linux-kernel - [RFC PATCH 17/19] fs/resctrl: Update PLZA configuration when cpu

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Message-ID: <f2afd52c55edaedbe410274065049d90a763a136.1769029977.git.babu.moger@amd.com>
Date: Wed, 21 Jan 2026 15:12:55 -0600
From: Babu Moger <babu.moger@....com>
To: <corbet@....net>, <tony.luck@...el.com>, <reinette.chatre@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <babu.moger@....com>,
	<tglx@...nel.org>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
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Subject: [RFC PATCH 17/19] fs/resctrl: Update PLZA configuration when cpu_mask changes

When PLZA is active for a resctrl group, per-CPU PLZA state must track CPU
mask changes.

Introduce cpus_ctrl_plza_write() to update PLZA on CPUs entering or leaving
the group.

Signed-off-by: Babu Moger <babu.moger@....com>
---
 fs/resctrl/rdtgroup.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 042ae7d63aea..bea017f9bd40 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -508,6 +508,33 @@ static int cpus_ctrl_write(struct rdtgroup *rdtgrp, cpumask_var_t newmask,
 	return 0;
 }
 
+static int cpus_ctrl_plza_write(struct rdtgroup *rdtgrp, cpumask_var_t newmask,
+				cpumask_var_t tmpmask)
+{
+	int cpu;
+
+	/* Check if the cpus are dropped from the group */
+	cpumask_andnot(tmpmask, &rdtgrp->cpu_mask, newmask);
+	if (!cpumask_empty(tmpmask)) {
+		for_each_cpu(cpu, tmpmask)
+			resctrl_arch_set_cpu_plza(cpu, rdtgrp->closid,
+						  rdtgrp->mon.rmid, false);
+	}
+
+	/* If the CPUs are added then enable PLZA on the added CPUs. */
+	cpumask_andnot(tmpmask, newmask, &rdtgrp->cpu_mask);
+	if (!cpumask_empty(tmpmask)) {
+		for_each_cpu(cpu, tmpmask)
+			resctrl_arch_set_cpu_plza(cpu, rdtgrp->closid,
+						  rdtgrp->mon.rmid, true);
+	}
+
+	/* Update the group with new mask */
+	cpumask_copy(&rdtgrp->cpu_mask, newmask);
+
+	return 0;
+}
+
 static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 				   char *buf, size_t nbytes, loff_t off)
 {
@@ -563,7 +590,9 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		goto unlock;
 	}
 
-	if (rdtgrp->type == RDTCTRL_GROUP)
+	if (rdtgrp->plza)
+		ret = cpus_ctrl_plza_write(rdtgrp, newmask, tmpmask);
+	else if (rdtgrp->type == RDTCTRL_GROUP)
 		ret = cpus_ctrl_write(rdtgrp, newmask, tmpmask, tmpmask1);
 	else if (rdtgrp->type == RDTMON_GROUP)
 		ret = cpus_mon_write(rdtgrp, newmask, tmpmask);
-- 
2.34.1