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SubjectRe: [PATCH v2] ARM: perf: save/restore pmu registers in pm notifier
Hi Will,

Thanks for the response.

Hi Neil,

On 14/04/14 02:42, Neil Zhang wrote:
> From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
>
> This adds core support for saving and restoring CPU PMU registers
> for suspend/resume support i.e. deeper C-states in cpuidle terms.
> This patch adds support only to ARMv7 PMU registers save/restore.
> It needs to be extended to xscale and ARMv6 if needed.
>
> [Neil] We found that DS-5 not work on our CA7 based SoCs.
> After debuging, found PMU registers were lost because of core power down.
> Then i found Sudeep had a patch to fix it about two years ago but not in
> the mainline, just port it.
>

The patch was written as PoC to support multiple PMUs back then and was clearly
not intended for upstream. Will has already mentioned what this patch needs to
improve on.

I have mentioned few comments which IMO is necessary.

> Signed-off-by: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
> Signed-off-by: Neil Zhang <zhangwm@marvell.com>
> ---
> arch/arm/include/asm/pmu.h | 11 +++++++++
> arch/arm/kernel/perf_event_cpu.c | 29 ++++++++++++++++++++++-
> arch/arm/kernel/perf_event_v7.c | 47 ++++++++++++++++++++++++++++++++++++++
> 3 files changed, 86 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/pmu.h b/arch/arm/include/asm/pmu.h
> index ae1919b..f37f048 100644
> --- a/arch/arm/include/asm/pmu.h
> +++ b/arch/arm/include/asm/pmu.h
> @@ -62,6 +62,15 @@ struct pmu_hw_events {
> raw_spinlock_t pmu_lock;
> };
>
> +struct cpupmu_regs {
> + u32 pmc;
> + u32 pmcntenset;
> + u32 pmuseren;
> + u32 pmintenset;
> + u32 pmxevttype[8];
> + u32 pmxevtcnt[8];
> +};
> +

This can't be generic, it needs to be specific to each PMU implementations.
I have clearly mentioned it in the commit log. It's better to move this out
to each PMU specific implementations.

> struct arm_pmu {
> struct pmu pmu;
> cpumask_t active_irqs;
> @@ -83,6 +92,8 @@ struct arm_pmu {
> int (*request_irq)(struct arm_pmu *, irq_handler_t handler);
> void (*free_irq)(struct arm_pmu *);
> int (*map_event)(struct perf_event *event);
> + void (*save_regs)(struct arm_pmu *, struct cpupmu_regs *);
> + void (*restore_regs)(struct arm_pmu *, struct cpupmu_regs *);

Once cpupmu_regs becomes PMU specific, you can remove it from the above 2
function pointers.

> int num_events;
> atomic_t active_events;
> struct mutex reserve_mutex;
> diff --git a/arch/arm/kernel/perf_event_cpu.c b/arch/arm/kernel/perf_event_cpu.c
> index 51798d7..7f1c756 100644
> --- a/arch/arm/kernel/perf_event_cpu.c
> +++ b/arch/arm/kernel/perf_event_cpu.c
> @@ -19,6 +19,7 @@
> #define pr_fmt(fmt) "CPU PMU: " fmt
>
> #include <linux/bitmap.h>
> +#include <linux/cpu_pm.h>
> #include <linux/export.h>
> #include <linux/kernel.h>
> #include <linux/of.h>
> @@ -39,6 +40,7 @@ static DEFINE_PER_CPU(struct arm_pmu *, percpu_pmu);
> static DEFINE_PER_CPU(struct perf_event * [ARMPMU_MAX_HWEVENTS], hw_events);
> static DEFINE_PER_CPU(unsigned long [BITS_TO_LONGS(ARMPMU_MAX_HWEVENTS)], used_mask);
> static DEFINE_PER_CPU(struct pmu_hw_events, cpu_hw_events);
> +static DEFINE_PER_CPU(struct cpupmu_regs, cpu_pmu_regs);
>
> /*
> * Despite the names, these two functions are CPU-specific and are used
> @@ -217,6 +219,23 @@ static struct notifier_block cpu_pmu_hotplug_notifier = {
> .notifier_call = cpu_pmu_notify,
> };
>
> +static int cpu_pmu_pm_notify(struct notifier_block *b,
> + unsigned long action, void *hcpu)

hcpu is misleading, the cpu_pm_notify doesn't pass the logical cpu index.
IIRC its NULL, rename it.

> +{
> + struct cpupmu_regs *pmuregs = this_cpu_ptr(&cpu_pmu_regs);
> +
> + if (action == CPU_PM_ENTER && cpu_pmu->save_regs)
> + cpu_pmu->save_regs(cpu_pmu, pmuregs);
> + else if (action == CPU_PM_EXIT && cpu_pmu->restore_regs)
> + cpu_pmu->restore_regs(cpu_pmu, pmuregs);
> +
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block cpu_pmu_pm_notifier = {
> + .notifier_call = cpu_pmu_pm_notify,
> +};
> +
> /*
> * PMU platform driver and devicetree bindings.
> */
> @@ -349,9 +368,17 @@ static int __init register_pmu_driver(void)
> if (err)
> return err;
>
> + err = cpu_pm_register_notifier(&cpu_pmu_pm_notifier);
> + if (err) {
> + unregister_cpu_notifier(&cpu_pmu_hotplug_notifier);
> + return err;
> + }
> +
> err = platform_driver_register(&cpu_pmu_driver);
> - if (err)
> + if (err) {
> + cpu_pm_unregister_notifier(&cpu_pmu_pm_notifier);
> unregister_cpu_notifier(&cpu_pmu_hotplug_notifier);
> + }
>
> return err;
> }
> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
> index f4ef398..29ae8f1 100644
> --- a/arch/arm/kernel/perf_event_v7.c
> +++ b/arch/arm/kernel/perf_event_v7.c
> @@ -1237,6 +1237,51 @@ static void armv7_pmnc_dump_regs(struct arm_pmu *cpu_pmu)
> }
> #endif
>
> +static void armv7pmu_save_regs(struct arm_pmu *cpu_pmu,
> + struct cpupmu_regs *regs)
> +{
> + unsigned int cnt;
> + asm volatile("mrc p15, 0, %0, c9, c12, 0" : "=r" (regs->pmc));
> + if (!(regs->pmc & ARMV7_PMNC_E))
> + return;
> +
> + asm volatile("mrc p15, 0, %0, c9, c12, 1" : "=r" (regs->pmcntenset));
> + asm volatile("mrc p15, 0, %0, c9, c14, 0" : "=r" (regs->pmuseren));
> + asm volatile("mrc p15, 0, %0, c9, c14, 1" : "=r" (regs->pmintenset));
> + asm volatile("mrc p15, 0, %0, c9, c13, 0" : "=r" (regs->pmxevtcnt[0]));
> + for (cnt = ARMV7_IDX_COUNTER0;
> + cnt <= ARMV7_IDX_COUNTER_LAST(cpu_pmu); cnt++) {

As Will suggested better to use used_mask to save/restore only active events.

Regards,
Sudeep



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