Messages in this thread | | | Subject | Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S machine | From | Zhang Rui <> | Date | Tue, 11 Oct 2022 21:33:26 +0800 |
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On Tue, 2022-10-11 at 09:52 +0200, Peter Zijlstra wrote: > 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.
topology_max_packages() or variable logical_packages can tell the maximum packages. But this check_system_tsc_reliable() is done in early boot phase where we have boot cpu only. And the cpu topology is not built up at this stage.
thanks, rui
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