Messages in this thread |  | | Date | Mon, 3 Feb 2020 10:20:14 +0530 | From | Gautham R Shenoy <> | Subject | Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU |
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Hi Naveen,
On Thu, Dec 05, 2019 at 10:23:58PM +0530, Naveen N. Rao wrote: > >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?
Yes, if the CPU whose idle_spurr cycle is being read is still in idle, then we will miss reporting the delta spurr cycles for this last idle-duration. Yes, we can use an smp_call_function_single(), though that will introduce IPI noise. How often will idle_[s]purr be read ?
> > - Naveen >
-- Thanks and Regards gautham.
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