linux-kernel - Re: [PATCH v2] x86/tsc: Extend watchdog check exemption to 4-Sockets platform

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Message-ID: <a4860054-0f16-6513-f121-501048431086@intel.com>
Date:   Thu, 13 Oct 2022 09:02:43 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Feng Tang <feng.tang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Cc:     rui.zhang@...el.com, tim.c.chen@...el.com,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Yu Liao <liaoyu15@...wei.com>
Subject: Re: [PATCH v2] x86/tsc: Extend watchdog check exemption to 4-Sockets
 platform

On 10/13/22 06:12, Feng Tang wrote:
> @@ -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 <= 4)
>  		tsc_disable_clocksource_watchdog();

I still don't think we should perpetuate this hack.

This just plain doesn't work in numa=off numa=fake=... or presumably in
cases where NUMA is disabled in the firmware and memory is interleaved
across all sockets.

It also presumably doesn't work on two-socket systems that have
Cluster-on-Die or Sub-NUMA-Clustering where a single socket is chopped
up into multiple nodes.