linux-kernel - Re: [PATCH 3/9] cpu/SMT: Store the current/max number of threads

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Date:   Tue, 13 Jun 2023 20:53:56 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Laurent Dufour <ldufour@...ux.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org
Cc:     linux-arch@...r.kernel.org, x86@...nel.org,
        dave.hansen@...ux.intel.com, mingo@...hat.com, bp@...en8.de,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 3/9] cpu/SMT: Store the current/max number of threads

On Tue, Jun 13 2023 at 19:16, Laurent Dufour wrote:
> On 10/06/2023 23:26:18, Thomas Gleixner wrote:
>> On Thu, May 25 2023 at 01:56, Michael Ellerman wrote:
>>>  #ifdef CONFIG_HOTPLUG_SMT
>>>  enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
>>> +static unsigned int cpu_smt_max_threads __ro_after_init;
>>> +unsigned int cpu_smt_num_threads;
>> 
>> Why needs this to be global? cpu_smt_control is pointlessly global already.
>
> I agree that cpu_smt_*_threads should be static.
>
> Howwever, regarding cpu_smt_control, it is used in 2 places in the x86 code:
>  - arch/x86/power/hibernate.c in arch_resume_nosmt()
>  - arch/x86/kernel/cpu/bugs.c in spectre_v2_user_select_mitigation()

Bah. I must have fatfingered the grep then.

> An accessor function may be introduced to read that value in these 2
> functions, but I'm wondering if that's really the best option.
>
> Unless there is a real need to change this through this series, I think
> cpu_smt_control can remain global.

That's fine.

Thanks,

        tglx