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

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Date:   Wed, 12 Oct 2022 16:44:05 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>
CC:     Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "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 Tue, Oct 11, 2022 at 03:01:15PM +0200, Peter Zijlstra wrote:
> On Tue, Oct 11, 2022 at 03:51:21PM +0800, Feng Tang wrote:
> > Th simple patch below is to have a dedicate CPU nodemask and set it in
> > early SRAT CPU parsing, still it has problem when sub-numa is enabled
> > in BIOS where there are more NUMA nodes in SRAT table. (also I'm
> > not sure the change to amdtopology.c is right)
> 
> No; none of this has anything to do with nodes. This is about sockets.

Exactly. All we try to do is to get a closer number to the socket
numbers (also stated in current code comments)

According to our discussion, we haven't found a way to get a very
accurate number of sockets, so I plan to (if no objection):

* Send a patch lifting the socket number check from 2 to 4, to fix
  the issue reported by Yu Liao.

* Send another RFC patch[1], which makes the socket number more
  accurate, as it solve the 2 problems mentioned by Dave:
  - fakenuma (numa=fake=4 etc)
  - system with CPU-DRAM nodes + HBM nodes + Persistent Memory nodes
  but it still can't cover the subnuma enabled case 

[1]. https://lore.kernel.org/lkml/Y0UgeUIJSFNR4mQB@feng-clx/

Thanks,
Feng