linux-kernel - Re: [PATCH v3] NUMA: Early use of cpu_to_node() returns 0 instead of the correct node id

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Date: Mon, 8 Apr 2024 10:06:14 -0700 (PDT)
From: "Lameter, Christopher" <cl@...amperecomputing.com>
To: Andrew Morton <akpm@...ux-foundation.org>
cc: Huang Shijie <shijie@...amperecomputing.com>, gregkh@...uxfoundation.org, 
    patches@...erecomputing.com, rafael@...nel.org, paul.walmsley@...ive.com, 
    palmer@...belt.com, aou@...s.berkeley.edu, yury.norov@...il.com, 
    kuba@...nel.org, vschneid@...hat.com, mingo@...nel.org, vbabka@...e.cz, 
    rppt@...nel.org, tglx@...utronix.de, jpoimboe@...nel.org, 
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    arnd@...db.de, linux-kernel@...r.kernel.org, 
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    catalin.marinas@....com, will@...nel.org, mark.rutland@....com, 
    mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org, chenhuacai@...nel.org, 
    jiaxun.yang@...goat.com, linux-mips@...r.kernel.org
Subject: Re: [PATCH v3] NUMA: Early use of cpu_to_node() returns 0 instead
 of the correct node id

On Wed, 27 Mar 2024, Andrew Morton wrote:

>> In order to fix the bug, the patch introduces early_numa_node_init()
>> which is called after smp_prepare_boot_cpu() in start_kernel.
>> early_numa_node_init will initialize the "numa_node" as soon as
>> the early_cpu_to_node() is ready, before the cpu_to_node() is called
>> at the first time.
>
> What are the userspace-visible runtime effects of this bug?

Performance is reduced since there is increase in off node accesses.