[NTOS:KE] Don't loop indefinitely trying to figure out the CPU frequency. CORE-14419
authorThomas Faber <thomas.faber@reactos.org>
Thu, 1 Mar 2018 09:36:27 +0000 (10:36 +0100)
committerThomas Faber <thomas.faber@reactos.org>
Thu, 1 Mar 2018 13:26:44 +0000 (14:26 +0100)
Previously, we would keep sampling the CPU frequency until two subsequent
samples differed by at most 1 MHz. This could take several seconds, and would
unnecessarily delay boot.
Instead, if sampling is too unreliable, just give up and calculate the average
frequency from 10 samples. This is no worse than picking the frequency that
just happened to be returned twice in a row.

The fact that this method of sampling fails could indicate that there's a
problem with our performance counter implementation or timer interrupt,
but that's a separate issue...

ntoskrnl/ke/i386/kiinit.c

index cba2c42..c17f4dd 100644 (file)
@@ -44,7 +44,7 @@ KiInitMachineDependent(VOID)
     PFX_SAVE_AREA FxSaveArea;
     ULONG MXCsrMask = 0xFFBF;
     CPU_INFO CpuInfo;
     PFX_SAVE_AREA FxSaveArea;
     ULONG MXCsrMask = 0xFFBF;
     CPU_INFO CpuInfo;
-    KI_SAMPLE_MAP Samples[4];
+    KI_SAMPLE_MAP Samples[10];
     PKI_SAMPLE_MAP CurrentSample = Samples;
     LARGE_IDENTITY_MAP IdentityMap;
 
     PKI_SAMPLE_MAP CurrentSample = Samples;
     LARGE_IDENTITY_MAP IdentityMap;
 
@@ -240,11 +240,17 @@ KiInitMachineDependent(VOID)
                     CurrentSample++;
                     Sample++;
 
                     CurrentSample++;
                     Sample++;
 
-                    if (Sample == sizeof(Samples) / sizeof(Samples[0]))
+                    if (Sample == RTL_NUMBER_OF(Samples))
                     {
                     {
-                        /* Restart */
-                        CurrentSample = Samples;
-                        Sample = 0;
+                        /* No luck. Average the samples and be done */
+                        ULONG TotalMHz = 0;
+                        while (Sample--)
+                        {
+                            TotalMHz += Samples[Sample].MHz;
+                        }
+                        CurrentSample[-1].MHz = TotalMHz / RTL_NUMBER_OF(Samples);
+                        DPRINT1("Sampling CPU frequency failed. Using average of %lu MHz\n", CurrentSample[-1].MHz);
+                        break;
                     }
                 }
 
                     }
                 }