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    SubjectRe: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU
    Gautham R. Shenoy wrote:
    > From: "Gautham R. Shenoy" <ego@linux.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@linux.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

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