tfscheduler: improve flp token selection bias

Author: ironMann

src/TfScheduler/TfSchedulerTokenManager.cxx

@@ -182,7 +182,6 @@ bool TfSchedulerTokenManager::connectTfBuilder(const std::string &pTfBuilderId,
 
 void TfSchedulerTokenManager::TokenManagerThread()
 {
-  static unsigned sRandomSeed = 0;
   std::uint64_t lSpinCounter = 0;
   std::uint64_t lNumReqSinceReset = 1000; // prevent throttling on init
 
@@ -229,7 +228,7 @@ void TfSchedulerTokenManager::TokenManagerThread()
 
     const bool lHaveReq = mTokenRequestQueue.consume_one([&](TokenRequestInfo &lReqInfo) {
         lReqInfo.mRequest.mTokensRequested &= mTokens;
-        lReplyTokenIdx = lReqInfo.mRequest.mTokensRequested.random_idx(sRandomSeed++);
+        lReplyTokenIdx = lReqInfo.mRequest.mTokensRequested.random_idx();
         assert ((lReplyTokenIdx == 0) || (lReplyTokenIdx && (lReqInfo.mRequest.mTokensRequested.get(lReplyTokenIdx) == true)));
         lReplyEp = lReqInfo.mReplyEp;
     });

src/common/base/Utilities.h

@@ -359,23 +359,26 @@ struct TokenBitfield {
     return sInvalidIdx;
   }
 
-  inline TokenBitfieldIndexType random_idx(TokenBitfieldIndexType seed) const {
-    seed = (seed ^ 0x4a981d8f) % NUM_TOKENS; // make sure index can wrap
+  inline TokenBitfieldIndexType random_idx() const {
 
-    for (TokenBitfieldIndexType i = 0; i < NUM_TOKENS; i++) {
-      if (mRequestTokenBitset[(seed % NUM_TOKENS) / NUM_ELEM_BITS] == 0) {
-        // jump to the next element
-        seed += NUM_ELEM_BITS;
-        continue;
-      }
+    TokenBitfieldIndexType idx = (rand() % NUM_TOKENS) + 1; // make sure index can wrap
+
+    int idxcnt = 0;
+    TokenBitfieldIndexType idxarr[4] = { 0 };
 
-      if (get(seed)) {
-        return (seed % NUM_TOKENS);
+    for (TokenBitfieldIndexType i = 0; i < NUM_TOKENS; i++, idx = (idx % NUM_TOKENS) + 1) {
+      assert (idx > 0);
+      assert (idx <= NUM_TOKENS);
+      if (get(idx)) {
+        idxarr[idxcnt++] = idx;
+
+        if (idxcnt == 4) {
+          break;
+        }
       }
-      seed++;
     }
 
-    return sInvalidIdx;
+    return (idxcnt == 0) ? sInvalidIdx : idxarr[rand() % idxcnt];
   }
 
   inline TokenBitfield& operator&=(const TokenBitfield& b) {

src/tests/test_Bitmap.cxx

@@ -48,22 +48,48 @@ BOOST_AUTO_TEST_CASE(GetNextSeqNameTest)
     TokenBitfield<256> lField1;
     TokenBitfield<256> lField2;
 
-    lField1.set(73);
     lField1.set(53);
+    lField1.set(73);
+    lField1.set(196);
+    lField1.set(197);
+    lField1.set(198);
+    lField1.set(199);
+    lField1.set(200);
+    lField1.set(201);
+    lField1.set(202);
 
     lField2.set(23);
     lField2.set(73);
+    lField2.set(196);
+    lField2.set(197);
+    lField2.set(198);
+    lField2.set(199);
+    lField2.set(200);
+    lField2.set(201);
+    lField2.set(202);
+
     lField2 &= lField1;
-    BOOST_CHECK(lField2.first() == 73);
-    BOOST_CHECK(lField2.random_idx(0) == 73);
-    BOOST_CHECK(lField2.random_idx(1) == 73);
-    BOOST_CHECK(lField2.random_idx(2) == 73);
-    BOOST_CHECK(lField2.random_idx(3) == 73);
-    BOOST_CHECK(lField2.random_idx(443) == 73);
-    BOOST_CHECK(lField2.random_idx(2222) == 73);
-
-    lField2.clr(73);
-    BOOST_CHECK(lField2.empty());
+
+    // lField2.set_all();
+
+    int hist[256] = { 0 };
+
+    BOOST_CHECK(lField2.get(73));
+
+
+
+    for (int i = 0; i < 100000; i ++) {
+      hist[lField2.random_idx() - 1] += 1;
+    }
+
+
+    for (int i = 0; i < 256; i ++) {
+      if (hist[i]) {
+        std::cout << "hist[" << i << "] = " << hist[i] << std::endl;
+      }
+    }
+
+    BOOST_CHECK(true);
   }