From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E487C433ED for ; Wed, 5 May 2021 14:39:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4AC3613C3 for ; Wed, 5 May 2021 14:39:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233271AbhEEOkp (ORCPT ); Wed, 5 May 2021 10:40:45 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:46222 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S232919AbhEEOkn (ORCPT ); Wed, 5 May 2021 10:40:43 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 145EXOsm167381; Wed, 5 May 2021 10:39:28 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=pp1; bh=Lc7uFzgPNhcsp+WarEELqYO8Kt7OXRxKAZ/JSIHieH0=; b=IvWsmmuKvc1ZrmXnxYchok7nblZeFztREwnqJ4MePoTGwubYRGcX5ziJ6YS/wGWtnrRG 4RJ4IcpZ1PR5iIY1jYxuxJcszxtQ1XOZV2Zoup8SQY/3sS5vghCCVcFlliQX4rZbA4Mq 0Xyd6KnWMeUNSJNOw3qIsZF5oULnT23UXwLtle2iFWycijSMCTwMhTDlr3U+UMTgZtbM 2tiv2AZCQrZoJkQQmG7wmelLF42awMKrqYs89Y8NI+jXjILujGXkuZLvKaCU8TXqXDl4 Lne6xfC/VZ4apgMQ5QAR/JR+rbBg9lpKqmnukkY7zfwTq2XqIHTkvHUIJgQslLiHO2x2 vA== Received: from ppma03ams.nl.ibm.com (62.31.33a9.ip4.static.sl-reverse.com [169.51.49.98]) by mx0b-001b2d01.pphosted.com with ESMTP id 38bw4nrck1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 05 May 2021 10:39:28 -0400 Received: from pps.filterd (ppma03ams.nl.ibm.com [127.0.0.1]) by ppma03ams.nl.ibm.com (8.16.0.43/8.16.0.43) with SMTP id 145EcIss012554; Wed, 5 May 2021 14:39:27 GMT Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by ppma03ams.nl.ibm.com with ESMTP id 38bedxrbtq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 05 May 2021 14:39:26 +0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 145EdORw2753238 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 5 May 2021 14:39:24 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 093144C052; Wed, 5 May 2021 14:39:24 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C09944C040; Wed, 5 May 2021 14:39:23 +0000 (GMT) Received: from pomme.local (unknown [9.145.1.8]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 5 May 2021 14:39:23 +0000 (GMT) Subject: Re: [PATCH v4] pseries/drmem: update LMBs after LPM To: Nathan Lynch Cc: Tyrel Datwyler , linux-kernel@vger.kernel.org, paulus@samba.org, "Aneesh Kumar K . V" , linuxppc-dev@lists.ozlabs.org References: <20210504092038.8514-1-ldufour@linux.ibm.com> <87bl9qf7xk.fsf@linux.ibm.com> From: Laurent Dufour Message-ID: <8cebddd7-5b06-ba93-3cc7-9cdab57db491@linux.ibm.com> Date: Wed, 5 May 2021 16:39:23 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <87bl9qf7xk.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: BShm9QQKfxlfhzv9-PAaRod7W6k6SlW9 X-Proofpoint-ORIG-GUID: BShm9QQKfxlfhzv9-PAaRod7W6k6SlW9 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.761 definitions=2021-05-05_09:2021-05-05,2021-05-05 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 adultscore=0 mlxscore=0 phishscore=0 spamscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 lowpriorityscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104060000 definitions=main-2105050106 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 05/05/2021 à 00:30, Nathan Lynch a écrit : > Hi Laurent, Hi Nathan, Thanks for your review. > Bear with me while I work through the commit message: > > Laurent Dufour writes: >> After a LPM, the device tree node ibm,dynamic-reconfiguration-memory may be >> updated by the hypervisor in the case the NUMA topology of the LPAR's >> memory is updated. > > Yes, the RTAS functions ibm,update-nodes and ibm,update-properties, > which the OS invokes after resuming, may bring in updated properties > under the ibm,dynamic-reconfiguration-memory node, including the > ibm,associativity-lookup-arrays property. > >> This is caught by the kernel, > > "Caught" makes me think this is an error condition, as in catching an > exception. I guess "handled" better conveys your meaning? ok > >> but the memory's node is updated because >> there is no way to move a memory block between nodes. > > "The memory's node" refers the ibm,dynamic-reconfiguration-memory DT > node, yes? Or is it referring to Linux's NUMA nodes? ("move a memory > block between nodes" in your statement here refers to Linux's NUMA > nodes, that much is clear to me.) > > I am failing to follow the cause->effect relationship stated. True, > changing a block's node assignment while it's in use isn't safe. I don't > see why that implies that "the memory's node is updated"? In fact this > seems contradictory. > > This statement makes more sense to me if I change it to "the memory's > node is _not_ updated" -- is this what you intended? Correct, I dropped the 'not' word here ;) > >> If later a memory block is added or removed, drmem_update_dt() is called >> and it is overwriting the DT node to match the added or removed LMB. > > I understand this, but I will expand on it. > > dlpar_memory() > -> dlpar_memory_add_by_count() > -> dlpar_add_lmb() > -> update_lmb_associativity_index() > ... lmb->aa_index = > -> drmem_update_dt() > > update_lmb_associativity_index() retrieves the firmware description of > the new block, and sets the aa_index of the matching entry in the > drmem_info array to the value matching the firmware description. > > Then, drmem_update_dt() walks the drmem_info array and synthesizes a new > /ibm,dynamic-reconfiguration-memory/ibm,dynamic-memory-v2 property based > on the recently updated information in that array. Yes > >> But the LMB's associativity node has not been updated after the DT >> node update and thus the node is overwritten by the Linux's topology >> instead of the hypervisor one. > > So, an example of the problem is: > > 1. VM migrates. On resume, ibm,associativity-lookup-arrays is changed > via ibm,update-properties. Entries in the drmem_info array remain > unchanged, with aa_index values that correspond to the source > system's ibm,associativity-lookup-arrays property, now inaccessible. > > 2. A memory block is added. We look up the new block's entry in the > drmem_info array, and set the aa_index to the value matching the > current ibm,associativity-lookup-arrays. > > 3. Then, the ibm,associativity-lookup-arrays property is completely > regenerated from the drmem_info array, which reflects a mixture of > information from the source and destination systems. > > Do I understand correctly? Yes > > >> Introduce a hook called when the ibm,dynamic-reconfiguration-memory node is >> updated to force an update of the LMB's associativity. However, ignore the >> call to that hook when the update has been triggered by drmem_update_dt(). >> Because, in that case, the LMB tree has been used to set the DT property >> and thus it doesn't need to be updated back. Since drmem_update_dt() is >> called under the protection of the device_hotplug_lock and the hook is >> called in the same context, use a simple boolean variable to detect that >> call. > > This strikes me as almost a revert of e978a3ccaa71 ("powerpc/pseries: > remove obsolete memory hotplug DT notifier code"). Not really identical to reverting e978a3ccaa71, here only the aa_index of the LMB is updated, everything else is kept in place. I don't try to apply the memory layout's changes, just updating the in use LMB's aa_index field. The only matching point with the code reverted by the commit you mentioned would be the use of a global variable in_drmem_update instead of the previous rtas_hp_event to prevent the LMB tree to be updated again during memory hot plug event. > I'd rather avoid smuggling through global state information that ought > to be passed in function parameters, if it should be passed around at > all. Despite having (IMO) relatively simple responsibilities, this code > is difficult to change and review; adding this property makes it > worse. If the structure of the code is pushing us toward this kind of > compromise, then the code probably needs more fundamental changes. > > I'm probably forgetting something -- can anyone remind me why we need an > array of these: > > struct drmem_lmb { > u64 base_addr; > u32 drc_index; > u32 aa_index; > u32 flags; > }; > > which is just a less efficient representation of what's already in the > device tree? If we got rid of it, would this problem disappear? I don't think this is right for the moment, at first, we should robustify the DLPAR and LPM operations. 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Wed, 5 May 2021 14:39:23 +0000 (GMT) Received: from pomme.local (unknown [9.145.1.8]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 5 May 2021 14:39:23 +0000 (GMT) Subject: Re: [PATCH v4] pseries/drmem: update LMBs after LPM To: Nathan Lynch References: <20210504092038.8514-1-ldufour@linux.ibm.com> <87bl9qf7xk.fsf@linux.ibm.com> From: Laurent Dufour Message-ID: <8cebddd7-5b06-ba93-3cc7-9cdab57db491@linux.ibm.com> Date: Wed, 5 May 2021 16:39:23 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <87bl9qf7xk.fsf@linux.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: BShm9QQKfxlfhzv9-PAaRod7W6k6SlW9 X-Proofpoint-ORIG-GUID: BShm9QQKfxlfhzv9-PAaRod7W6k6SlW9 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391, 18.0.761 definitions=2021-05-05_09:2021-05-05, 2021-05-05 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 adultscore=0 mlxscore=0 phishscore=0 spamscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 lowpriorityscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104060000 definitions=main-2105050106 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 , linuxppc-dev@lists.ozlabs.org, paulus@samba.org, linux-kernel@vger.kernel.org, "Aneesh Kumar K . V" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 05/05/2021 à 00:30, Nathan Lynch a écrit : > Hi Laurent, Hi Nathan, Thanks for your review. > Bear with me while I work through the commit message: > > Laurent Dufour writes: >> After a LPM, the device tree node ibm,dynamic-reconfiguration-memory may be >> updated by the hypervisor