In rare case, the TSC is every unstable or can't sync with real time hardware clock. After setting "tsc=unstable" in command line, system should use delay_without_tsc to detect timer IRQ. Or system could panic as shown in below log:
[ 0.000000] Command line: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx reboot_panic=p,w tsc=unstable gpt loglevel=8 xxxxxxxxxxxxxx vga=current nomodeset console=ttyS0,115200n8 xxxxxxxxxxxxxx [ 0.048000] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1 [ 0.049000] ..MP-BIOS bug: 8254 timer not connected to IO-APIC [ 0.049000] ...trying to set up timer (IRQ0) through the 8259A ... [ 0.049000] ..... (found apic 0 pin 2) ... [ 0.052000] ....... failed. [ 0.052000] ...trying to set up timer as Virtual Wire IRQ... [ 0.052000] ..... failed. [ 0.052000] ...trying to set up timer as ExtINT IRQ... [ 0.052000] ..... failed :(. [ 0.052000] Kernel panic - not syncing: IO-APIC + timer doesn't work! Boot with apic=debug and send a report. Then try booting with the 'noapic' option. [ 0.052000] [ 0.052000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.15.0-ga804a55 #5 [ 0.052000] Hardware name: Intel Corporation Tiger Lake Client Platform/TigerLake U LPDDR4 UDIMM, BIOS TGLSFWR1.R00.1063.A00.1802071025 02/07/2018 [ 0.052000] Call Trace: [ 0.052000] dump_stack+0x68/0x9d Signed-off-by: Liu Changcheng <[email protected]> diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index cf5d53c..dcfc5b9 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -17,6 +17,7 @@ typedef unsigned long long cycles_t; extern unsigned int cpu_khz; extern unsigned int tsc_khz; +extern int tsc_unstable; extern void disable_TSC(void); diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c index 7c55387..0809ec6 100644 --- a/arch/x86/kernel/apic/io_apic.c +++ b/arch/x86/kernel/apic/io_apic.c @@ -1643,7 +1643,7 @@ static int __init timer_irq_works(void) local_save_flags(flags); local_irq_enable(); - if (boot_cpu_has(X86_FEATURE_TSC)) + if (boot_cpu_has(X86_FEATURE_TSC) && !tsc_unstable) delay_with_tsc(); else delay_without_tsc(); diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index fb43027..27b1bae 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -36,7 +36,8 @@ EXPORT_SYMBOL(tsc_khz); /* * TSC can be unstable due to cpufreq or due to unsynced TSCs */ -static int __read_mostly tsc_unstable; +int __read_mostly tsc_unstable; +EXPORT_SYMBOL(tsc_unstable); /* native_sched_clock() is called before tsc_init(), so we must start with the TSC soft disabled to prevent -- 2.7.4
