Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S machine

[Dave Hansen]

On 10/9/22 18:23, Feng Tang wrote:
>>> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
>>> index cafacb2e58cc..b4ea79cb1d1a 100644
>>> --- a/arch/x86/kernel/tsc.c
>>> +++ b/arch/x86/kernel/tsc.c
>>> @@ -1217,7 +1217,7 @@ static void __init check_system_tsc_reliable(void)
>>>  	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
>>>  	    boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
>>>  	    boot_cpu_has(X86_FEATURE_TSC_ADJUST) &&
>>> -	    nr_online_nodes <= 2)
>>> +	    nr_online_nodes <= 8)
>> So you're saying all 8 socket systems since Broadwell (?) are TSC
>> sync'ed ?
> No, I didn't mean that. I haven't got chance to any 8 sockets
> machine, and I got a report last month that on one 8S machine,
> the TSC was judged 'unstable' by HPET as watchdog.

That's not a great check.  Think about numa=fake=4U, for instance.  Or a
single-socket system with persistent memory and high bandwidth memory.

Basically 'nr_online_nodes' is a software construct.  It's going to be
really hard to infer anything from it about what the _hardware_ is.