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/Workers.cpp

@@ -29,6 +29,7 @@
 #include "backend/common/Workers.h"
 #include "backend/cpu/CpuWorker.h"
 #include "base/io/log/Log.h"
+#include "base/tools/Chrono.h"
 #include "base/tools/Object.h"
 
 
@@ -142,13 +143,20 @@ void xmrig::Workers<T>::tick(uint64_t)
         return;
     }
 
+    uint64_t totalHashCount = 0;
+
     for (Thread<T> *handle : m_workers) {
         if (handle->worker()) {
             uint64_t hashCount, timeStamp;
             handle->worker()->getHashrateData(hashCount, timeStamp);
-            d_ptr->hashrate->add(handle->id(), hashCount, timeStamp);
+            d_ptr->hashrate->add(handle->id() + 1, hashCount, timeStamp);
+            totalHashCount += handle->worker()->rawHashes();
         }
     }
+
+    if (totalHashCount > 0) {
+        d_ptr->hashrate->add(0, totalHashCount, Chrono::steadyMSecs());
+    }
 }