linux-kernel - Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle

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Date:   Wed, 5 Feb 2020 08:08:46 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for
 every CPU



Le 27/11/2019 à 13:01, Gautham R. Shenoy a écrit :
> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> On Pseries LPARs, to calculate utilization, we need to know the
> [S]PURR ticks when the CPUs were busy or idle.
> 
> The total PURR and SPURR ticks are already exposed via the per-cpu
> sysfs files /sys/devices/system/cpu/cpuX/purr and
> /sys/devices/system/cpu/cpuX/spurr.
> 
> This patch adds support for exposing the idle PURR and SPURR ticks via
> /sys/devices/system/cpu/cpuX/idle_purr and
> /sys/devices/system/cpu/cpuX/idle_spurr.

Might be a candid question, but I see in arch/powerpc/kernel/time.c that 
PURR/SPURR are already taken into account by the kernel to calculate 
utilisation when CONFIG_VIRT_CPU_ACCOUNTING_NATIVE is selected.

As far as I understand, you are wanting to expose this to userland to 
redo the calculation there. What is wrong with the values reported by 
the kernel ?

Christophe

> 
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> ---
>   arch/powerpc/kernel/sysfs.c | 32 ++++++++++++++++++++++++++++++++
>   1 file changed, 32 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index 80a676d..42ade55 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -1044,6 +1044,36 @@ static ssize_t show_physical_id(struct device *dev,
>   }
>   static DEVICE_ATTR(physical_id, 0444, show_physical_id, NULL);
>   
> +static ssize_t idle_purr_show(struct device *dev,
> +			      struct device_attribute *attr, char *buf)
> +{
> +	struct cpu *cpu = container_of(dev, struct cpu, dev);
> +	unsigned int cpuid = cpu->dev.id;
> +	struct lppaca *cpu_lppaca_ptr = paca_ptrs[cpuid]->lppaca_ptr;
> +	u64 idle_purr_cycles = be64_to_cpu(cpu_lppaca_ptr->wait_state_cycles);
> +
> +	return sprintf(buf, "%llx\n", idle_purr_cycles);
> +}
> +static DEVICE_ATTR_RO(idle_purr);
> +
> +DECLARE_PER_CPU(u64, idle_spurr_cycles);
> +static ssize_t idle_spurr_show(struct device *dev,
> +			       struct device_attribute *attr, char *buf)
> +{
> +	struct cpu *cpu = container_of(dev, struct cpu, dev);
> +	unsigned int cpuid = cpu->dev.id;
> +	u64 *idle_spurr_cycles_ptr = per_cpu_ptr(&idle_spurr_cycles, cpuid);
> +
> +	return sprintf(buf, "%llx\n", *idle_spurr_cycles_ptr);
> +}
> +static DEVICE_ATTR_RO(idle_spurr);
> +
> +static void create_idle_purr_spurr_sysfs_entry(struct device *cpudev)
> +{
> +	device_create_file(cpudev, &dev_attr_idle_purr);
> +	device_create_file(cpudev, &dev_attr_idle_spurr);
> +}
> +
>   static int __init topology_init(void)
>   {
>   	int cpu, r;
> @@ -1067,6 +1097,8 @@ static int __init topology_init(void)
>   			register_cpu(c, cpu);
>   
>   			device_create_file(&c->dev, &dev_attr_physical_id);
> +			if (firmware_has_feature(FW_FEATURE_SPLPAR))
> +				create_idle_purr_spurr_sysfs_entry(&c->dev);
>   		}
>   	}
>   	r = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "powerpc/topology:online",
>