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

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Date: Fri, 19 Jan 2024 15:02:29 +0800
From: Shijie Huang <shijie@...eremail.onmicrosoft.com>
To: Yury Norov <yury.norov@...il.com>,
 Huang Shijie <shijie@...amperecomputing.com>
Cc: gregkh@...uxfoundation.org, patches@...erecomputing.com,
 rafael@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com,
 aou@...s.berkeley.edu, kuba@...nel.org, vschneid@...hat.com,
 mingo@...nel.org, akpm@...ux-foundation.org, vbabka@...e.cz,
 rppt@...nel.org, tglx@...utronix.de, jpoimboe@...nel.org,
 ndesaulniers@...gle.com, mikelley@...rosoft.com, mhiramat@...nel.org,
 arnd@...db.de, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 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,
 cl@...amperecomputing.com
Subject: Re: [PATCH] NUMA: Early use of cpu_to_node() returns 0 instead of the
 correct node id


在 2024/1/19 14:46, Shijie Huang 写道:
>
> 在 2024/1/19 12:42, Yury Norov 写道:
>> This adds another level of indirection, I think. Currently cpu_to_node
>> is a simple inliner. After the patch it would be a real function with
>> all the associate overhead. Can you share a bloat-o-meter output here?
> #./scripts/bloat-o-meter vmlinux vmlinux.new
> add/remove: 6/1 grow/shrink: 61/51 up/down: 1168/-588 (580)
> Function                                     old     new   delta
> numa_update_cpu                              148     244     +96
>
>  ...................................................................................................................................(to 
> many to skip)
>
> Total: Before=32990130, After=32990710, chg +0.00%
>
>
>>
>> Regardless, I don't think that the approach is correct. As per your
>> description, some initialization functions erroneously call
>> cpu_to_node() instead of early_cpu_to_node() which exists specifically
>> for that case.

sorry, I missed something.

I am not sure if  the early_cpu_to_node() works on all ARCHs.


Thanks

Huang Shijie

>>
>> If the above correct, it's clearly a caller problem, and the fix is to
>> simply switch all those callers to use early version.
>
> It is easy to change to early_cpu_to_node() for sched_init(), 
> init_sched_fair_class()
>
> and workqueue_init_early(). These three places call the cpu_to_node() 
> in the __init function.
>
>
> But it is a little hard to change the early_trace_init(), since it 
> calls cpu_to_node in the deep
>
> function stack:
>
>   early_trace_init() --> ring_buffer_alloc() -->rb_allocate_cpu_buffer()
>
>
> For early_trace_init(), we need to change more code.
>
>
> Anyway, If we think it is not a good idea to change the common code, I 
> am oaky too.
>
>
>>
>> I would also initialize the numa_node with NUMA_NO_NODE at declaration,
>> so that if someone calls cpu_to_node() before the variable is properly
>> initialized at runtime, he'll get NO_NODE, which is obviously an error.
>
> Even we set the numa_node with NUMA_NO_NODE, it does not always 
> produce error.
>
> Please see the alloc_pages_node().
>
>
> Thanks
>
> Huang Shijie
>