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Fri, 6 Sep 2019 21:34:58 +0000 (GMT) Received: from b03ledav002.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A3BFF136051; Fri, 6 Sep 2019 21:34:58 +0000 (GMT) Received: from localhost (unknown [9.41.101.192]) by b03ledav002.gho.boulder.ibm.com (Postfix) with ESMTP; Fri, 6 Sep 2019 21:34:58 +0000 (GMT) From: Nathan Lynch To: Srikar Dronamraju Subject: Re: [PATCH v2 3/4] powerpc/numa: Early request for home node associativity In-Reply-To: <20190906034110.GA12412@linux.vnet.ibm.com> References: <20190829055023.6171-1-srikar@linux.vnet.ibm.com> <20190829055023.6171-4-srikar@linux.vnet.ibm.com> <87tv9qqzm7.fsf@linux.ibm.com> <20190906034110.GA12412@linux.vnet.ibm.com> Date: Fri, 06 Sep 2019 16:34:58 -0500 Message-ID: <87r24tqfb1.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=2019-09-06_09:, , 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=8.0.1-1906280000 definitions=main-1909060217 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: Satheesh Rajendran , linuxppc-dev , Nicholas Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Srikar Dronamraju writes: >> Regardless, I have an annoying question :-) Isn't it possible that, >> while Linux is calling vphn_get_nid() for each logical cpu in sequence, >> the platform could change a virtual processor's node assignment, >> potentially causing sibling threads to get different node assignments >> and producing an incoherent topology (which then leads to sched domain >> assertions etc)? >> > > Right, its certainly possible for node assignment to change while we iterate > through the siblings. Do you have an recommendations? > >> If so, I think more care is needed. The algorithm should make the vphn >> call only once per cpu node, I think? > > I didn't get "once per cpu node", How do we know which all cpus are part of > that cpu node? Or did you mean once per cpu core? Sorry, "node" is overloaded in this context. I meant once per cpu device node from the device tree, each of which I believe corresponds to a core, yes.