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

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Date:   Thu, 05 Dec 2019 22:23:58 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for
 every CPU

Gautham R. Shenoy wrote:
> 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.
> 
> 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);

Is it possible for a user to read stale values if a particular cpu is in 
an extended cede? Is it possible to use smp_call_function_single() to 
force the cpu out of idle?

- Naveen