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From: Viresh Kumar <viresh.kumar@linaro.org>
To: Ionela Voinescu <ionela.voinescu@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Will Deacon <will@kernel.org>,
	Russell King - ARM Linux <linux@armlinux.org.uk>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/8] cpufreq: allow drivers to flag custom support for freq invariance
Date: Thu, 9 Jul 2020 14:39:12 +0530
Message-ID: <20200709090912.vapouiruidgypxzc@vireshk-i7> (raw)
In-Reply-To: <20200709085354.GA5623@arm.com>

On 09-07-20, 09:53, Ionela Voinescu wrote:
> On Monday 06 Jul 2020 at 14:14:47 (+0200), Dietmar Eggemann wrote:
> > Why can't we just move the arch_set_freq_scale() call from cpufreq
> > driver to cpufreq core w/o introducing a FIE related driver flag?
> > 
> > Current scenario for Frequency Invariance Engine (FIE) on arm/arm64.
> > 
> > +------------------------------+       +------------------------------+
> > |                              |       |                              |
> > | cpufreq core:                |       | arch: (arm, arm64)           |
> > 
> > |                              |       |                              |
> > | weak arch_set_freq_scale() {}|       |                              |
> > |                              |       |                              |
> > +------------------------------+       |                              |
> >                                        |                              |
> > +------------------------------+       |                              |
> > |                              |       |                              |
> > | cpufreq driver:              |       |                              |
> > |                            +-----------> arch_set_freq_scale()      |
> > |                              |       |   {                          |
> > +------------------------------+       |      if (use counters)       |
> >                                        |        return;               |
> > +------------------------------+       |      ...                     |
> > |                              |       |   }                          |
> > | task scheduler:              |       |                              |
> > |                            +-----------> arch_scale_freq_tick()*    |
> > |                              |       |   {                          |
> > 
> > |                              |       |      if (!use counters)      |
> > |                              |       |        return;               |
> > |                              |       |      ...                     |
> > |                              |       |   }                          |
> > +------------------------------+       +------------------------------+
> > 
> > * defined as topology_scale_freq_tick() in arm64
> > 
> > Only Arm/Arm64 defines arch_set_freq_scale() to get the 'legacy' CPUfreq
> > based FIE. This would still be the case when we move
> > arch_set_freq_scale() from individual cpufreq drivers to cpufreq core.
> > 
> > Arm64 is the only arch which has to runtime-choose between two different
> > FIEs. This is currently done by bailing out early in one of the FIE
> > functions based on 'use counters'.
> > 
> > X86 (and others) will continue to not define arch_set_freq_scale().
> > 
> > The issue with CONFIG_BL_SWITCHER (vexpress-spc-cpufreq.c) could be
> > solved arm/arm64 internally (arch_topology.c) by putting
> > arch_set_freq_scale() under a !CONFIG_BL_SWITCHER guard.
> > I doubt that there are any arm bL systems out there running it. At least
> > I'm not aware of any complaints due to missing FIE support in bl
> > switcher setups so far.

I agree to that.

> Thank you Dietmar, for your review.
> 
> I was trying to suggest the same in my other replies.

I am sorry, I must have overlooked that part in your replies,
otherwise I may agreed to it :)

> Rafael, Viresh, would you mind confirming whether you still consider
> having an 'opt in' flag is preferable here?

Well, we wanted an opt-in flag instead of an opt-out one. And no flag
is certainly better.

-- 
viresh

  reply index

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-01  9:07 [PATCH 0/8] cpufreq: improve frequency invariance support Ionela Voinescu
2020-07-01  9:07 ` [PATCH 1/8] cpufreq: allow drivers to flag custom support for freq invariance Ionela Voinescu
2020-07-01 10:46   ` Viresh Kumar
2020-07-01 13:33     ` Ionela Voinescu
2020-07-01 16:05       ` Rafael J. Wysocki
2020-07-01 18:06         ` Ionela Voinescu
2020-07-02  2:58         ` Viresh Kumar
2020-07-02 11:44           ` Ionela Voinescu
2020-07-06 12:14             ` Dietmar Eggemann
2020-07-09  8:53               ` Ionela Voinescu
2020-07-09  9:09                 ` Viresh Kumar [this message]
2020-07-01  9:07 ` [PATCH 2/8] cpufreq: move invariance setter calls in cpufreq core Ionela Voinescu
2020-07-01 10:46   ` Viresh Kumar
2020-07-01 15:27     ` Ionela Voinescu
2020-07-01 15:51       ` Rafael J. Wysocki
2020-07-02  3:01         ` Viresh Kumar
2020-07-02 11:45         ` Ionela Voinescu
2020-07-01  9:07 ` [PATCH 3/8] cpufreq,drivers: remove setting of frequency scale factor Ionela Voinescu
2020-07-01  9:07 ` [PATCH 4/8] cpufreq,vexpress-spc: fix Frequency Invariance (FI) for bL switching Ionela Voinescu
2020-07-01 10:46   ` Viresh Kumar
2020-07-01 14:07     ` Ionela Voinescu
2020-07-02  3:05       ` Viresh Kumar
2020-07-02 11:41         ` Ionela Voinescu
2020-07-02 11:46           ` Viresh Kumar
2020-07-01  9:07 ` [PATCH 5/8] cpufreq: report whether cpufreq supports Frequency Invariance (FI) Ionela Voinescu
2020-07-01 10:46   ` Viresh Kumar
2020-07-01  9:07 ` [PATCH 6/8] arch_topology,cpufreq,sched/core: constify arch_* cpumasks Ionela Voinescu
2020-07-01  9:07 ` [PATCH 7/8] arch_topology,arm64: define arch_scale_freq_invariant() Ionela Voinescu
2020-07-01  9:07 ` [PATCH 8/8] cpufreq: make schedutil the default for arm and arm64 Ionela Voinescu

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