[PATCH 4/7] x86/intel_rdt: Implement scheduling support for Intel RDT

[Vikas Shivappa]

Adds support for IA32_PQR_ASSOC MSR writes during task scheduling.

The high 32 bits in the per processor MSR IA32_PQR_ASSOC represents the
CLOSid. During context switch kernel implements this by writing the
CLOSid of the cgroup to which the task belongs to the CPU's
IA32_PQR_ASSOC MSR.

For Cache Allocation, this would let the task fill in the cache 'subset'
represented by the cgroup's Cache bit mask(CBM).

Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/intel_rdt.h | 54 ++++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/switch_to.h |  3 +++
 arch/x86/kernel/cpu/intel_rdt.c  |  3 +++
 kernel/sched/core.c              |  1 +
 kernel/sched/sched.h             |  3 +++
 5 files changed, 64 insertions(+)

diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
index 9e9dbbe..2fc496f 100644
--- a/arch/x86/include/asm/intel_rdt.h
+++ b/arch/x86/include/asm/intel_rdt.h
@@ -4,9 +4,13 @@
 #ifdef CONFIG_CGROUP_RDT
 
 #include <linux/cgroup.h>
+
+#define MSR_IA32_PQR_ASSOC		0xc8f
 #define MAX_CBM_LENGTH			32
 #define IA32_L3_CBM_BASE		0xc90
 #define CBM_FROM_INDEX(x)		(IA32_L3_CBM_BASE + x)
+DECLARE_PER_CPU(unsigned int, x86_cpu_clos);
+extern struct static_key rdt_enable_key;
 
 struct rdt_subsys_info {
 	/* Clos Bitmap to keep track of available CLOSids.*/
@@ -24,6 +28,11 @@ struct clos_cbm_map {
 	unsigned int clos_refcnt;
 };
 
+static inline bool rdt_enabled(void)
+{
+	return static_key_false(&rdt_enable_key);
+}
+
 /*
  * Return rdt group corresponding to this container.
  */
@@ -37,5 +46,50 @@ static inline struct intel_rdt *parent_rdt(struct intel_rdt *ir)
 	return css_rdt(ir->css.parent);
 }
 
+/*
+ * Return rdt group to which this task belongs.
+ */
+static inline struct intel_rdt *task_rdt(struct task_struct *task)
+{
+	return css_rdt(task_css(task, rdt_cgrp_id));
+}
+
+/*
+ * rdt_sched_in() - Writes the task's CLOSid to IA32_PQR_MSR
+ * if the current Closid is different than the new one.
+ */
+static inline void rdt_sched_in(struct task_struct *task)
+{
+	struct intel_rdt *ir;
+	unsigned int clos;
+
+	if (!rdt_enabled())
+		return;
+
+	/*
+	 * This needs to be fixed
+	 * to cache the whole PQR instead of just CLOSid.
+	 * PQR has closid in high 32 bits and CQM-RMID in low 10 bits.
+	 * Should not write a 0 to the low 10 bits of PQR
+	 * and corrupt RMID.
+	 */
+	clos = this_cpu_read(x86_cpu_clos);
+
+	rcu_read_lock();
+	ir = task_rdt(task);
+	if (ir->clos == clos) {
+		rcu_read_unlock();
+		return;
+	}
+
+	wrmsr(MSR_IA32_PQR_ASSOC, 0, ir->clos);
+	this_cpu_write(x86_cpu_clos, ir->clos);
+	rcu_read_unlock();
+}
+
+#else
+
+static inline void rdt_sched_in(struct task_struct *task) {}
+
 #endif
 #endif
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 751bf4b..82ef4b3 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -8,6 +8,9 @@ struct tss_struct;
 void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
 		      struct tss_struct *tss);
 
+#include <asm/intel_rdt.h>
+#define post_arch_switch(current)	rdt_sched_in(current)
+
 #ifdef CONFIG_X86_32
 
 #ifdef CONFIG_CC_STACKPROTECTOR
diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 58b39d6..74b1e28 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -34,6 +34,8 @@ static struct clos_cbm_map *ccmap;
 static struct rdt_subsys_info rdtss_info;
 static DEFINE_MUTEX(rdt_group_mutex);
 struct intel_rdt rdt_root_group;
+struct static_key __read_mostly rdt_enable_key = STATIC_KEY_INIT_FALSE;
+DEFINE_PER_CPU(unsigned int, x86_cpu_clos);
 
 /*
  * Mask of CPUs for writing CBM values. We only need one per-socket.
@@ -433,6 +435,7 @@ static int __init rdt_late_init(void)
 	__hotcpu_notifier(rdt_cpu_notifier, 0);
 
 	cpu_notifier_register_done();
+	static_key_slow_inc(&rdt_enable_key);
 	pr_info("Max bitmask length:%u,Max ClosIds: %u\n", cbm_len, maxid);
 
 	return 0;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f9123a8..cacb490 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2241,6 +2241,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
 	prev_state = prev->state;
 	vtime_task_switch(prev);
 	finish_arch_switch(prev);
+	post_arch_switch(current);
 	perf_event_task_sched_in(prev, current);
 	finish_lock_switch(rq, prev);
 	finish_arch_post_lock_switch();
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e0e1299..9153747 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1045,6 +1045,9 @@ static inline int task_on_rq_migrating(struct task_struct *p)
 #ifndef finish_arch_switch
 # define finish_arch_switch(prev)	do { } while (0)
 #endif
+#ifndef post_arch_switch
+# define post_arch_switch(current)	do { } while (0)
+#endif
 #ifndef finish_arch_post_lock_switch
 # define finish_arch_post_lock_switch()	do { } while (0)
 #endif
-- 
1.9.1

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