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 14:46:16 +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,
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Subject: Re: [PATCH] NUMA: Early use of cpu_to_node() returns 0 instead of the
 correct node id


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.
>
> 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