1 files changed, 72 insertions, 0 deletions
diff --git a/arch/x86/include/asm/intel_rdt_sched.h b/arch/x86/include/asm/intel_rdt_sched.h
new file mode 100644
index 000000000000..62a70bc85bce
--- /dev/null
+++ b/arch/x86/include/asm/intel_rdt_sched.h
@@ -0,0 +1,72 @@
+#ifndef _ASM_X86_INTEL_RDT_SCHED_H
+#define _ASM_X86_INTEL_RDT_SCHED_H
+
+#ifdef CONFIG_INTEL_RDT
+
+#include <linux/sched.h>
+#include <linux/jump_label.h>
+
+#define IA32_PQR_ASSOC	0x0c8f
+
+/**
+ * struct intel_pqr_state - State cache for the PQR MSR
+ * @rmid:		The cached Resource Monitoring ID
+ * @closid:		The cached Class Of Service ID
+ *
+ * The upper 32 bits of IA32_PQR_ASSOC contain closid and the
+ * lower 10 bits rmid. The update to IA32_PQR_ASSOC always
+ * contains both parts, so we need to cache them.
+ *
+ * The cache also helps to avoid pointless updates if the value does
+ * not change.
+ */
+struct intel_pqr_state {
+	u32			rmid;
+	u32			closid;
+};
+
+DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
+DECLARE_PER_CPU_READ_MOSTLY(int, cpu_closid);
+DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
+
+/*
+ * intel_rdt_sched_in() - Writes the task's CLOSid to IA32_PQR_MSR
+ *
+ * Following considerations are made so that this has minimal impact
+ * on scheduler hot path:
+ * - This will stay as no-op unless we are running on an Intel SKU
+ *   which supports resource control and we enable by mounting the
+ *   resctrl file system.
+ * - Caches the per cpu CLOSid values and does the MSR write only
+ *   when a task with a different CLOSid is scheduled in.
+ *
+ * Must be called with preemption disabled.
+ */
+static inline void intel_rdt_sched_in(void)
+{
+	if (static_branch_likely(&rdt_enable_key)) {
+		struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
+		int closid;
+
+		/*
+		 * If this task has a closid assigned, use it.
+		 * Else use the closid assigned to this cpu.
+		 */
+		closid = current->closid;
+		if (closid == 0)
+			closid = this_cpu_read(cpu_closid);
+
+		if (closid != state->closid) {
+			state->closid = closid;
+			wrmsr(IA32_PQR_ASSOC, state->rmid, closid);
+		}
+	}
+}
+
+#else
+
+static inline void intel_rdt_sched_in(void) {}
+
+#endif /* CONFIG_INTEL_RDT */
+
+#endif /* _ASM_X86_INTEL_RDT_SCHED_H */