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Message-ID: <c3817e18-e2ae-4ac2-b2b1-f68cf10ff418@amperemail.onmicrosoft.com>
Date: Thu, 28 Mar 2024 10:09:02 +0800
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v3] NUMA: Early use of cpu_to_node() returns 0 instead of
 the correct node id
To: Andrew Morton <akpm@linux-foundation.org>,
 Huang Shijie <shijie@os.amperecomputing.com>
Cc: gregkh@linuxfoundation.org, patches@amperecomputing.com,
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References: <20240126064451.5465-1-shijie@os.amperecomputing.com>
 <20240327111740.f8d3802b0eae15bcb8727e04@linux-foundation.org>
From: Shijie Huang <shijie@amperemail.onmicrosoft.com>
In-Reply-To: <20240327111740.f8d3802b0eae15bcb8727e04@linux-foundation.org>
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在 2024/3/28 2:17, Andrew Morton 写道:
> On Fri, 26 Jan 2024 14:44:51 +0800 Huang Shijie <shijie@os.amperecomputing.com> wrote:
>
>> During the kernel booting, the generic cpu_to_node() is called too early in
>> arm64, powerpc and riscv when CONFIG_NUMA is enabled.
>>
>> There are at least four places in the common code where
>> the generic cpu_to_node() is called before it is initialized:
>> 	   1.) early_trace_init()         in kernel/trace/trace.c
>> 	   2.) sched_init()               in kernel/sched/core.c
>> 	   3.) init_sched_fair_class()    in kernel/sched/fair.c
>> 	   4.) workqueue_init_early()     in kernel/workqueue.c
>>
>> 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?
>
For this bug, I do not see too much performance impact in the userspace 
applications.

It just pollutes the CPU caches in NUMA.


Thanks

Huang Shijie