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use the CPU brand to determine the frequency

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=> reduce the boot time
This commit is contained in:
Stefan Lankes 2016-09-25 22:59:57 +02:00
parent 58059ed3e0
commit ebe41f1d46
1 changed files with 61 additions and 0 deletions
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61
hermit/arch/x86/kernel/processor.c
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@ -166,6 +166,63 @@ static void fpu_init_xsave(union fpu_state* fpu)
xs->fxsave.mxcsr = 0x1f80;
}
// Try to determine the frequency from the CPU brand.
// Code is derived from the manual "Intel Processor
// Identification and the CPUID Instruction".
static uint32_t get_frequency_from_brand(void)
{
char brand[4*3*sizeof(uint32_t)+1];
uint32_t eax = 0, ebx = 0;
uint32_t ecx = 0, edx = 0;
uint32_t index, multiplier = 0;
uint32_t* bint = (uint32_t*) brand;
memset(brand, 0x00, sizeof(brand));
cpuid(0x80000000, &eax, &ebx, &ecx, &edx);
if (eax >= 0x80000004)
{
cpuid(0x80000002, bint+0, bint+1, bint+2, bint+3);
cpuid(0x80000003, bint+4, bint+5, bint+6, bint+7);
cpuid(0x80000004, bint+8, bint+9, bint+10, bint+11);
kprintf("Processor: %s\n", brand);
for(index=0; index<sizeof(brand)-2; index++)
{
if ((brand[index+1] == 'H') && (brand[index+2] == 'z'))
{
if (brand[index] == 'M')
multiplier = 1;
else if (brand[index] == 'G')
multiplier = 1000;
else if (brand[index] == 'T')
multiplier = 1000000;
}
if (multiplier > 0) {
uint32_t freq;
// Compute frequency (in MHz) from brand string
if (brand[index-3] == '.') { // If format is “x.xx”
freq = (uint32_t)(brand[index-4] - '0') * multiplier;
freq += (uint32_t)(brand[index-2] - '0') * (multiplier / 10);
freq += (uint32_t)(brand[index-1] - '0') * (multiplier / 100);
} else { // If format is xxxx
freq = (uint32_t)(brand[index-4] - '0') * 1000;
freq += (uint32_t)(brand[index-3] - '0') * 100;
freq += (uint32_t)(brand[index-2] - '0') * 10;
freq += (uint32_t)(brand[index-1] - '0');
freq *= multiplier;
}
return freq;
}
}
}
return 0;
}
uint32_t detect_cpu_frequency(void)
{
uint64_t start, end, diff;
@ -174,6 +231,10 @@ uint32_t detect_cpu_frequency(void)
if (BUILTIN_EXPECT(cpu_freq > 0, 0))
return cpu_freq;
cpu_freq = get_frequency_from_brand();
if (cpu_freq > 0)
return cpu_freq;
old = get_clock_tick();
/* wait for the next time slice */