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From: Ionela Voinescu <ionela.voinescu@arm.com>
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: catalin.marinas@arm.com, will@kernel.org, mark.rutland@arm.com,
	maz@kernel.org, suzuki.poulose@arm.com, sudeep.holla@arm.com,
	valentin.schneider@arm.com, rjw@rjwysocki.net,
	peterz@infradead.org, mingo@redhat.com,
	vincent.guittot@linaro.org, viresh.kumar@linaro.org,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v3 6/7] arm64: use activity monitors for frequency invariance
Date: Thu, 13 Feb 2020 09:47:04 +0000	[thread overview]
Message-ID: <20200213094704.GA30335@arm.com> (raw)
In-Reply-To: <a63fd15f-f02d-6afe-6e1f-817b9eb452d1@arm.com>

Hi Lukasz,

[..]
> > +
> > +/* Obtain max frequency (in KHz) as reported by hardware */
> > +__weak unsigned int cpu_get_max_freq(unsigned int cpu)
> > +{
> > +	return 0;
> > +}
> > +
> > +#ifdef CONFIG_CPU_FREQ
> > +/* Replace max frequency getter with cpufreq based function */
> > +#define cpu_get_max_freq cpufreq_get_hw_max_freq
> > +#endif
> 
> Can we just use cpufreq_get_hw_max_freq()?
> We have cpufreq_get_hw_max_freq returning 0 in such case, so it should
> be OK.
> 

The reasoning for the implementation is the following:
 - For CONFIG_CPU_FREQ we use cpufreq_get_hw_max_freq (weak default or
   strong alternative)
 - For !CONFIG_CPU_FREQ cpufreq_get_hw_max_freq returns 0 - it signals
   that cpufreq cannot return the hardware max frequency. In this case
   cpu_get_max_freq is used (weak default or strong alternative
   implementation).

> Is there a possibility that some platform which has !CONFIG_CPU_FREQ
> would define its own cpu_get_max_freq() overwriting the weak function
> above?
> Based on the code which checks 'if (unlikely(!max_freq_hz))' it should,
> otherwise 'valid_cpus' is not set.
> 
> I would assume that we won't see such platform, interested
> in AMU freq invariance without CONFIG_CPU_FREQ.
> 
> We already have a lot of these defines or __weak functions, which is
> hard to follow.

There is no dependency between CONFIG_CPU_FREQ and frequency invariance.
Therefore, I did not see a reason to potentially bypass the use of AMU
for frequency invariance for !CONFIG_CPU_FREQ.

But I agree it makes the code harder to read so I can remove
cpu_get_max_freq and keep cpufreq_get_hw_max_freq only until there is a
provable need for this. 

Thank you for the review,
Ionela.

  reply	other threads:[~2020-02-13  9:47 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 18:45 [PATCH v3 0/7] arm64: ARMv8.4 Activity Monitors support Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 1/7] arm64: add support for the AMU extension v1 Ionela Voinescu
2020-02-12 11:30   ` Suzuki Kuruppassery Poulose
2020-02-12 14:54     ` Valentin Schneider
2020-02-12 16:10     ` Ionela Voinescu
2020-02-12 16:20       ` Suzuki Kuruppassery Poulose
2020-02-12 18:20         ` Ionela Voinescu
2020-02-12 19:24           ` Suzuki K Poulose
2020-02-12 20:19         ` Ionela Voinescu
2020-02-12 16:24       ` Vladimir Murzin
2020-02-12 18:27         ` Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 2/7] arm64: trap to EL1 accesses to AMU counters from EL0 Ionela Voinescu
2020-02-12 11:44   ` Suzuki Kuruppassery Poulose
2020-02-12 15:36   ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 3/7] arm64/kvm: disable access to AMU registers from kvm guests Ionela Voinescu
2020-02-12 15:36   ` Valentin Schneider
2020-02-12 16:33   ` Suzuki Kuruppassery Poulose
2020-02-11 18:45 ` [PATCH v3 4/7] Documentation: arm64: document support for the AMU extension Ionela Voinescu
2020-02-12 15:36   ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 5/7] cpufreq: add function to get the hardware max frequency Ionela Voinescu
2020-02-12  4:14   ` Viresh Kumar
2020-02-13 11:59   ` Valentin Schneider
2020-02-13 12:59     ` Ionela Voinescu
2020-02-13 15:22       ` Valentin Schneider
2020-02-11 18:45 ` [PATCH v3 6/7] arm64: use activity monitors for frequency invariance Ionela Voinescu
2020-02-12 18:59   ` Lukasz Luba
2020-02-13  9:47     ` Ionela Voinescu [this message]
2020-02-17 16:59   ` Valentin Schneider
2020-02-23 18:49     ` Ionela Voinescu
2020-02-11 18:45 ` [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate Ionela Voinescu
2020-02-12  9:30   ` Valentin Schneider
2020-02-12 10:32     ` Ionela Voinescu
2020-02-12 10:01   ` Lukasz Luba
2020-02-12 10:12     ` Marc Zyngier
2020-02-12 10:54       ` Ionela Voinescu
2020-02-12 10:55       ` Lukasz Luba
2020-02-12 11:10         ` Marc Zyngier
2020-02-12 11:43           ` Lukasz Luba
2020-02-12 11:12         ` Valentin Schneider
2020-02-14  0:35   ` Thomas Gleixner
2020-02-14 15:45     ` Ionela Voinescu
2020-02-14 15:57       ` Ionela Voinescu

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