[reactos] 02/02: [NTOS:KE/x64] Calculate the CPU frequency on AMD64

[Stanislav Motylkov]

https://git.reactos.org/?p=reactos.git;a=commitdiff;h=e2a587c2efc18e76b80a3…

commit e2a587c2efc18e76b80a39db41452f3f5616ab97
Author:     Stanislav Motylkov <x86corez(a)gmail.com>
AuthorDate: Wed Jul 12 15:28:48 2023 +0300
Commit:     Stanislav Motylkov <x86corez(a)gmail.com>
CommitDate: Sat Jul 15 20:50:12 2023 +0300

    [NTOS:KE/x64] Calculate the CPU frequency on AMD64
    
    This should be performed early enough before CM initialization,
    but after the TSC has been initialized and calibrated by HAL.
    
    Based on existing i386 kiinit code. CORE-17971 CORE-14922
---
 ntoskrnl/ke/amd64/krnlinit.c | 86 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/ntoskrnl/ke/amd64/krnlinit.c b/ntoskrnl/ke/amd64/krnlinit.c
index a946d92801c..9391219c25b 100644
--- a/ntoskrnl/ke/amd64/krnlinit.c
+++ b/ntoskrnl/ke/amd64/krnlinit.c
@@ -30,6 +30,89 @@ KiInitializeKernel(IN PKPROCESS InitProcess,
                    IN PLOADER_PARAMETER_BLOCK LoaderBlock);
 
 
+CODE_SEG("INIT")
+VOID
+KiCalculateCpuFrequency(
+    IN PKPRCB Prcb)
+{
+    if (Prcb->FeatureBits & KF_RDTSC)
+    {
+        ULONG Sample = 0;
+        CPU_INFO CpuInfo;
+        KI_SAMPLE_MAP Samples[10];
+        PKI_SAMPLE_MAP CurrentSample = Samples;
+
+        /* Start sampling loop */
+        for (;;)
+        {
+            /* Do a dummy CPUID to start the sample */
+            KiCpuId(&CpuInfo, 0);
+
+            /* Fill out the starting data */
+            CurrentSample->PerfStart = KeQueryPerformanceCounter(NULL);
+            CurrentSample->TSCStart = __rdtsc();
+            CurrentSample->PerfFreq.QuadPart = -50000;
+
+            /* Sleep for this sample */
+            KeStallExecutionProcessor(CurrentSample->PerfFreq.QuadPart * -1 / 10);
+
+            /* Do another dummy CPUID */
+            KiCpuId(&CpuInfo, 0);
+
+            /* Fill out the ending data */
+            CurrentSample->PerfEnd =
+                KeQueryPerformanceCounter(&CurrentSample->PerfFreq);
+            CurrentSample->TSCEnd = __rdtsc();
+
+            /* Calculate the differences */
+            CurrentSample->PerfDelta = CurrentSample->PerfEnd.QuadPart -
+                                       CurrentSample->PerfStart.QuadPart;
+            CurrentSample->TSCDelta = CurrentSample->TSCEnd -
+                                      CurrentSample->TSCStart;
+
+            /* Compute CPU Speed */
+            CurrentSample->MHz = (ULONG)((CurrentSample->TSCDelta *
+                                          CurrentSample->
+                                          PerfFreq.QuadPart + 500000) /
+                                         (CurrentSample->PerfDelta *
+                                          1000000));
+
+            /* Check if this isn't the first sample */
+            if (Sample)
+            {
+                /* Check if we got a good precision within 1MHz */
+                if ((CurrentSample->MHz == CurrentSample[-1].MHz) ||
+                    (CurrentSample->MHz == CurrentSample[-1].MHz + 1) ||
+                    (CurrentSample->MHz == CurrentSample[-1].MHz - 1))
+                {
+                    /* We did, stop sampling */
+                    break;
+                }
+            }
+
+            /* Move on */
+            CurrentSample++;
+            Sample++;
+
+            if (Sample == RTL_NUMBER_OF(Samples))
+            {
+                /* 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;
+            }
+        }
+
+        /* Save the CPU Speed */
+        Prcb->MHz = CurrentSample[-1].MHz;
+    }
+}
+
 VOID
 NTAPI
 KiInitializeHandBuiltThread(
@@ -105,6 +188,9 @@ KiSystemStartupBootStack(VOID)
         }
     }
 
+    /* Calculate the CPU frequency */
+    KiCalculateCpuFrequency(Prcb);
+
     /* Raise to Dispatch */
     KfRaiseIrql(DISPATCH_LEVEL);