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Re: [PATCH v7 3/6] Kconfig: Make cpu hotplug configurable
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>
- Date: Wed, 8 Apr 2026 12:21:04 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 08 Apr 2026 12:21:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHcwDy29LsBHsG5wEG6AuodBSMA4bXG/lkAgA4lgoA=
- Thread-topic: [PATCH v7 3/6] Kconfig: Make cpu hotplug configurable
On 3/30/26 15:19, Jan Beulich wrote:
> On 30.03.2026 13:59, Mykyta Poturai wrote:
>> For the purposes of certification, we want as little code as possible to
>> be unconditionally compiled in. Make CPU hotplug and SMT operations
>> configurable to ease the process. This will also help with introducing
>> CPU hotplug on Arm, where it needs to be configurable.
>>
>> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
>
> Looks largely okay from a technical pov; one nit and one (repeated) remark
> below.
>
>> --- a/xen/arch/x86/sysctl.c
>> +++ b/xen/arch/x86/sysctl.c
>> @@ -53,6 +53,11 @@ static long cf_check smt_up_down_helper(void *data)
>> unsigned int cpu, sibling_mask = boot_cpu_data.x86_num_siblings - 1;
>> int ret = 0;
>>
>> + if ( !IS_ENABLED(CONFIG_CPU_HOTPLUG) )
>> + {
>> + ASSERT_UNREACHABLE();
>> + return -EOPNOTSUPP;
>> + }
>> opt_smt = up;
>
> Another blank line above this one perhaps?
>
>> --- a/xen/common/Kconfig
>> +++ b/xen/common/Kconfig
>> @@ -637,6 +637,14 @@ config SYSTEM_SUSPEND
>>
>> If unsure, say N.
>>
>> +config CPU_HOTPLUG
>> + bool "CPU online/offline support"
>> + depends on X86
>> + default y
>> + help
>> + Enable support for bringing CPUs online and offline at runtime. On
>> + X86 this is required for disabling SMT.
>
> The name of this option may need input from others; I'm not quite convinced
> that this is a good name, as there's no true "hot-plugging" involved here.
> IOW I fear the present name is misleading.
>
> Jan
My first idea was "CONFIG_RUNTIME_CPU_CONTROL" I can switch back to it.
--
Mykyta
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