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Rao" Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU Message-ID: <20200203045013.GC13468@in.ibm.com> References: <1574856072-30972-1-git-send-email-ego@linux.vnet.ibm.com> <1574856072-30972-3-git-send-email-ego@linux.vnet.ibm.com> <1575564547.si4rk0s96p.naveen@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1575564547.si4rk0s96p.naveen@linux.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-02-02_09:2020-02-02, 2020-02-02 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 adultscore=0 suspectscore=0 malwarescore=0 mlxscore=0 spamscore=0 mlxlogscore=999 clxscore=1015 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1911200001 definitions=main-2002030037 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: ego@linux.vnet.ibm.com Cc: Nathan Lynch , "Gautham R. Shenoy" , Tyrel Datwyler , linux-kernel@vger.kernel.org, Kamalesh Babulal , Vaidyanathan Srinivasan , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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.