Hey,
On Friday 18 Jun 2021 at 13:07:13 (+0530), Viresh Kumar wrote:
> On 17-06-21, 11:34, Ionela Voinescu wrote:
> > We can't queue any more work for it as there's no tick for the offline
> > CPU.
>
> Okay, so as discussed yesterday and confirmed by Peter, CPU hotplug shouldn't be
> a problem and we can avoid handling that here. Good.
>
> The patch 1/3 from this series is not required anymore. I will get rid of
> stop_cpu() as well.
>
> The second patch stays as is, as I still don't see another way of fixing the
> same problem on policy ->exit(). We still need that guarantee from topology
> core.
>
Right! That is because we need to make sure the tick does not queue any
more irq work while we do our cleanup (irq_work_sync() and then
kthread_cancel_work_sync()). Then kthread_cancel_work_sync() would
ensure the last worker wraps up so we can free the data.
I was hoping to avoid this but I don't currently see another way either.
> > P.S. I'll give more thought to the rcu use in the arch_topology driver.
> > I'm the boring kind that likes to err on the side of caution, so I tend
> > to agree that it might be good to have even if the current problem could
> > be solved in this driver.
>
> Before I resend the series again, maybe it is better to align on the idea here
> itself first (as I need to fix some existing potential memleaks in policy
> ->init() first). So here is the new diff, looks okay now ?
>
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index be4f62e2c5f1..3e9070f107c5 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -10,14 +10,18 @@
>
> #define pr_fmt(fmt) "CPPC Cpufreq:" fmt
>
> +#include <linux/arch_topology.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
> #include <linux/delay.h>
> #include <linux/cpu.h>
> #include <linux/cpufreq.h>
> #include <linux/dmi.h>
> +#include <linux/irq_work.h>
> +#include <linux/kthread.h>
> #include <linux/time.h>
> #include <linux/vmalloc.h>
> +#include <uapi/linux/sched/types.h>
>
> #include <asm/unaligned.h>
>
> @@ -57,6 +61,214 @@ static struct cppc_workaround_oem_info wa_info[] = {
> }
> };
>
> +#ifdef CONFIG_ACPI_CPPC_CPUFREQ_FIE
> +
> +/* Frequency invariance support */
> +struct cppc_freq_invariance {
> + int cpu;
> + struct irq_work irq_work;
> + struct kthread_work work;
> + struct cppc_perf_fb_ctrs prev_perf_fb_ctrs;
> + struct cppc_cpudata *cpu_data;
> +};
> +
> +static DEFINE_PER_CPU(struct cppc_freq_invariance, cppc_freq_inv);
> +static struct kthread_worker *kworker_fie;
> +
> +static struct cpufreq_driver cppc_cpufreq_driver;
> +static unsigned int hisi_cppc_cpufreq_get_rate(unsigned int cpu);
> +static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t0,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t1);
> +
> +/**
> + * cppc_scale_freq_workfn - CPPC arch_freq_scale updater for frequency invariance
> + * @work: The work item.
> + *
> + * The CPPC driver register itself with the topology core to provide its own
> + * implementation (cppc_scale_freq_tick()) of topology_scale_freq_tick() which
> + * gets called by the scheduler on every tick.
> + *
> + * Note that the arch specific counters have higher priority than CPPC counters,
> + * if available, though the CPPC driver doesn't need to have any special
> + * handling for that.
> + *
> + * On an invocation of cppc_scale_freq_tick(), we schedule an irq work (since we
> + * reach here from hard-irq context), which then schedules a normal work item
> + * and cppc_scale_freq_workfn() updates the per_cpu arch_freq_scale variable
> + * based on the counter updates since the last tick.
> + */
> +static void cppc_scale_freq_workfn(struct kthread_work *work)
> +{
> + struct cppc_freq_invariance *cppc_fi;
> + struct cppc_perf_fb_ctrs fb_ctrs = {0};
> + struct cppc_cpudata *cpu_data;
> + unsigned long local_freq_scale;
> + u64 perf;
> +
> + cppc_fi = container_of(work, struct cppc_freq_invariance, work);
> + cpu_data = cppc_fi->cpu_data;
> +
> + if (cppc_get_perf_ctrs(cppc_fi->cpu, &fb_ctrs)) {
> + pr_warn("%s: failed to read perf counters\n", __func__);
> + return;
> + }
> +
> + perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
> + &fb_ctrs);
> + cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
> +
> + perf <<= SCHED_CAPACITY_SHIFT;
> + local_freq_scale = div64_u64(perf, cpu_data->perf_caps.highest_perf);
> +
> + /* This can happen due to counter overflows */
> + if (unlikely(local_freq_scale > 1024))
> + local_freq_scale = 1024;
> +
> + per_cpu(arch_freq_scale, cppc_fi->cpu) = local_freq_scale;
> +}
> +
> +static void cppc_irq_work(struct irq_work *irq_work)
> +{
> + struct cppc_freq_invariance *cppc_fi;
> +
> + cppc_fi = container_of(irq_work, struct cppc_freq_invariance, irq_work);
> + kthread_queue_work(kworker_fie, &cppc_fi->work);
> +}
> +
> +static void cppc_scale_freq_tick(void)
> +{
> + struct cppc_freq_invariance *cppc_fi = &per_cpu(cppc_freq_inv, smp_processor_id());
> +
> + /*
> + * cppc_get_perf_ctrs() can potentially sleep, call that from the right
> + * context.
