Date:   Thu, 23 Jan 2020 16:30:36 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Giovanni Gherdovich <ggherdovich@...e.cz>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>, Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Paul Turner <pjt@...gle.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Quentin Perret <qperret@...rret.net>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Doug Smythies <dsmythies@...us.net>,
        Ionela Voinescu <ionela.voinescu@....com>
Subject: Re: [PATCH v5 0/6] Add support for frequency invariance for (some) x86

On Wed, Jan 22, 2020 at 4:10 PM Giovanni Gherdovich <ggherdovich@...e.cz> wrote:
>
> v4 at https://lore.kernel.org/lkml/20191113124654.18122-1-ggherdovich@suse.cz/
>
> Changes wrt v4:
>
> - Removing conditional access in the function arch_scale_freq_capacity()
>   and initialize arch_freq_scale to 1024 to account for when freq
>   invariance isn't enabled (Ionela V.)
> - In case the max frequency can't be read in MSRs, do not enable frequency
>   invariance at all (Ionela V., Peter Z.).
> - Renames:
>     variables:
>       arch_cpu_freq  -> arch_freq_scale
>       arch_max_freq  -> arch_max_freq_ratio
>       ... and others
>     functions:
>       init_scale_freq  -> init_counter_refs
>       set_cpu_max_freq -> init_freq_invariance
>       {core,skx,knl...}_set_cpu_max_freq  -> {core,skx,knl...}_set_max_freq_ratio
>       ... and others
> - Use the same function for parsing SKX and GLM registers (Peter Z.)
> - Pass a parameter to the function parsing KNL registers (Peter Z.)
> - Fix a bug whereby refs to [am]perf were initialized only on cpu #0
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> Cover Letter from v4:
>
> v3 at https://lore.kernel.org/lkml/20191111180549.12166-1-ggherdovich@suse.cz/
>
> Changes wrt v3:
>
> - Add definition of function set_arch_max_freq if !CONFIG_SMP
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> Cover Letter from v3:
>
> v2 at https://lore.kernel.org/lkml/20191002122926.385-1-ggherdovich@suse.cz/
>
> Changes wrt v2:
>
> - Removing the tick_disable mechanism. Frequency scale-invariance isn't
>   just about helping schedutil choose better frequencies, but also
>   providing the scheduler load balancer with better metrics. All users of
>   PELT signals benefit from this feature. The tick_disable patch disabled
>   frequency invariant calculation when a specific driver is in use
>   (intel_pstate in active mode).
>
> - static_branch_enable(&arch_scale_freq_key) is now called earlier, right
>   after we learn that X86_FEATURE_APERFMPERF is available. Previously Peter
>   Z. commented "if we can't tell the max_freq we don't want to use the
>   invariant stuff.". I've decided to do it differently: if we can't tell
>   the max_freq, then it's because the CPU encodes max_freq in MSRs in a way
>   this patch doesn't understand, and we assume max_p is the max_freq which
>   seems like a safe bet. As a reminder, max_freq=max_p is encoded by
>   setting arch_max_freq=1024 as default value. I'm open to feedback.
>
> - Refactoring the switch case statement in set_cpu_max_freq() as Rafael
>   W. Now the first patch doesn't hint at what the following patch will
>   bring along.
>
> - Handling the case were turbo is disabled at runtime and a _PPC ACPI
>   notification is issued, as requested by Rafael W. This happens eg. when
>   some laptop model is disconnected from AC. (Patch #6)
>
> - Handling all Intel x86_64 micro-arches.
>
> - A note for Srinivas P., who expressed concern for Atoms: on Atom CPUs the
>   max_freq is set to the highest turbo level, as a power-efficiency
>   oriented measure. In this way the ratio curr_freq/max_freq tends to be
>   lower, PELT signals are consequently lower, and schedutil doesn't push
>   too hard on speed. (Patches #4 and #5).
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> Cover Letter from v2:
>
> v1 at https://lore.kernel.org/lkml/20190909024216.5942-1-ggherdovich@suse.cz/
>
> Changes wrt v1:
>
> - add x86-specific implementation of arch_scale_freq_invariant() using a
>   static key that checks for the availability of APERF and MPERF
> - refer to GOLDMONT_D instead of GOLDMONT_X, according to recent rename
> - set arch_cpu_freq to 1024 from x86_arch_scale_freq_tick_disable() to prevent
>   PELT from being fed stale data
>
> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
> Cover Letter from v1:
>
> This is a resend with of Peter Zijlstra's patch to support frequency
> scale-invariance on x86 from May 2018 [see 1]. I've added some modifications
> and included performance test results. If Peter doesn't mind, I'm slapping my
> name on it :)
>
> The changes from Peter's original implementation are:
>
> 1) normalizing against the 4-cores turbo level instead or 1-core turbo
> 2) removing the run-time search for when the above value isn't found in the
>    various Intel MSRs -- the base frequency value is taken in that case.
>
> The section "4. KNOWN LIMITATIONS" in the first patch commit message addresses
> the reason why this approach was dropped back in 2018, and explains that the
> performance gains outweight that issue.
>
> The second patch from Srinivas is taken verbatim from the May 2018 submission
> as it still applies.
>
> I apologies for the length of patch #1 commit message; I've made a table of
> contents with summaries of each section that should make easier to skim
> through the content.
>
> This submission incorporates the feedback and requests for additional tests
> received during the presentation made at OSPM 2019 in Pisa three months ago.
>
> [1] https://lore.kernel.org/lkml/20180516044911.28797-2-srinivas.pandruvada@linux.intel.com/
>
> Giovanni Gherdovich (6):
>   x86,sched: Add support for frequency invariance
>   x86,sched: Add support for frequency invariance on SKYLAKE_X
>   x86,sched: Add support for frequency invariance on XEON_PHI_KNL/KNM
>   x86,sched: Add support for frequency invariance on ATOM_GOLDMONT*
>   x86,sched: Add support for frequency invariance on ATOM
>   x86: intel_pstate: handle runtime turbo disablement/enablement in
>     freq. invariance
>
>  arch/x86/include/asm/topology.h |  25 ++++
>  arch/x86/kernel/smpboot.c       | 290 +++++++++++++++++++++++++++++++++++++++-
>  drivers/cpufreq/intel_pstate.c  |   1 +
>  kernel/sched/core.c             |   1 +
>  kernel/sched/sched.h            |   7 +
>  5 files changed, 323 insertions(+), 1 deletion(-)
>

All looks good to me, so

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

for the whole series (and I'm assuming that it will go it through the tip tree).

Thanks!

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