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


> -----Original Message-----
> From: Sudeep Holla [mailto:sudeep.holla@arm.com]
> Sent: 2014年4月15日 21:06
> To: Neil Zhang
> Cc: Will Deacon; linux@arm.linux.org.uk; Sudeep Holla;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: Re: [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.

Thanks for the comments.
I think it can help others if it can be accepted by mainline.

>
> 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.

Thanks for the detailed suggestions, I will refine it later.

>
> > +{
> > + 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


Best Regards,
Neil Zhang
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