Re: [PATCH] cpufreq: intel_pstate: Enable asym capacity only when cpu smt is not possible

[Yaxiong Tian]

在 2026/1/29 05:21, Rafael J. Wysocki 写道:
> On Wed, Jan 28, 2026 at 4:15 AM Yaxiong Tian <tianyaxiong@xxxxxxxxxx> wrote:
> > According to the description in the intel_pstate.rst documentation,
> > Capacity-Aware Scheduling and Energy-Aware Scheduling are only
> > supported on a hybrid processor without SMT. Previously, the system
> > used sched_smt_active() for judgment, which is not a strict condition
> > because users can switch it on or off via /sys at any time.
> >
> > This could lead to incorrect driver settings in certain scenarios.
> >   For example, on a CPU that supports SMT, a user can disable SMT
> > via the nosmt parameter to enable asym capacity, and then re-enable
> > SMT via /sys. In such cases, some settings in the driver would no
> > longer be correct.
> >
> > To address this issue, replace sched_smt_active() with cpu_smt_possible(),
> > and only enable asym capacity when cpu smt is not possible.
> >
> > Fixes: 929ebc93ccaa ("cpufreq: intel_pstate: Set asymmetric CPU capacity on hybrid systems")
> > Signed-off-by: Yaxiong Tian <tianyaxiong@xxxxxxxxxx>
> > ---
> >   drivers/cpufreq/intel_pstate.c | 15 +++++++--------
> >   1 file changed, 7 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> > index ec4abe374573..8105c41861a3 100644
> > --- a/drivers/cpufreq/intel_pstate.c
> > +++ b/drivers/cpufreq/intel_pstate.c
> > @@ -1142,8 +1142,11 @@ static void hybrid_refresh_cpu_capacity_scaling(void)
> >
> >   static void hybrid_init_cpu_capacity_scaling(bool refresh)
> >   {
> > -       /* Bail out if enabling capacity-aware scheduling is prohibited. */
> > -       if (no_cas)
> > +       /*
> > +        * Bail out if capacity-aware scheduling is prohibited, or if SMT is
> > +        * possible, as the capacity of SMT threads cannot be determined reliably.
> > +        */
> > +       if (no_cas || cpu_smt_possible())
> >                  return;
> >
> >          /*
> > @@ -1156,12 +1159,8 @@ static void hybrid_init_cpu_capacity_scaling(bool refresh)
> >                  return;
> >          }
> >
> > -       /*
> > -        * On hybrid systems, use asym capacity instead of ITMT, but because
> > -        * the capacity of SMT threads is not deterministic even approximately,
> > -        * do not do that when SMT is in use.
> > -        */
> > -       if (hwp_is_hybrid && !sched_smt_active() && arch_enable_hybrid_capacity_scale()) {
> Why don't you replace sched_smt_active() here with cpu_smt_possible()?
>
> There's no point calling arch_enable_hybrid_capacity_scale() if the
> latter is true.
Because I think cpu_smt_possible() becomes fixed after kernel startup. 
Placing this check earlier can also prevent calling 
arch_enable_hybrid_capacity_scale(). Additionally, when users switch the 
cpufreq driver via /sys/devices/system/cpu/intel_pstate/status, it's 
unnecessary to proceed with further checks.
> > +       /* On hybrid systems, use asym capacity instead of ITMT */
> > +       if (hwp_is_hybrid && arch_enable_hybrid_capacity_scale()) {
> >                  hybrid_refresh_cpu_capacity_scaling();
> >                  /*
> >                   * Disabling ITMT causes sched domains to be rebuilt to disable asym
> > --