Re: [PATCH V4 2/2] cpufreq: cppc: Add support for frequency invariance
From: Viresh Kumar
Date: Wed Feb 24 2021 - 23:45:52 EST
On 22-02-21, 16:57, Rafael J. Wysocki wrote:
>
On Mon, Feb 22, 2021 at 12:20 PM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
Even though the driver is located in drivers/cpufreq/ CPPC is part of
>
ACPI and so a CC to linux-acpi is missing.
I just used get-maintainers, perhaps we should add an entry for this
in MAINTAINERS, will be orphan though..
>
> diff --git a/drivers/cpufreq/Kconfig.arm b/drivers/cpufreq/Kconfig.arm
>
> index e65e0a43be64..a3e2d6dfea70 100644
>
> --- a/drivers/cpufreq/Kconfig.arm
>
> +++ b/drivers/cpufreq/Kconfig.arm
>
> @@ -19,6 +19,15 @@ config ACPI_CPPC_CPUFREQ
>
>
>
> If in doubt, say N.
>
>
>
> +config ACPI_CPPC_CPUFREQ_FIE
>
> + bool "Frequency Invariance support for CPPC cpufreq driver"
>
> + depends on ACPI_CPPC_CPUFREQ
>
>
In theory, the CPPC cpufreq driver can be used on systems with
>
nontrivial arch_freq_scale_tick() in which case the latter should be
>
used I suppose.
>
>
Would that actually happen if this option is enabled?
IIUC, you are saying that if this driver runs on x86 then we want
arch_freq_scale_tick() from arch/x86/kernel/smpboot.c to run instead
of this ? Yes that will happen because x86 doesn't enable
CONFIG_GENERIC_ARCH_TOPOLOGY and so this code will never trigger.
For other cases, like ARM AMU counters, the arch specific
implementation takes precedence to this.
>
> +static void __init cppc_freq_invariance_init(void)
>
> +{
>
> + struct cppc_perf_fb_ctrs fb_ctrs = {0};
>
> + struct cppc_freq_invariance *cppc_fi;
>
> + struct sched_attr attr = {
>
> + .size = sizeof(struct sched_attr),
>
> + .sched_policy = SCHED_DEADLINE,
>
> + .sched_nice = 0,
>
> + .sched_priority = 0,
>
> + /*
>
> + * Fake (unused) bandwidth; workaround to "fix"
>
> + * priority inheritance.
>
> + */
>
> + .sched_runtime = 1000000,
>
> + .sched_deadline = 10000000,
>
> + .sched_period = 10000000,
>
> + };
>
> + int i, ret;
>
> +
>
> + if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
>
> + return;
>
> +
>
> + kworker_fie = kthread_create_worker(0, "cppc_fie");
>
> + if (IS_ERR(kworker_fie))
>
> + return;
>
> +
>
> + for_each_possible_cpu(i) {
>
> + cppc_fi = &per_cpu(cppc_freq_inv, i);
>
> +
>
> + /* A policy failed to initialize, abort */
>
> + if (unlikely(!cppc_fi->cpu_data))
>
> + return cppc_freq_invariance_exit();
>
> +
>
> + kthread_init_work(&cppc_fi->work, cppc_scale_freq_workfn);
>
> + init_irq_work(&cppc_fi->irq_work, cppc_irq_work);
>
>
What would be wrong with doing the above in
>
cppc_freq_invariance_policy_init()? It looks like a better place to
>
me.
Can move it there as well, I just kept policy specific stuff there as
ideally I wanted to do everything here.
>
> + ret = sched_setattr_nocheck(kworker_fie->task, &attr);
>
>
And this needs to be done only once if I'm not mistaken.
Yes, I failed to fix this when I went to a single kworker.
--
viresh