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boot: Use CPUID to detect TSC frequency

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Aside from being more accurate on CPUs that report the information this
is also orders of magnitude faster than sleeping for 1ms.
This commit is contained in:
Jan Janssen 2023-04-13 15:31:36 +02:00
parent 706fd67e4a
commit 2a3ae5fae0
1 changed files with 30 additions and 1 deletions
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31
src/boot/efi/ticks.c
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@ -5,6 +5,7 @@
#include "vmm.h"
#if defined(__i386__) || defined(__x86_64__)
# include <cpuid.h>
static uint64_t ticks_read_arch(void) {
/* The TSC might or might not be virtualized in VMs (and thus might not be accurate or start at zero
@ -17,7 +18,35 @@ static uint64_t ticks_read_arch(void) {
}
static uint64_t ticks_freq_arch(void) {
return 0;
/* Detect TSC frequency from CPUID information if available. */
unsigned max_leaf, ebx, ecx, edx;
if (__get_cpuid(0, &max_leaf, &ebx, &ecx, &edx) == 0)
return 0;
/* Leaf 0x15 is Intel only. */
if (max_leaf < 0x15 || ebx != signature_INTEL_ebx || ecx != signature_INTEL_ecx ||
edx != signature_INTEL_edx)
return 0;
unsigned denominator, numerator, crystal_hz;
__cpuid(0x15, denominator, numerator, crystal_hz, edx);
if (denominator == 0 || numerator == 0)
return 0;
uint64_t freq = crystal_hz;
if (crystal_hz == 0) {
/* If the crystal frquency is not available, try to deduce it from
* the processor frequency leaf if available. */
if (max_leaf < 0x16)
return 0;
unsigned core_mhz;
__cpuid(0x16, core_mhz, ebx, ecx, edx);
freq = core_mhz * 1000ULL * 1000ULL * denominator / numerator;
}
return freq * numerator / denominator;
}
#elif defined(__aarch64__)