Messages in this thread | | | Date | Tue, 11 Oct 2022 09:52:19 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S machine |
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On Mon, Oct 10, 2022 at 07:23:10AM -0700, Dave Hansen wrote: > 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.
We have both c->phys_proc_id and c->logical_proc_id along with logical_packages.
I'm thinking you want something like max(c->phys_proc_id) <= 4. Because even if you only populate 4 sockets of an 8 socket server you're up a creek without no paddles.
But it all comes down to how much drugs the firmware teams have had :/ It is entirely possible to enumerate with phys_proc_id==42 on a 2 socket system.
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