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Sun, 15 Sep 2019 07:42:22 +0000 Received: from b01ledav004.gho.pok.ibm.com (b01ledav004.gho.pok.ibm.com [9.57.199.109]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x8F7gLdc42008958 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sun, 15 Sep 2019 07:42:21 GMT Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C6678112062; Sun, 15 Sep 2019 07:42:21 +0000 (GMT) Received: from b01ledav004.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7F466112061; Sun, 15 Sep 2019 07:42:21 +0000 (GMT) Received: from sofia.ibm.com (unknown [9.85.81.174]) by b01ledav004.gho.pok.ibm.com (Postfix) with ESMTP; Sun, 15 Sep 2019 07:42:21 +0000 (GMT) Received: by sofia.ibm.com (Postfix, from userid 1000) id 8E54F2E2D63; Sun, 15 Sep 2019 13:12:17 +0530 (IST) Date: Sun, 15 Sep 2019 13:12:17 +0530 From: Gautham R Shenoy To: Nathan Lynch Subject: Re: [PATCH 0/2] pseries/hotplug: Change the default behaviour of cede_offline Message-ID: <20190915074217.GA943@in.ibm.com> References: <1568284541-15169-1-git-send-email-ego@linux.vnet.ibm.com> <87impxr0am.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87impxr0am.fsf@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:, , definitions=2019-09-15_03:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1909150084 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: "Gautham R. Shenoy" , Tyrel Datwyler , "Aneesh Kumar K.V" , Kamalesh Babulal , linux-kernel@vger.kernel.org, Nicholas Piggin , "Naveen N . Rao" , Vaidyanathan Srinivasan , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hello Nathan, On Thu, Sep 12, 2019 at 10:39:45AM -0500, Nathan Lynch wrote: > "Gautham R. Shenoy" writes: > > The patchset also defines a new sysfs attribute > > "/sys/device/system/cpu/cede_offline_enabled" on PSeries Linux guests > > to allow userspace programs to change the state into which the > > offlined CPU need to be put to at runtime. > > A boolean sysfs interface will become awkward if we need to add another > mode in the future. > > What do you think about naming the attribute something like > 'offline_mode', with the possible values 'extended-cede' and > 'rtas-stopped'? We can do that. However, IMHO in the longer term, on PSeries guests, we should have only one offline state - rtas-stopped. The reason for this being, that on Linux, SMT switch is brought into effect through the CPU Hotplug interface. The only state in which the SMT switch will recognized by the hypervisors such as PHYP is rtas-stopped. All other states (such as extended-cede) should in the long-term be exposed via the cpuidle interface. With this in mind, I made the sysfs interface boolean to mirror the current "cede_offline" commandline parameter. Eventually when we have only one offline-state, we can deprecate the commandline parameter as well as the sysfs interface. Thoughts? -- Thanks and Regards gautham.