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b=t98xmY0NwaV1T1GEC5ruBk80D6UdsxwSsfFDaxsgvIM8wed7s2NLKSTKyoj77b029jUxYyifWvISuTENAPglCDvNypff0be68Qi5CMoFkIrUEwlUO4b2FbBJMcDqow3QCcmvkzicrkDNkzYRg1K/rpeLojJFX0WCefEaDGMrjqQ= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from IA0PPF9A76BB3A6.namprd12.prod.outlook.com (2603:10b6:20f:fc04::bdc) by PH0PR12MB999112.namprd12.prod.outlook.com (2603:10b6:510:38c::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9564.7; Thu, 29 Jan 2026 19:42:28 +0000 Received: from IA0PPF9A76BB3A6.namprd12.prod.outlook.com ([fe80::4d0e:603a:42fc:7c0]) by IA0PPF9A76BB3A6.namprd12.prod.outlook.com ([fe80::4d0e:603a:42fc:7c0%3]) with mapi id 15.20.9542.015; Thu, 29 Jan 2026 19:42:27 +0000 Message-ID: <57d7a46a-c3d6-4c7c-bed1-ee61d6d690fb@amd.com> Date: Thu, 29 Jan 2026 13:42:24 -0600 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 16/19] fs/resctrl: Implement rdtgroup_plza_write() to configure PLZA in a group To: "Luck, Tony" , Babu Moger Cc: corbet@lwn.net, reinette.chatre@intel.com, Dave.Martin@arm.com, james.morse@arm.com, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, akpm@linux-foundation.org, pawan.kumar.gupta@linux.intel.com, pmladek@suse.com, feng.tang@linux.alibaba.com, kees@kernel.org, arnd@arndb.de, fvdl@google.com, lirongqing@baidu.com, bhelgaas@google.com, seanjc@google.com, xin@zytor.com, manali.shukla@amd.com, dapeng1.mi@linux.intel.com, chang.seok.bae@intel.com, mario.limonciello@amd.com, naveen@kernel.org, elena.reshetova@intel.com, thomas.lendacky@amd.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, peternewman@google.com, eranian@google.com, gautham.shenoy@amd.com References: Content-Language: en-US From: Babu Moger In-Reply-To: Content-Type: text/plain; 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Also, ensure that only one group can have PLZA >> enabled at a time. >> > ... > >> +static ssize_t rdtgroup_plza_write(struct kernfs_open_file *of, char *buf, >> + size_t nbytes, loff_t off) >> +{ >> + struct rdt_resource *r = resctrl_arch_get_resource(RDT_RESOURCE_L3); >> + struct rdtgroup *rdtgrp, *prgrp; >> + int cpu, ret = 0; >> + bool enable; > ... > >> + /* Enable or disable PLZA state and update per CPU state if there is a change */ >> + if (enable != rdtgrp->plza) { >> + resctrl_arch_plza_setup(r, rdtgrp->closid, rdtgrp->mon.rmid); > What is this for? If I've just created a group with no tasks, and empty > CPU mask ... it seems that this writes the MSR_IA32_PQR_PLZA_ASSOC on > every CPU in every domain. > >> + for_each_cpu(cpu, &rdtgrp->cpu_mask) >> + resctrl_arch_set_cpu_plza(cpu, rdtgrp->closid, >> + rdtgrp->mon.rmid, enable); >> + rdtgrp->plza = enable; >> + } >> + >> +unlock: >> + rdtgroup_kn_unlock(of->kn); >> + >> + return ret ?: nbytes; >> +} > It also appears that marking a task as PLZA is permanent. Moving it to > another group doesn't unmark it. Is this intentional? > > # mkdir group1 group2 plza_group > # echo 1 > plza_group/plza > # echo $$ > group1/tasks > # echo $$ > plza_group/tasks > > My shell is now in group1 and in the plza_group > # grep $$ */tasks > group1/tasks:4125 > plza_group/tasks:4125 > > Move shell to group2 > # echo $$ > group2/tasks > # grep $$ */tasks > group2/tasks:4125 > plza_group/tasks:4125 > > Succcess in moving to group2, but still in plza_group You are moving the task from group1 to group2. This basically changes the association in MSR_IA32_PQR_ASSOC register, It does not change the PLZA association. To change it: a. You either remove task from plza group which triggers task update (tsk->plza = 0) echo >> /sys/fs/resctrl/plza_group/tasks b. Or you can change the group as regular group.   echo 0 > /sys/fs/resctrl/plza_group/plza Thanks for the trying it out. - Babu