> + */
> + irq_work_queue(&cppc_fi->irq_work);
> +}
> +
> +static struct scale_freq_data cppc_sftd = {
> + .source = SCALE_FREQ_SOURCE_CPPC,
> + .set_freq_scale = cppc_scale_freq_tick,
> +};
> +
> +static int cppc_cpufreq_cpu_fie_init(struct cpufreq_policy *policy)
> +{
> + struct cppc_freq_invariance *cppc_fi;
> + int cpu, ret;
> +
> + if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> + return 0;
> +
> + for_each_cpu(cpu, policy->cpus) {
> + cppc_fi = &per_cpu(cppc_freq_inv, cpu);
> + cppc_fi->cpu = cpu;
> + cppc_fi->cpu_data = policy->driver_data;
> + kthread_init_work(&cppc_fi->work, cppc_scale_freq_workfn);
> + init_irq_work(&cppc_fi->irq_work, cppc_irq_work);
> +
> + ret = cppc_get_perf_ctrs(cpu, &cppc_fi->prev_perf_fb_ctrs);
> + if (ret) {
> + pr_warn("%s: failed to read perf counters for cpu:%d: %d\n",
> + __func__, cpu, ret);
> +
> + /* Avoid failing driver's probe because of FIE */
> + return 0;
> + }
> + }
> +
> + /* Register for freq-invariance */
> + topology_set_scale_freq_source(&cppc_sftd, policy->cpus);
> + return 0;
> +}
> +
> +/*
> + * We free all the resources on policy's removal and not on CPU removal as the
> + * irq-work are per-cpu and the hotplug core takes care of flushing the pending
> + * irq-works (hint: smpcfd_dying_cpu()) on CPU hotplug. Even if the kthread-work
> + * fires on another CPU after the concerned CPU is removed, it won't harm.
> + *
> + * We just need to make sure to remove them all on policy->exit().
> + */
> +static void cppc_cpufreq_cpu_fie_exit(struct cpufreq_policy *policy)
> +{
> + struct cppc_freq_invariance *cppc_fi;
> + int cpu;
> +
> + if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> + return;
> +
> + /* policy->cpus will be empty here, use related_cpus instead */
> + topology_clear_scale_freq_source(SCALE_FREQ_SOURCE_CPPC, policy->related_cpus);
> +
> + for_each_cpu(cpu, policy->related_cpus) {
> + cppc_fi = &per_cpu(cppc_freq_inv, cpu);
> + irq_work_sync(&cppc_fi->irq_work);
> + kthread_cancel_work_sync(&cppc_fi->work);
> + }
> +}
Yep, looks good (with its call on cppc_cpufreq_cpu_exit()).
Feel free to post V3 and I'll take an even closer look during testing.
Thanks,
Ionela.
