TSC Problems (warp between CPUs)

From: Alex
Date: Fri Dec 27 2013 - 21:32:32 EST

Hi There,

Firstly, apologies for the length of this post, however there is a bit of information I need to give so it is clear to everyone
what is happening, what I have tried, and what I am hoping to achieve.

I am having a problem with getting the TSC clocksource to work on my new system. I have been trying to work with my motherboard manufacturer (gigabyte)
to try and alert them to a possible BIOS bug but I am not getting anywhere with them (replies in broken english, problem not being understood
by their support etc).

CPU: Intel i7-4930K
Motherboard: Gigabyte GA-X79-UP4 with latest bios.

Some info on the problem (various outputs of shell commands):

alex@desktop:~$ uname -a
Linux desktop 3.12.5-custom #1 SMP PREEMPT Sat Dec 21 17:28:12 EST 2013 x86_64 x86_64 x86_64 GNU/Linux

alex@desktop:~$ dmesg | grep -i tsc
tsc: Fast TSC calibration using PIT
tsc: Detected 3400.159 MHz processor
TSC deadline timer enabled
TSC synchronization [CPU#0 -> CPU#1]:
Measured 6618476436 cycles TSC warp between CPUs, turning off TSC clock.
tsc: Marking TSC unstable due to check_tsc_sync_source failed

alex@desktop:~$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
hpet acpi_pm

alex@desktop:~$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource

alex@desktop:~$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 62
model name : Intel(R) Core(TM) i7-4930K CPU @ 3.40GHz
stepping : 4
microcode : 0x416
cpu MHz : 3400.159
cache size : 12288 KB
physical id : 0
siblings : 12
core id : 0
cpu cores : 6
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 13
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm arat epb xsaveopt pln pts dtherm tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms
bogomips : 6800.31
clflush size : 64
cache_alignment : 64
address sizes : 46 bits physical, 48 bits virtual
power management:

processor : 1

<and this continues for processor id's up to 11>


As you can see "nonstop_tsc" is supported.

What I have tried doing to address the issue:

* Tried disabling all power/energy saving functions in the CPU cores
* CPU Eist/freqency Scaling is disabled.
* Nothing is overclocked.
* No CPU turbo function enabled.

None of the above have helped. Some digging around on the net has led me back to the BIOS being the issue, in that it is using an MSR to write to the TSC and leaving it in an inconsistent state.

An interesting quote I found online, apparently from a linux kernel dev:

so the way the hardware works is that there is 1 "master" tsc in the CPU package, that gets started when the cpu package comes out of reset. all logical cpus keep an offset value from that, which starts at 0, and the "master + offset" value is what gets returned on rdtsc. if someone writes to the tsc (using an MSR), what actually happens is that the master tsc does not change, only the per logical cpu offset gets changed.

Linux does not write to the TSC since quite a while... which means the BIOS is doing that. It really should not.

What I am wanting to know, is whether there is any way I can work around what is likely to be a BIOS bug by having the kernel intentionally reset the TSC.

I saw a patch floating around on the net that does something like this (for tsc-sync.c):

+ wrmsrl(MSR_IA32_TSC, 0);
start = get_cycles();

Is there any safe patch to force the TSC to be reset/reinitialized that I can add to the kernel?

I have a number of applications that will benefit from TSC timing rather than HPET and would really like to try and get TSC to work.

Kind Regards,

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/