From: Laurent Dufour <ldufour@linux.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org, dave.hansen@linux.intel.com,
x86@kernel.org, mingo@redhat.com, bp@alien8.de,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 3/9] cpu/SMT: Store the current/max number of threads
Date: Wed, 14 Jun 2023 14:27:40 +0200 [thread overview]
Message-ID: <bf213e3c-e296-0709-511d-b5c0ee36d9ee@linux.ibm.com> (raw)
In-Reply-To: <87sfav5h2z.ffs@tglx>
On 13/06/2023 20:53:56, Thomas Gleixner wrote:
> 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.
I spoke too quickly, cpu_smt_num_threads is used in the powerpc code.
When a new CPU is added it used to decide whether a thread has to be
onlined or not, and there is no way to pass it as argument at this time.
In details, it is used in topology_smt_thread_allowed() called by
dlpar_online_cpu() (see patch "powerpc/pseries: Honour current SMT state
when DLPAR onlining CPUs" at the end of this series).
I think the best option is to keep it global.
>>
>> 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
next prev parent reply other threads:[~2023-06-14 12:29 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 15:56 [PATCH 1/9] cpu/SMT: Move SMT prototypes into cpu_smt.h Michael Ellerman
2023-05-24 15:56 ` [PATCH 2/9] cpu/SMT: Move smt/control simple exit cases earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 3/9] cpu/SMT: Store the current/max number of threads Michael Ellerman
2023-06-10 21:26 ` Thomas Gleixner
2023-06-10 22:08 ` Thomas Gleixner
2023-06-13 17:16 ` Laurent Dufour
2023-06-13 18:53 ` Thomas Gleixner
2023-06-14 12:27 ` Laurent Dufour [this message]
2023-05-24 15:56 ` [PATCH 4/9] cpu/SMT: Create topology_smt_threads_supported() Michael Ellerman
2023-06-10 22:15 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 5/9] cpu/SMT: Create topology_smt_thread_allowed() Michael Ellerman
2023-06-10 22:35 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs Michael Ellerman
2023-06-10 20:09 ` Thomas Gleixner
2023-06-10 20:13 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 7/9] powerpc/pseries: Initialise CPU hotplug callbacks earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 8/9] powerpc: Add HOTPLUG_SMT support Michael Ellerman
2023-06-01 13:27 ` Laurent Dufour
2023-06-01 16:19 ` Laurent Dufour
2023-06-10 21:10 ` Thomas Gleixner
2023-06-12 15:20 ` Laurent Dufour
2023-06-12 16:34 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 9/9] powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs Michael Ellerman
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