linux-kernel - Re: [PATCH] Revert "intel_idle: Rescan "dead" SMT siblings during, initialization"

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Message-ID: <39dccf98-41da-4c54-a200-50f367cd0147@arm.com>
Date: Thu, 28 Aug 2025 22:44:41 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: linux-pm <linux-pm@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: Re: [PATCH] Revert "intel_idle: Rescan "dead" SMT siblings during,
 initialization"

On 8/28/25 20:06, Rafael J. Wysocki wrote:
> On Thu, Aug 28, 2025 at 6:13 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>
>> On Thu, Aug 28, 2025 at 4:44 PM Rafael J. Wysocki <rafael@...nel.org> wrote:
>>>
>>> On Thu, Aug 28, 2025 at 4:26 PM Christian Loehle
>>> <christian.loehle@....com> wrote:
>>>>
>>>> This reverts commit a430c11f401589a0f4f57fd398271a5d85142c7a.
>>>>
>>>> Calling arch_cpu_rescan_dead_smt_siblings() in intel_idle_init with
>>>> boot parameter nosmt and maxcpus active hotplugged boot-offline CPUs
>>>> in (and leave them online) which weren't supposed to be online.
>>>>
>>>> With the revert and nosmt and maxcpus=12 on a raptor lake:
>>>> cpu     online  capacity
>>>> cpu0    1       1009
>>>> cpu1    0       -
>>>> cpu2    1       1009
>>>> cpu3    0       -
>>>> cpu4    1       1009
>>>> cpu5    0       -
>>>> cpu6    1       1009
>>>> cpu7    0       -
>>>> cpu8    1       1024
>>>> cpu9    0       -
>>>> cpu10   1       1024
>>>> cpu11   0       -
>>>> cpu12   1       1009
>>>> cpu13   0       -
>>>> cpu14   1       1009
>>>> cpu15   0       -
>>>> cpu16   1       623
>>>> cpu17   1       623
>>>> cpu18   1       623
>>>> cpu19   1       623
>>>> cpu20   0       -
>>>> cpu21   0       -
>>>> cpu22   0       -
>>>> cpu23   0       -
>>>>
>>>> Previously:
>>>> cpu     online  capacity
>>>> cpu0    1       1009
>>>> cpu1    0       -
>>>> cpu2    1       1009
>>>> cpu3    0       -
>>>> cpu4    1       1009
>>>> cpu5    0       -
>>>> cpu6    1       1009
>>>> cpu7    0       -
>>>> cpu8    1       1024
>>>> cpu9    0       -
>>>> cpu10   1       1024
>>>> cpu11   0       -
>>>> cpu12   1       1009
>>>> cpu13   0       -
>>>> cpu14   1       1009
>>>> cpu15   0       -
>>>> cpu16   1       623
>>>> cpu17   1       623
>>>> cpu18   1       623
>>>> cpu19   1       623
>>>> cpu20   1       623
>>>> cpu21   1       623
>>>> cpu22   1       623
>>>> cpu23   1       623
>>>>
>>>> Signed-off-by: Christian Loehle <christian.loehle@....com>
>>>> ---
>>>> Rafael, I don't immediately see how to fix this properly so I won't
>>>> try to, feel free to treat this as a bug report.
>>>
>>> Sure, thanks for reporting this!
>>>
>>> Well, I think that cpuhp_smt_enable() is missing a check.  It looks to
>>> me like it should do the topology_is_primary_thread(cpu) check like
>>> cpuhp_smt_disable().
>>>
>>> I'll cut a test patch for this later.
>>
>> Something like the attached one, perhaps.  I haven't tested it yet,
>> but I'll do that later.
> 
> Works here AFAICS, but my test system is not hybrid.

Yep, on my end as well, thanks!
Tested-by: Christian Loehle <christian.loehle@....com>