From: Christian Loehle <christian.loehle@arm.com>
To: Thomas Gleixner <tglx@linutronix.de>,
"Rafael J. Wysocki" <rafael@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [PATCH] x86/topology: Implement topology_is_core_online() to address SMT regression
Date: Sun, 21 Sep 2025 12:00:11 +0100 [thread overview]
Message-ID: <d38b03ae-3958-42ae-867c-e08e7a4b3847@arm.com> (raw)
In-Reply-To: <87cy7k5gl3.ffs@tglx>
On 9/21/25 09:56, Thomas Gleixner wrote:
> Christian reported that commit a430c11f4015 ("intel_idle: Rescan "dead" SMT
> siblings during initialization") broke the use case in which both 'nosmt'
> and 'maxcpus' are on the kernel command line because it onlines primary
> threads, which were offline due to the maxcpus limit.
>
> The initially proposed fix to skip primary threads in the loop is
> inconsistent. While it prevents the primary thread to be onlined, it then
> onlines the corresponding hyperthread(s), which does not really make sense.
>
> The CPU iterator in cpuhp_smt_enable() contains a check which excludes all
> threads of a core, when the primary thread is offline. The default
> implementation is a NOOP and therefore not effective on x86.
>
> Implement topology_is_core_online() on x86 to address this issue. This
> makes the behaviour consistent between x86 and PowerPC.
>
> Fixes: a430c11f4015 ("intel_idle: Rescan "dead" SMT siblings during initialization")
> Fixes: f694481b1d31 ("ACPI: processor: Rescan "dead" SMT siblings during initialization")
> Reported-by: Christian Loehle <christian.loehle@arm.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Christian Loehle <christian.loehle@arm.com>
next prev parent reply other threads:[~2025-09-21 11:00 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-29 20:01 [PATCH v1] cpu: Add missing check to cpuhp_smt_enable() Rafael J. Wysocki
2025-09-02 15:05 ` Rafael J. Wysocki
2025-09-02 16:56 ` Dave Hansen
2025-09-02 17:18 ` Rafael J. Wysocki
2025-09-03 18:00 ` Dave Hansen
2025-09-03 18:35 ` Rafael J. Wysocki
2025-09-05 7:39 ` Thomas Gleixner
2025-09-05 13:13 ` Rafael J. Wysocki
2025-09-05 13:27 ` Rafael J. Wysocki
2025-09-05 20:47 ` Thomas Gleixner
2025-09-05 20:56 ` Rafael J. Wysocki
2025-09-07 13:14 ` Thomas Gleixner
2025-09-11 10:31 ` Rafael J. Wysocki
2025-09-21 8:56 ` [PATCH] x86/topology: Implement topology_is_core_online() to address SMT regression Thomas Gleixner
2025-09-21 11:00 ` Christian Loehle [this message]
2025-09-22 15:42 ` Rafael J. Wysocki
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