[PATCH 3/3] x86/intel_rdt: Update closid in PQR_ASSOC registers in synchronous mode when changing "cpus"

[Fenghua Yu]

From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

When "cpus" is changed in a rdtgroup, the current code doesn't update
PQR_ASSOC registers with new closid in the cpus write operation.
The PQR_ASSOC registers are updated asynchronously later when new
processes are scheduled in on the CPUs.

A process may run on a CPU for long time without being switched to
another process, e.g. high performance computing or real time cases.
Then closid in the PQR_ASSOC register on the CPU is not updated for
long time until a new process is switched in.

This patch updates closid in PQR_ASSOC synchronously when writing
cpus to avoid the above issue.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 53 ++++++++++++++++++++------------
 1 file changed, 34 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 416b95e..a45f2ba 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -191,6 +191,31 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+/*
+ * MSR_IA32_PQR_ASSOC is scoped per logical CPU, so all updates
+ * are always in thread context.
+ */
+static void rdt_update_pqr_assoc_closid(void *v)
+{
+	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
+
+	state->closid = *(int *)v;
+	wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, state->closid);
+}
+
+static void rdt_update_pqr_assoc(const struct cpumask *cpu_mask, int closid)
+{
+	int cpu = get_cpu();
+
+	/* Update PQR_ASSOC MSR on this cpu if it's in cpu_mask. */
+	if (cpumask_test_cpu(cpu, cpu_mask))
+		rdt_update_pqr_assoc_closid(&closid);
+	/* Update PQR_ASSOC MSR on the rest of cpus. */
+	smp_call_function_many(cpu_mask, rdt_update_pqr_assoc_closid,
+			       &closid, 1);
+	put_cpu();
+}
+
 static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 				   char *buf, size_t nbytes, loff_t off)
 {
@@ -238,6 +263,9 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 			   &rdtgroup_default.cpu_mask, tmpmask);
 		for_each_cpu(cpu, tmpmask)
 			per_cpu(cpu_closid, cpu) = 0;
+
+		/* Update PQR_ASSOC registers on the dropped cpus */
+		rdt_update_pqr_assoc(tmpmask, rdtgroup_default.closid);
 	}
 
 	/*
@@ -253,6 +281,9 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
 		}
 		for_each_cpu(cpu, tmpmask)
 			per_cpu(cpu_closid, cpu) = rdtgrp->closid;
+
+		/* Update PQR_ASSOC registers on the added cpus */
+		rdt_update_pqr_assoc(tmpmask, rdtgrp->closid);
 	}
 
 	/* Done pushing/pulling - update this group with new mask */
@@ -783,18 +814,6 @@ static int reset_all_cbms(struct rdt_resource *r)
 }
 
 /*
- * MSR_IA32_PQR_ASSOC is scoped per logical CPU, so all updates
- * are always in thread context.
- */
-static void rdt_reset_pqr_assoc_closid(void *v)
-{
-	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
-
-	state->closid = 0;
-	wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, 0);
-}
-
-/*
  * Forcibly remove all of subdirectories under root.
  */
 static void rmdir_all_sub(void)
@@ -809,13 +828,9 @@ static void rmdir_all_sub(void)
 		t->closid = 0;
 	read_unlock(&tasklist_lock);
 
-	get_cpu();
-	/* Reset PQR_ASSOC MSR on this cpu. */
-	rdt_reset_pqr_assoc_closid(NULL);
-	/* Reset PQR_ASSOC MSR on the rest of cpus. */
-	smp_call_function_many(cpu_online_mask, rdt_reset_pqr_assoc_closid,
-			       NULL, 1);
-	put_cpu();
+	/* Reset PQR_ASSOC MSR on all online cpus */
+	rdt_update_pqr_assoc(cpu_online_mask, 0);
+
 	list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
 		/* Remove each rdtgroup other than root */
 		if (rdtgrp == &rdtgroup_default)
-- 
2.5.0