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

["Rafael J. Wysocki" <rafael@kernel.org>]

On Thu, Aug 28, 2025 at 11:44 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 8/28/25 20:06, Rafael J. Wysocki wrote:
> > On Thu, Aug 28, 2025 at 6:13 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >>
> >> On Thu, Aug 28, 2025 at 4:44 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >>>
> >>> On Thu, Aug 28, 2025 at 4:26 PM Christian Loehle
> >>> <christian.loehle@arm.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@arm.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@arm.com>

Thanks for testing and let me submit a proper patch.