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Date: Tue, 04 Feb 2020 13:22:19 +0530 From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> To: ego@...ux.vnet.ibm.com Cc: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>, linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 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> Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU 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. With repect to lparstat, the read interval is user-specified and just gets passed onto sleep(). - Naveen
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