Messages in this thread |  | | Date | Wed, 5 Feb 2020 09:49:56 +0530 | From | Gautham R Shenoy <> | Subject | Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU |
| |
Hi Naveen,
On Tue, Feb 04, 2020 at 01:22:19PM +0530, Naveen N. Rao wrote: > Gautham R Shenoy wrote: > >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 ? > > Since it is possible for a cpu to go into extended cede for multiple seconds > during which time it is possible to mis-report utilization, I think it is > better to ensure that the sysfs interface for idle_[s]purr report the proper > values through use of IPI. >
Fair enough.
> With repect to lparstat, the read interval is user-specified and just gets > passed onto sleep().
Ok. So I guess currently you will be sending smp_call_function every time you read a PURR and SPURR. That number will now increase by 2 times when we read idle_purr and idle_spurr.
> > - Naveen >
-- Thanks and Regards gautham.
|  |