> +
> +static void __init cppc_freq_invariance_init(void)
> +{
> + 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 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;
> +
> + ret = sched_setattr_nocheck(kworker_fie->task, &attr);
> + if (ret) {
> + pr_warn("%s: failed to set SCHED_DEADLINE: %d\n", __func__,
> + ret);
> + kthread_destroy_worker(kworker_fie);
> + return;
> + }
> +}
> +
> +static void cppc_freq_invariance_exit(void)
> +{
> + if (cppc_cpufreq_driver.get == hisi_cppc_cpufreq_get_rate)
> + return;
> +
> + kthread_destroy_worker(kworker_fie);
> + kworker_fie = NULL;
> +}
> +
> +#else
> +static inline int cppc_cpufreq_cpu_fie_init(struct cpufreq_policy *policy)
> +{
> + return 0;
> +}
> +
> +static inline void cppc_cpufreq_cpu_fie_exit(struct cpufreq_policy *policy)
> +{
> +}
> +
> +static inline void cppc_freq_invariance_init(void)
> +{
> +}
> +
> +static inline void cppc_freq_invariance_exit(void)
> +{
> +}
> +#endif /* CONFIG_ACPI_CPPC_CPUFREQ_FIE */
> +
> /* Callback function used to retrieve the max frequency from DMI */
> static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private)
> {
> @@ -324,11 +536,13 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
> cpu_data->perf_ctrls.desired_perf = caps->highest_perf;
>
> ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
> - if (ret)
> + if (ret) {
> pr_debug("Err setting perf value:%d on CPU:%d. ret:%d\n",
> caps->highest_perf, cpu, ret);
> + return ret;
> + }
>
> - return ret;
> + return cppc_cpufreq_cpu_fie_init(policy);
> }
>
> static int cppc_cpufreq_cpu_exit(struct cpufreq_policy *policy)
> @@ -338,6 +552,8 @@ static int cppc_cpufreq_cpu_exit(struct cpufreq_policy *policy)
> unsigned int cpu = policy->cpu;
> int ret;
>
> + cppc_cpufreq_cpu_fie_exit(policy);
> +
> cpu_data->perf_ctrls.desired_perf = caps->lowest_perf;
>
> ret = cppc_set_perf(cpu, &cpu_data->perf_ctrls);
> @@ -362,26 +578,35 @@ static inline u64 get_delta(u64 t1, u64 t0)
> return (u32)t1 - (u32)t0;
> }
>
> -static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu_data,
> - struct cppc_perf_fb_ctrs fb_ctrs_t0,
> - struct cppc_perf_fb_ctrs fb_ctrs_t1)
> +static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t0,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t1)
> {
> u64 delta_reference, delta_delivered;
> - u64 reference_perf, delivered_perf;
> + u64 reference_perf;
>
> - reference_perf = fb_ctrs_t0.reference_perf;
> + reference_perf = fb_ctrs_t0->reference_perf;
>
> - delta_reference = get_delta(fb_ctrs_t1.reference,
> - fb_ctrs_t0.reference);
> - delta_delivered = get_delta(fb_ctrs_t1.delivered,
> - fb_ctrs_t0.delivered);
> + delta_reference = get_delta(fb_ctrs_t1->reference,
> + fb_ctrs_t0->reference);
> + delta_delivered = get_delta(fb_ctrs_t1->delivered,
> + fb_ctrs_t0->delivered);
>
> - /* Check to avoid divide-by zero */
> - if (delta_reference || delta_delivered)
> - delivered_perf = (reference_perf * delta_delivered) /
> - delta_reference;
> - else
> - delivered_perf = cpu_data->perf_ctrls.desired_perf;
> + /* Check to avoid divide-by zero and invalid delivered_perf */
> + if (!delta_reference || !delta_delivered)
> + return cpu_data->perf_ctrls.desired_perf;
> +
> + return (reference_perf * delta_delivered) / delta_reference;
> +}
> +
> +static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu_data,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t0,
> + struct cppc_perf_fb_ctrs *fb_ctrs_t1)
> +{
> + u64 delivered_perf;
> +
> + delivered_perf = cppc_perf_from_fbctrs(cpu_data, fb_ctrs_t0,
> + fb_ctrs_t1);
>
> return cppc_cpufreq_perf_to_khz(cpu_data, delivered_perf);
> }
> @@ -405,7 +630,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
> if (ret)
> return ret;
>
> - return cppc_get_rate_from_fbctrs(cpu_data, fb_ctrs_t0, fb_ctrs_t1);
> + return cppc_get_rate_from_fbctrs(cpu_data, &fb_ctrs_t0, &fb_ctrs_t1);
> }
>
> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state)
> @@ -506,14 +731,21 @@ static void cppc_check_hisi_workaround(void)
>
> static int __init cppc_cpufreq_init(void)
> {
> + int ret;
> +
> if ((acpi_disabled) || !acpi_cpc_valid())
> return -ENODEV;
>
> INIT_LIST_HEAD(&cpu_data_list);
>
> cppc_check_hisi_workaround();
> + cppc_freq_invariance_init();
>
> - return cpufreq_register_driver(&cppc_cpufreq_driver);
> + ret = cpufreq_register_driver(&cppc_cpufreq_driver);
> + if (ret)
> + cppc_freq_invariance_exit();
> +
> + return ret;
> }
>
> static inline void free_cpu_data(void)
> @@ -531,6 +763,7 @@ static inline void free_cpu_data(void)
> static void __exit cppc_cpufreq_exit(void)
> {
> cpufreq_unregister_driver(&cppc_cpufreq_driver);
> + cppc_freq_invariance_exit();
>
> free_cpu_data();
> }
>
> --
> viresh
