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Date:   Fri, 4 Feb 2022 16:47:58 -0800
From:   Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        Len Brown <len.brown@intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Aubrey Li <aubrey.li@linux.intel.com>,
        Amit Kucheria <amitk@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Lukasz Luba <lukasz.luba@arm.com>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Ricardo Neri <ricardo.neri@intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 0/7] Thermal: Introduce the Hardware Feedback
 Interface for thermal and performance management
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On Thu, Feb 03, 2022 at 07:57:25PM +0100, Rafael J. Wysocki wrote:
> On Sun, Jan 30, 2022 at 4:23 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Thu, Jan 27, 2022 at 8:33 PM Ricardo Neri
> > <ricardo.neri-calderon@linux.intel.com> wrote:
> > >
> > > Hi,
> > >
> > > This is v5 of this patchset after having incorporated the feedback from
> > > reviewers. Please find v1, v2, v3, and v4 in [1], [2], [3], and [4],
> > > respectively.
> > >
> > > The Intel Hardware Feedback Interface (HFI) [5] provides information about
> > > the performance and energy efficiency of each CPU in the system. It uses a
> > > table that is shared between hardware and the operating system. The
> > > contents of the table may be updated as a result of changes in the
> > > operating conditions of the system (e.g., reaching a thermal limit) or the
> > > action of external factors (e.g., changes in the thermal design power).
> > >
> > > The information that HFI provides are specified as numeric, unit-less
> > > capabilities relative to other CPUs in the system. These capabilities have
> > > a range of [0-255] where higher numbers represent higher capabilities.
> > > Energy efficiency and performance are reported in separate capabilities.
> > > If either the performance or energy capabilities efficiency of a CPU are 0,
> > > the hardware recommends to not schedule any tasks on such CPU for
> > > performance, energy efficiency or thermal reasons, respectively.
> > >
> > > The kernel or user space may use the information from the HFI to modify
> > > task placement and/or adjust power limits. This patchset focuses on the
> > > user space. The thermal notification framework is extended to relay
> > > updates of CPU capacity. Thus, a userspace daemon can affinitize workloads
> > > to certain CPUs and/or offline CPUs whose capabilities are zero.
> > >
> > > The frequency of HFI updates is specific to each processor model. On some
> > > systems, there is just a single HFI update at boot. On other systems, there
> > > may be updates every tens of milliseconds. In order to not overwhelm
> > > userspace with too many updates, they are limited to one update every
> > > CONFIG_HZ jiffies.
> > >
> > > Thanks and BR,
> > > Ricardo
> > >
> > > [1]. https://lore.kernel.org/lkml/20211106013312.26698-1-ricardo.neri-calderon@linux.intel.com/
> > > [2]. https://lore.kernel.org/lkml/20211220151438.1196-1-ricardo.neri-calderon@linux.intel.com/
> > > [3]. https://lore.kernel.org/lkml/20220106025059.25847-8-ricardo.neri-calderon@linux.intel.com/
> > > [4]. https://lore.kernel.org/lkml/20220108034743.31277-1-ricardo.neri-calderon@linux.intel.com/
> > > [5]. https://www.intel.com/sdm
> > >
> > > Changes since v4:
> > >  ++ Unchanged patches: 1, 2.
> > >  * Reworded description hfi_instance::hdr and hfi_instance::data.
> > >    (Patch 3; Srinivas)
> > >  * Call intel_hfi_online() before enabling the thermal vector at the
> > >    local APIC is enabled. This makes sure that a CPU has an associated
> > >    HFI instance when an HFI event happens. Reworded the commit message to
> > >    reflect this change. (Patch 4; Srinivas)
> > >  * Set hfi_instances to NULL if we fail to allocate memory for
> > >    hfi_instance::cpus. (Patch 4; Srinivas)
> > >  * Delayed initialization of local variables until after the check for a
> > >    non-NULL hfi_instances in intel_hfi_online(). (Patch 4; Srinivas)
> > >  * Optimized the error path in init_hfi_init() to not needlessly
> > >    free the memory of cpumasks that have not been allocated. (Patch 4;
> > >    Srinivas)
> > >  * Removed pointless checks for X86_FEATURE_HFI in
> > >    intel_hfi_[on|off]line(). It is sufficient to check for a non-NULL
> > >    hfi_instances or a CPU's hfi_instance. (Patch 4)
> > >  * Added a dedicated (i.e., not system_wq) workqueue to process HFI updates.
> > >    Reworded commit message accordingly. (Patch 5; Rafael)
> > >  * Repurposed comment on possibly receiving an HFI event with a NULL
> > >    hfi_cpu_info::instance. Patch 4 fixed this potential issue. Instead,
> > >    add a debug statement. (Patch 5; Srinivas)
> > >  * Wrapped check for NULL hfi_cpu_info::instance in the unlikely macro.
> > >    (Patch 5; Srinivas)
> > >  * Renamed struct cpu_capability as struct thermal_genl_cpu_caps.
> > >    (Patch 6; Rafael)
> > >  * Removed automatic variable ret from
> > >    thermal_genl_event_cpu_capability_change() and instead always return
> > >    -EMSGSIZE on error. (Patch 6; Rafael)
> > >  * Reworked parsing of HFI capabilities into chunks of
> > >    HFI_MAX_THERM_NOTIFY_COUNT CPUs at a time to reduce the time
> > >    we spend with interrupts disabled. (Patch7; Srinivas)
> > >  * Protected hfi_instance::cpus when iterating over them. (Patch 7;
> > >    Rafael)
> >
> > All patches in the series look good to me now, so I will be queuing it
> > up for 5.18 unless there are any objections or concerns.
> 
> The series has been applied as 5.18 material, thanks!

Thank you very much Rafael for taking the patches. Thanks everyone for
your feedback. It did improve the patches.

BR,
Ricardo