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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 4 Feb 2020 07:52:23 -0000 Received: from d06av24.portsmouth.uk.ibm.com (d06av24.portsmouth.uk.ibm.com [9.149.105.60]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 0147qLFh40960210 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 4 Feb 2020 07:52:21 GMT Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8E5C242049; Tue, 4 Feb 2020 07:52:21 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2D45842041; Tue, 4 Feb 2020 07:52:21 +0000 (GMT) Received: from localhost (unknown [9.199.60.222]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 4 Feb 2020 07:52:20 +0000 (GMT) Date: Tue, 04 Feb 2020 13:22:19 +0530 From: "Naveen N. Rao" Subject: Re: [PATCH 2/3] powerpc/sysfs: Show idle_purr and idle_spurr for every CPU To: ego@linux.vnet.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> <20200203045013.GC13468@in.ibm.com> In-Reply-To: <20200203045013.GC13468@in.ibm.com> MIME-Version: 1.0 User-Agent: astroid/v0.15-13-gb675b421 (https://github.com/astroidmail/astroid) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 x-cbid: 20020407-0008-0000-0000-0000034F8587 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20020407-0009-0000-0000-00004A70116E Message-Id: <1580802180.jpxk9s8apz.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-02-04_01:2020-02-04, 2020-02-04 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 adultscore=0 priorityscore=1501 malwarescore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 mlxscore=0 impostorscore=0 clxscore=1011 mlxlogscore=894 suspectscore=1 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1911200001 definitions=main-2002040057 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: , Cc: Nathan Lynch , 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" Gautham R Shenoy wrote: > Hi Naveen, >=20 > 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 *d= ev, >> > } >> > 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 =3D container_of(dev, struct cpu, dev); >> >+ unsigned int cpuid =3D cpu->dev.id; >> >+ struct lppaca *cpu_lppaca_ptr =3D paca_ptrs[cpuid]->lppaca_ptr; >> >+ u64 idle_purr_cycles =3D be64_to_cpu(cpu_lppaca_ptr->wait_state_cycle= s); >> >+ >> >+ 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 =3D container_of(dev, struct cpu, dev); >> >+ unsigned int cpuid =3D cpu->dev.id; >> >+ u64 *idle_spurr_cycles_ptr =3D per_cpu_ptr(&idle_spurr_cycles, cpuid)= ; >>=20 >> 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? >=20 > 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=20 seconds during which time it is possible to mis-report utilization, I=20 think it is better to ensure that the sysfs interface for idle_[s]purr=20 report the proper values through use of IPI. With repect to lparstat, the read interval is user-specified and just=20 gets passed onto sleep(). - Naveen