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Shenoy" Subject: Re: [PATCH v2 1/1] pseries/hotplug-cpu: Change default behaviour of cede_offline to "off" In-Reply-To: <1571740391-3251-2-git-send-email-ego@linux.vnet.ibm.com> References: <1571740391-3251-1-git-send-email-ego@linux.vnet.ibm.com> <1571740391-3251-2-git-send-email-ego@linux.vnet.ibm.com> Date: Thu, 31 Oct 2019 11:30:11 -0500 Message-ID: <87k18klvxo.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-10-31_06:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 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-1910310164 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: Tyrel Datwyler , Kamalesh Babulal , linux-kernel@vger.kernel.org, Nicholas Piggin , "Aneesh Kumar K.V" , "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" "Gautham R. Shenoy" writes: > From: "Gautham R. Shenoy" > > Currently on PSeries Linux guests, the offlined CPU can be put to one > of the following two states: > - Long term processor cede (also called extended cede) > - Returned to the hypervisor via RTAS "stop-self" call. > > This is controlled by the kernel boot parameter "cede_offline=on/off". > > By default the offlined CPUs enter extended cede. The PHYP hypervisor > considers CPUs in extended cede to be "active" since they are still > under the control fo the Linux guests. Hence, when we change the SMT > modes by offlining the secondary CPUs, the PURR and the RWMR SPRs will > continue to count the values for offlined CPUs in extended cede as if > they are online. This breaks the accounting in tools such as lparstat. > > To fix this, ensure that by default the offlined CPUs are returned to > the hypervisor via RTAS "stop-self" call by changing the default value > of "cede_offline_enabled" to false. > > Fixes: commit 3aa565f53c39 ("powerpc/pseries: Add hooks to put the CPU > into an appropriate offline state") > > Signed-off-by: Gautham R. Shenoy I'm OK with changing the default as a precursor to removing the code that implements the cede offline mode. Acked-by: Nathan Lynch