in the case the NUMA topology of the LPAR's >> memory is updated. > > Yes, the RTAS functions ibm,update-nodes and ibm,update-properties, > which the OS invokes after resuming, may bring in updated properties > under the ibm,dynamic-reconfiguration-memory node, including the > ibm,associativity-lookup-arrays property. > >> This is caught by the kernel, > > "Caught" makes me think this is an error condition, as in catching an > exception. I guess "handled" better conveys your meaning? ok > >> but the memory's node is updated because >> there is no way to move a memory block between nodes. > > "The memory's node" refers the ibm,dynamic-reconfiguration-memory DT > node, yes? Or is it referring to Linux's NUMA nodes? ("move a memory > block between nodes" in your statement here refers to Linux's NUMA > nodes, that much is clear to me.) > > I am failing to follow the cause->effect relationship stated. True, > changing a block's node assignment while it's in use isn't safe. I don't > see why that implies that "the memory's node is updated"? In fact this > seems contradictory. > > This statement makes more sense to me if I change it to "the memory's > node is _not_ updated" -- is this what you intended? Correct, I dropped the 'not' word here ;) > >> If later a memory block is added or removed, drmem_update_dt() is called >> and it is overwriting the DT node to match the added or removed LMB. > > I understand this, but I will expand on it. > > dlpar_memory() > -> dlpar_memory_add_by_count() > -> dlpar_add_lmb() > -> update_lmb_associativity_index() > ... lmb->aa_index = > -> drmem_update_dt() > > update_lmb_associativity_index() retrieves the firmware description of > the new block, and sets the aa_index of the matching entry in the > drmem_info array to the value matching the firmware description. > > Then, drmem_update_dt() walks the drmem_info array and synthesizes a new > /ibm,dynamic-reconfiguration-memory/ibm,dynamic-memory-v2 property based > on the recently updated information in that array. Yes > >> But the LMB's associativity node has not been updated after the DT >> node update and thus the node is overwritten by the Linux's topology >> instead of the hypervisor one. > > So, an example of the problem is: > > 1. VM migrates. On resume, ibm,associativity-lookup-arrays is changed > via ibm,update-properties. Entries in the drmem_info array remain > unchanged, with aa_index values that correspond to the source > system's ibm,associativity-lookup-arrays property, now inaccessible. > > 2. A memory block is added. We look up the new block's entry in the > drmem_info array, and set the aa_index to the value matching the > current ibm,associativity-lookup-arrays. > > 3. Then, the ibm,associativity-lookup-arrays property is completely > regenerated from the drmem_info array, which reflects a mixture of > information from the source and destination systems. > > Do I understand correctly? Yes > > >> Introduce a hook called when the ibm,dynamic-reconfiguration-memory node is >> updated to force an update of the LMB's associativity. However, ignore the >> call to that hook when the update has been triggered by drmem_update_dt(). >> Because, in that case, the LMB tree has been used to set the DT property >> and thus it doesn't need to be updated back. Since drmem_update_dt() is >> called under the protection of the device_hotplug_lock and the hook is >> called in the same context, use a simple boolean variable to detect that >> call. > > This strikes me as almost a revert of e978a3ccaa71 ("powerpc/pseries: > remove obsolete memory hotplug DT notifier code"). Not really identical to reverting e978a3ccaa71, here only the aa_index of the LMB is updated, everything else is kept in place. I don't try to apply the memory layout's changes, just updating the in use LMB's aa_index field. The only matching point with the code reverted by the commit you mentioned would be the use of a global variable in_drmem_update instead of the previous rtas_hp_event to prevent the LMB tree to be updated again during memory hot plug event. > I'd rather avoid smuggling through global state information that ought > to be passed in function parameters, if it should be passed around at > all. Despite having (IMO) relatively simple responsibilities, this code > is difficult to change and review; adding this property makes it > worse. If the structure of the code is pushing us toward this kind of > compromise, then the code probably needs more fundamental changes. > > I'm probably forgetting something -- can anyone remind me why we need an > array of these: > > struct drmem_lmb { > u64 base_addr; > u32 drc_index; > u32 aa_index; > u32 flags; > }; > > which is just a less efficient representation of what's already in the > device tree? If we got rid of it, would this problem disappear? I don't think this is right for the moment, at first, we should robustify the DLPAR and LPM operations.