linux-kernel - Re: [PATCH] cpufreq: intel_pstate: Disable SMT when hybrid systems are enabled

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Message-ID: <20260122155549.GA18021@ranerica-svr.sc.intel.com>
Date: Thu, 22 Jan 2026 07:55:49 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Yaxiong Tian <tianyaxiong@...inos.cn>
Cc: srinivas.pandruvada@...ux.intel.com, lenb@...nel.org, rafael@...nel.org,
	viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cpufreq: intel_pstate: Disable SMT when hybrid systems
 are enabled

On Mon, Jan 19, 2026 at 03:41:18PM +0800, Yaxiong Tian wrote:
> When hwp_is_hybrid && !sched_smt_active(), the driver enables
> hybrid_capacity_scale and disables ITMT. According to the original code
> logic, these related actions are one-time operations; therefore, I
> believe the original design intent did not support dynamic runtime
> switching.
> 
> However, SMT can be toggled via related interfaces in /sys. When SMT is
> enabled, the system is no longer hybrid, and the original settings become
> incorrect.

Indeed I was able to enable SMT siblings:

	$ echo on > /sys/devices/system/cpu/smt
	$ echo 1 > /sys/devices/system/cpu/cpu1/online

> 
> To resolve this confusion, permanently disable SMT by calling
> cpuhp_smt_disable().

IMHO, the user should be able to enable SMT back if she or he chooses to. Instead,
the sched domains should be rebuilt with asym packing and without asymmetric
capacity.