com/psychocrypt>
+ * Copyright 2018-2020 SChernykh   <https://github.com/SChernykh>
+ * Copyright 2016-2020 XMRig       <https://github.com/xmrig>, <support@xmrig.com>
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+#include "backend/common/HashrateInterpolator.h"
+
+
+uint64_t xmrig::HashrateInterpolator::interpolate(uint64_t timeStamp) const
+{
+    timeStamp -= LagMS;
+
+    std::lock_guard<std::mutex> l(m_lock);
+
+    const size_t N = m_data.size();
+
+    if (N < 2) {
+        return 0;
+    }
+
+    for (size_t i = 0; i < N - 1; ++i) {
+        const auto& a = m_data[i];
+        const auto& b = m_data[i + 1];
+
+        if (a.second <= timeStamp && timeStamp <= b.second) {
+            return a.first + static_cast<int64_t>(b.first - a.first) * (timeStamp - a.second) / (b.second - a.second);
+        }
+    }
+
+    return 0;
+}
+
+void xmrig::HashrateInterpolator::addDataPoint(uint64_t count, uint64_t timeStamp)
+{
+    std::lock_guard<std::mutex> l(m_lock);
+
+    // Clean up old data
+    if (!m_data.empty()) {
+        while (timeStamp - m_data.front().second > LagMS * 2) {
+            m_data.pop_front();
+        }
+    }
+
+    m_data.emplace_back(count, timeStamp);
+}