linux-kernel - Re: [PATCH v2 1/2] arm64/arch_timer: include <linux/percpu.h>

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Date: Mon, 6 May 2024 11:40:17 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Puranjay Mohan <puranjay@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Sumit Garg <sumit.garg@...aro.org>, Stephen Boyd <swboyd@...omium.org>,
 Douglas Anderson <dianders@...omium.org>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Mark Rutland <mark.rutland@....com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH v2 1/2] arm64/arch_timer: include <linux/percpu.h>



On 5/3/24 15:14, Puranjay Mohan wrote:
> Anshuman Khandual <anshuman.khandual@....com> writes:
> 
>> On 5/2/24 18:04, Puranjay Mohan wrote:
>>> arch_timer.h includes linux/smp.h to use DEFINE_PER_CPU() and it works
>>> because smp.h includes percpu.h. The next commit will remove percpu.h
>>> from smp.h and it will break this usage.
>>>
>>> Explicitly include percpu.h and remove smp.h
>>
>> But this particular change does not seem to be necessary for changing
>> raw_smp_processor_id() as current_thread_info()->cpu being done in the
>> later patch ? You might still leave header <asm/percpu.h> inclusion in
>> arch/arm64/include/asm/smp.h while dropping the per cpu cpu_number ?
> 
> commit 57c82954e77f ("arm64: make cpu number a percpu variable")
> created this percpu variable and included <asm/percpu.h> in <asm/smp.h>
> 
> Now we are removing the percpu variable cpu_number from smp.h, so there
> is no need to keep percpu.h in smp.h

Fair enough.

> 
> I feel users of DECLARE_PER_CPU_[...], etc. should include percpu.h and
> not smp.h as it makes reading the code more easier and can thwart build
> issues in the future, when headers are changed. 
Right, makes sense, hope there is no more such cases using smp.h to pull
in DECLARE_PER_CPU_[...]. A quick build on defconfig is successful after
this patch.