Re: [PATCH 1/5] Add a global synchronization point for pvclock

Avi Kivity
2010-04-21T08:08:22Z

On 04/21/2010 03:05 AM, Zachary Amsden wrote:
> On 04/19/2010 11:39 PM, Avi Kivity wrote:
>> On 04/19/2010 09:35 PM, Zachary Amsden wrote:
>>>>>> Sockets and boards too? (IOW, how reliable is TSC_RELIABLE)?
>>>>> Not sure, IIRC we clear that when the TSC sync test fails, eg when we
>>>>> mark the tsc clocksource unusable.
>>>>
>>>> Worrying. By the time we detect this the guest may already have
>>>> gotten confused by clocks going backwards.
>>>
>>>
>>> Upstream, we are marking the TSC unstable preemptively when hardware
>>> which will eventually sync test is detected, so this should be fine.
>>
>> ENOPARSE?
>>
>
> Instead of detecting TSC warp, c1e_idle, power_saving_mwait_init,
> tsc_check_state, dmi_mark_tsc_unstable all do something similar to
> this to disable TSC before warp even occurs:
>
> static void c1e_idle(void)
> {
> if (need_resched())
> return;
>
> if (!c1e_detected) {
> u32 lo, hi;
>
> rdmsr(MSR_K8_INT_PENDING_MSG, lo, hi);
> if (lo & K8_INTP_C1E_ACTIVE_MASK) {
> c1e_detected = 1;
> if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
> mark_tsc_unstable("TSC halt in AMD C1E");
> printk(KERN_INFO "System has AMD C1E enabled\n");
> set_cpu_cap(&boot_cpu_data, X86_FEATURE_AMDC1E);
> }
> }
>
>

That works within a socket; but multiple socket machines need not feed
all sockets from the same crystal and reset line (esp. likely for
multiple board machines, but might even happen with single board
FSB-less processors).

--
error compiling committee.c: too many arguments to function