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

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Message-ID: <CAJZ5v0h=OG-wgcZBD8mZ51+kb7j3yeDZQt9XfO=fdasLRgQkEg@mail.gmail.com>
Date: Thu, 28 Aug 2025 18:13:26 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christian Loehle <christian.loehle@....com>
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 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.

View attachment "kernel-cpu-enable-smt.patch" of type "text/x-patch" (505 bytes)