Re: [PATCH v4 7/7] thermal: intel: hfi: Notify user space for HFI events

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

On Wed, 2022-01-12 at 20:53 +0100, Rafael J. Wysocki wrote:
> On Sat, Jan 8, 2022 at 4:46 AM Ricardo Neri
> <ricardo.neri-calderon@linux.intel.com> wrote:
> > From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> > 
> > When the hardware issues an HFI event, relay a notification to user
> > space.
> > This allows user space to respond by reading performance and
> > efficiency of
> > each CPU and take appropriate action.
> > 
> > For example, when performance and efficiency of a CPU is 0, user
> > space can
> > either offline the CPU or inject idle. Also, if user space notices
> > a
> > downward trend in performance, it may proactively adjust power
> > limits to
> > avoid future situations in which performance drops to 0.
> > 
> > To avoid excessive notifications, the rate is limited by one HZ per
> > event.
> > To limit the netlink message size, parameters for only 16 CPUs at
> > max are
> > sent in one message. If there are more than 16 CPUs, issue as many
> > messages
> > as needed to notify the status of all CPUs.
> > 
> > In the HFI specification, both performance and efficiency
> > capabilities are
> > set in the [0, 255] range. The existing implementations of HFI
> > hardware
> > do not scale the maximum values to 255. Since userspace cares about
> > capability values that are either 0 or show a downward/upward
> > trend, this
> > fact does not matter much. Relative changes in capabilities are
> > enough. To
> > comply with the thermal netlink ABI, scale both performance and
> > efficiency
> > capabilities to the [0, 1023] interval.
> > 
> > Cc: Andi Kleen <ak@linux.intel.com>
> > Cc: Aubrey Li <aubrey.li@linux.intel.com>
> > Cc: Lukasz Luba <lukasz.luba@arm.com>
> > Cc: Tim Chen <tim.c.chen@linux.intel.com>
> > Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
> > Reviewed-by: Len Brown <len.brown@intel.com>
> > Signed-off-by: Srinivas Pandruvada <
> > srinivas.pandruvada@linux.intel.com>
> > ---
> > Changes since v3:
> >   * None
> > 
> > Changes since v2:
> >   * None
> > 
> > Changes since v1:
> >   * Made get_one_hfi_cap() return void. Removed unnecessary checks.
> >     (Rafael)
> >   * Replaced raw_spin_[un]lock_irq[restore|save]() with raw_spin_
> >     [un]lock_irq() in get_one_hfi_cap(). This function is only
> > called from
> >     a workqueue and there is no need to save and restore irq flags.
> >   * Scaled performance and energy efficiency values to a [0, 1023]
> > interval
> >     when reporting values to user space via thermal netlink
> > notifications.
> >     (Lucasz).
> >   * Reworded commit message to comment on the scaling of HFI
> > capabilities
> >     to comply with the proposed thermal netlink ABI.
> > ---
> >  drivers/thermal/intel/Kconfig     |  1 +
> >  drivers/thermal/intel/intel_hfi.c | 57
> > ++++++++++++++++++++++++++++++-
> >  2 files changed, 57 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/thermal/intel/Kconfig
> > b/drivers/thermal/intel/Kconfig
> > index e9d2925227d4..6cf3fe36a4ae 100644
> > --- a/drivers/thermal/intel/Kconfig
> > +++ b/drivers/thermal/intel/Kconfig
> > @@ -104,6 +104,7 @@ config INTEL_HFI_THERMAL
> >         bool "Intel Hardware Feedback Interface"
> >         depends on CPU_SUP_INTEL
> >         depends on X86_THERMAL_VECTOR
> > +       select THERMAL_NETLINK
> >         help
> >           Select this option to enable the Hardware Feedback
> > Interface. If
> >           selected, hardware provides guidance to the operating
> > system on
> > diff --git a/drivers/thermal/intel/intel_hfi.c
> > b/drivers/thermal/intel/intel_hfi.c
> > index 1a08c58f26f6..9fd66f176948 100644
> > --- a/drivers/thermal/intel/intel_hfi.c
> > +++ b/drivers/thermal/intel/intel_hfi.c
> > @@ -40,6 +40,7 @@
> > 
> >  #include <asm/msr.h>
> > 
> > +#include "../thermal_core.h"
> >  #include "intel_hfi.h"
> > 
> >  #define THERM_STATUS_CLEAR_PKG_MASK (BIT(1) | BIT(3) | BIT(5) |
> > BIT(7) | \
> > @@ -162,6 +163,60 @@ static struct hfi_features hfi_features;
> >  static DEFINE_MUTEX(hfi_instance_lock);
> > 
> >  #define HFI_UPDATE_INTERVAL    HZ
> > +#define HFI_MAX_THERM_NOTIFY_COUNT     16
> > +
> > +static void get_one_hfi_cap(struct hfi_instance *hfi_instance, s16
> > index,
> > +                           struct hfi_cpu_data *hfi_caps)
> > +{
> > +       struct hfi_cpu_data *caps;
> > +
> > +       /* Find the capabilities of @cpu */
> > +       raw_spin_lock_irq(&hfi_instance->table_lock);
> > +       caps = hfi_instance->data + index *
> > hfi_features.cpu_stride;
> > +       memcpy(hfi_caps, caps, sizeof(*hfi_caps));
> > +       raw_spin_unlock_irq(&hfi_instance->table_lock);
> > +}
> > +
> > +/*
> > + * Call update_capabilities() when there are changes in the HFI
> > table.
> > + */
> > +static void update_capabilities(struct hfi_instance *hfi_instance)
> > +{
> > +       struct cpu_capability cpu_caps[HFI_MAX_THERM_NOTIFY_COUNT];
> > +       int i = 0, cpu;
> > +
> 
> Wouldn't it be better to hold hfi_instance_lock for the duration of
> this loop?
As you expressed concern with more CPUs per package in future + netlink
processing the interrupts will be disabled for longer time.

