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kernel/x86: Use rdtsc in the fallback arch_debug_snooze case.

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This allows us to avoid extra calculations and read barriers
in spin() from system_time(), and it should be easier to detect
as an "idle loop" if emulators want to do that.
This commit is contained in:
Augustin Cavalier
2025-08-30 11:28:19 -04:00
parent b0c4061d51
commit 13e97a61cc
1 changed files with 20 additions and 25 deletions
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src/system/kernel/arch/x86/arch_debug.cpp
+20 -25
View File
@@ -1358,17 +1358,13 @@ arch_debug_gdb_get_registers(char* buffer, size_t bufferSize)
}
static void (*sDebugSnooze)(bigtime_t) = NULL;
static void (*sDebugSnooze)(uint32) = NULL;
static uint64 sDebugSnoozeConversionFactor = 0;
static void
debug_snooze_mwaitx(bigtime_t duration)
debug_snooze_mwaitx(uint32 delay)
{
uint32 delay = (duration * sDebugSnoozeConversionFactor) / 1000;
if (delay == 0)
delay = 1;
// monitorx (r/eax = pointer, ecx = extensions, edx = hints)
asm volatile(".byte 0x0f, 0x01, 0xfa;"
:: "a" (sDebugSnooze), "c" (0), "d" (0));
@@ -1380,12 +1376,8 @@ debug_snooze_mwaitx(bigtime_t duration)
static void
debug_snooze_tpause(bigtime_t duration)
debug_snooze_tpause(uint32 delay)
{
uint32 delay = (duration * sDebugSnoozeConversionFactor) / 1000;
if (delay == 0)
delay = 1;
memory_read_barrier();
uint64 target = __rdtsc() + delay;
@@ -1399,30 +1391,33 @@ debug_snooze_tpause(bigtime_t duration)
void
arch_debug_snooze(bigtime_t duration)
{
uint32 delay = (duration * sDebugSnoozeConversionFactor) / 1000;
if (delay == 0)
delay = 1;
if (sDebugSnooze != NULL) {
sDebugSnooze(duration);
sDebugSnooze(delay);
return;
}
spin(duration);
memory_read_barrier();
uint64 target = __rdtsc() + delay;
while (__rdtsc() < target)
arch_cpu_pause();
}
status_t
arch_debug_init(kernel_args* args)
{
bool haveMWAITX = x86_check_feature(IA32_FEATURE_AMD_EXT_MWAITX, FEATURE_EXT_AMD_ECX),
haveTPAUSE = x86_check_feature(IA32_FEATURE_WAITPKG, FEATURE_7_ECX);
if (haveMWAITX || haveTPAUSE) {
// Store the TSC frequency in kHz.
sDebugSnoozeConversionFactor =
(uint64(1000) << 32) / args->arch_args.system_time_cv_factor;
if (haveMWAITX)
sDebugSnooze = debug_snooze_mwaitx;
else if (haveTPAUSE)
sDebugSnooze = debug_snooze_tpause;
}
// Store the TSC frequency in kHz.
sDebugSnoozeConversionFactor =
(uint64(1000) << 32) / args->arch_args.system_time_cv_factor;
if (x86_check_feature(IA32_FEATURE_AMD_EXT_MWAITX, FEATURE_EXT_AMD_ECX))
sDebugSnooze = debug_snooze_mwaitx;
if (x86_check_feature(IA32_FEATURE_WAITPKG, FEATURE_7_ECX))
sDebugSnooze = debug_snooze_tpause;
add_debugger_command("where", &stack_trace, "Same as \"sc\"");
add_debugger_command("bt", &stack_trace, "Same as \"sc\" (as in gdb)");