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Date: Mon, 10 Oct 2022 09:23:28 +0800 From: Feng Tang <feng.tang@...el.com> To: Peter Zijlstra <peterz@...radead.org> CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>, "H . Peter Anvin" <hpa@...or.com>, <x86@...nel.org>, <linux-kernel@...r.kernel.org>, <rui.zhang@...el.com>, <tim.c.chen@...el.com>, Xiongfeng Wang <wangxiongfeng2@...wei.com>, Yu Liao <liaoyu15@...wei.com> Subject: Re: [PATCH] x86/tsc: Extend the watchdog check exemption to 4S/8S machine On Sun, Oct 09, 2022 at 03:01:32PM +0200, Peter Zijlstra wrote: > On Sun, Oct 09, 2022 at 01:12:09PM +0800, Feng Tang wrote: > > There is report again that the tsc clocksource on a 4 sockets x86 > > Skylake server was wrongly judged as 'unstable' by 'jiffies' watchdog, > > and disabled [1]. Also we got silimar reports on 8 sockets platform > > from internal test. > > > > Commit b50db7095fe0 ("x86/tsc: Disable clocksource watchdog for TSC > > on qualified platorms") was introduce to deal with these false > > alarms of tsc unstable issues, covering qualified platforms for 2 > > sockets or smaller ones. > > > > Extend the exemption also to 4/8 sockets to fix the issue. > > > > Rui also proposed another way to disable 'jiffies' as clocksource > > watchdog [2], which can also solve this specific problem in an > > architecture independent way, with one limitation that some tsc false > > alarms are reported by other watchdogs like HPET in post-boot time, > > while 'jiffies' is mostly used in boot phase before hardware > > clocksources are initialized. > > > > [1]. https://lore.kernel.org/all/9d3bf570-3108-0336-9c52-9bee15767d29@huawei.com/ > > [2]. https://lore.kernel.org/all/bd5b97f89ab2887543fc262348d1c7cafcaae536.camel@intel.com/ > > > > Reported-by: Yu Liao <liaoyu15@...wei.com> > > Tested-by: Yu Liao <liaoyu15@...wei.com> > > Signed-off-by: Feng Tang <feng.tang@...el.com> > > --- > > arch/x86/kernel/tsc.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > 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. > AFAIK there is no architectural guarantee for >4 sockets to have a sane > TSC. If there is one, the above should be limited to architectures that > conform. Thanks for the note! Yes, we should be very cautious for 8 sockets machine. Will limit the max sockets to 4, which was also originally suggested by Thomas. Thanks, Feng
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