But this can be optimized to have
void get_one_hfi_cap(struct hfi_instance *hfi_instance, s16 index,
struct hfi_cpu_data *hfi_caps)
with something like
void get_hfi_caps(struct hfi_instance *hfi_instance, s16 *cpu_count,
struct hfi_cpu_data **hfi_caps)
and take one lock for all
HFI_MAX_THERM_NOTIFY_COUNT CPUs.

Then keep thermal_genl_cpu_capability_event outside.
This ends up in calling thermal_genl_send_event() which has a long call
chain to netlink_broadcast() to format and broadcast message.

Thanks,
Srinivas

> 
> Surely, CPU offline or online during it can be confusing.
> 
> > +       for_each_cpu(cpu, hfi_instance->cpus) {
> > +               struct hfi_cpu_data caps;
> > +               s16 index;
> > +
> > +               /*
> > +                * We know index is valid because this CPU is
> > present
> > +                * in this instance.
> > +                */
> > +               index = per_cpu(hfi_cpu_info, cpu).index;
> > +
> > +               get_one_hfi_cap(hfi_instance, index, &caps);
> > +
> > +               cpu_caps[i].cpu = cpu;
> > +
> > +               /*
> > +                * Scale performance and energy efficiency to
> > +                * the [0, 1023] interval that thermal netlink
> > uses.
> > +                */
> > +               cpu_caps[i].performance = caps.perf_cap << 2;
> > +               cpu_caps[i].efficiency = caps.ee_cap << 2;
> > +               ++i;
> > +
> > +               if (i >= HFI_MAX_THERM_NOTIFY_COUNT) {
> > +                       thermal_genl_cpu_capability_event(HFI_MAX_T
> > HERM_NOTIFY_COUNT,
> > +                                                         cpu_caps)
> > ;
> > +                       i = 0;
> > +               }
> > +       }
> > +
> > +       if (i)
> > +               thermal_genl_cpu_capability_event(i, cpu_caps);
> > +}
> > 
> >  static void hfi_update_work_fn(struct work_struct *work)
> >  {
> > @@ -172,7 +227,7 @@ static void hfi_update_work_fn(struct
> > work_struct *work)
> >         if (!hfi_instance)
> >                 return;
> > 
> > -       /* TODO: Consume update here. */
> > +       update_capabilities(hfi_instance);
> >  }
> > 
> >  void intel_hfi_process_event(__u64 pkg_therm_status_msr_val)
> > --
> > 2.17.1
> >