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

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Message-ID: <4BCEB276.6050909@redhat.com>
Date:	Wed, 21 Apr 2010 11:08:22 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Zachary Amsden <zamsden@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

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

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