Fixed spin count problem

Author: mrsharm

src/coreclr/gc/gc.cpp

@@ -91,6 +91,8 @@ BOOL bgc_heap_walk_for_etw_p = FALSE;
 
 #define UOH_ALLOCATION_RETRY_MAX_COUNT 2
 
+#define MAX_YP_SPIN_COUNT_UNIT 32768
+
 uint32_t yp_spin_count_unit = 0;
 uint32_t original_spin_count_unit = 0;
 size_t loh_size_threshold = LARGE_OBJECT_SIZE;
@@ -2288,6 +2290,7 @@ double      gc_heap::short_plugs_pad_ratio = 0;
 
 int         gc_heap::generation_skip_ratio_threshold = 0;
 int         gc_heap::conserve_mem_setting = 0;
+bool        gc_heap::spin_count_unit_config_p = false;
 
 uint64_t    gc_heap::suspended_start_time = 0;
 uint64_t    gc_heap::end_gc_time = 0;
@@ -13839,6 +13842,15 @@ HRESULT gc_heap::initialize_gc (size_t soh_segment_size,
     yp_spin_count_unit = 32 * g_num_processors;
 #endif //MULTIPLE_HEAPS
 
+    // Check if the values are valid for the spin count if provided by the user
+    // and if they are, set them as the yp_spin_count_unit and then ignore any updates made in SetYieldProcessorScalingFactor.
+    int64_t spin_count_unit_from_config = GCConfig::GetGCSpinCountUnit();
+    gc_heap::spin_count_unit_config_p = (spin_count_unit_from_config > 0) && (spin_count_unit_from_config <= MAX_YP_SPIN_COUNT_UNIT);
+    if (gc_heap::spin_count_unit_config_p)
+    {
+        yp_spin_count_unit = static_cast<int32_t>(spin_count_unit_from_config);
+    }
+
     original_spin_count_unit = yp_spin_count_unit;
 
 #if defined(__linux__)
@@ -45860,14 +45872,17 @@ size_t GCHeap::GetPromotedBytes(int heap_index)
 
 void GCHeap::SetYieldProcessorScalingFactor (float scalingFactor)
 {
-    assert (yp_spin_count_unit != 0);
-    uint32_t saved_yp_spin_count_unit = yp_spin_count_unit;
-    yp_spin_count_unit = (uint32_t)((float)original_spin_count_unit * scalingFactor / (float)9);
-
-    // It's very suspicious if it becomes 0 and also, we don't want to spin too much.
-    if ((yp_spin_count_unit == 0) || (yp_spin_count_unit > 32768))
+    if (!gc_heap::spin_count_unit_config_p)
     {
-        yp_spin_count_unit = saved_yp_spin_count_unit;
+        assert (yp_spin_count_unit != 0);
+        uint32_t saved_yp_spin_count_unit = yp_spin_count_unit;
+        yp_spin_count_unit = (uint32_t)((float)original_spin_count_unit * scalingFactor / (float)9);
+
+        // It's very suspicious if it becomes 0 and also, we don't want to spin too much.
+        if ((yp_spin_count_unit == 0) || (yp_spin_count_unit > MAX_YP_SPIN_COUNT_UNIT))
+        {
+            yp_spin_count_unit = saved_yp_spin_count_unit;
+        }
     }
 }
 

src/coreclr/gc/gcconfig.h

@@ -136,7 +136,8 @@ class GCConfigStringHolder
     INT_CONFIG   (GCEnabledInstructionSets,  "GCEnabledInstructionSets",  NULL,                                -1,                 "Specifies whether GC can use AVX2 or AVX512F - 0 for neither, 1 for AVX2, 3 for AVX512F")\
     INT_CONFIG   (GCConserveMem,             "GCConserveMemory",          "System.GC.ConserveMemory",          0,                  "Specifies how hard GC should try to conserve memory - values 0-9")                       \
     INT_CONFIG   (GCWriteBarrier,            "GCWriteBarrier",            NULL,                                0,                  "Specifies whether GC should use more precise but slower write barrier")                  \
-    STRING_CONFIG(GCName,                    "GCName",                    "System.GC.Name",                                        "Specifies the path of the standalone GC implementation.")                                
+    STRING_CONFIG(GCName,                    "GCName",                    "System.GC.Name",                                        "Specifies the path of the standalone GC implementation.")                                \
+    INT_CONFIG   (GCSpinCountUnit,           "GCSpinCountUnit",           0,                                   0,                  "Specifies the spin count unit used by the GC.")
 // This class is responsible for retreiving configuration information
 // for how the GC should operate.
 class GCConfig

src/coreclr/gc/gcpriv.h

@@ -4097,6 +4097,8 @@ class gc_heap
     PER_HEAP_ISOLATED_FIELD_INIT_ONLY int generation_skip_ratio_threshold;
     PER_HEAP_ISOLATED_FIELD_INIT_ONLY int conserve_mem_setting;
 
+    PER_HEAP_ISOLATED_FIELD_INIT_ONLY bool spin_count_unit_config_p;
+
     // For SOH we always allocate segments of the same
     // size unless no_gc_region requires larger ones.
     PER_HEAP_ISOLATED_FIELD_INIT_ONLY size_t soh_segment_size;