[PATCH 5/7] x86/intel_rdt: Software Cache for IA32_PQR_MSR

[Vikas Shivappa]

This patch implements a common software cache for IA32_PQR_MSR(RMID 0:9,
    CLOSId 32:63) to be used by both CMT and CAT. CMT updates the RMID
where as CAT updates the CLOSid in the software cache. When the new
RMID/CLOSid value is different from the cached values, IA32_PQR_MSR is
updated. Since the measured rdmsr latency for IA32_PQR_MSR is very
high(~250 cycles) this software cache is necessary to avoid reading the
MSR to compare the current CLOSid value.
During CPU hotplug the pqr cache is updated to zero.

Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>

Conflicts:
	arch/x86/kernel/cpu/perf_event_intel_cqm.c
---
 arch/x86/include/asm/intel_rdt.h           | 31 +++++++++++++++---------------
 arch/x86/include/asm/rdt_common.h          | 13 +++++++++++++
 arch/x86/kernel/cpu/intel_rdt.c            |  3 +++
 arch/x86/kernel/cpu/perf_event_intel_cqm.c | 20 +++++++------------
 4 files changed, 39 insertions(+), 28 deletions(-)
 create mode 100644 arch/x86/include/asm/rdt_common.h

diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
index 2fc496f..6aae109 100644
--- a/arch/x86/include/asm/intel_rdt.h
+++ b/arch/x86/include/asm/intel_rdt.h
@@ -4,12 +4,13 @@
 #ifdef CONFIG_CGROUP_RDT
 
 #include <linux/cgroup.h>
+#include <asm/rdt_common.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);
+
+DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
 extern struct static_key rdt_enable_key;
 
 struct rdt_subsys_info {
@@ -61,30 +62,30 @@ static inline struct intel_rdt *task_rdt(struct task_struct *task)
 static inline void rdt_sched_in(struct task_struct *task)
 {
 	struct intel_rdt *ir;
-	unsigned int clos;
+	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
+	unsigned long flags;
 
 	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);
-
+	raw_spin_lock_irqsave(&state->lock, flags);
 	rcu_read_lock();
 	ir = task_rdt(task);
-	if (ir->clos == clos) {
+	if (ir->clos == state->clos) {
 		rcu_read_unlock();
+		raw_spin_unlock_irqrestore(&state->lock, flags);
 		return;
 	}
 
-	wrmsr(MSR_IA32_PQR_ASSOC, 0, ir->clos);
-	this_cpu_write(x86_cpu_clos, ir->clos);
+	/*
+	 * PQR has closid in high 32 bits and CQM-RMID
+	 * in low 10 bits. Rewrite the exsting rmid from
+	 * software cache.
+	 */
+	wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, ir->clos);
+	state->clos = ir->clos;
 	rcu_read_unlock();
+	raw_spin_unlock_irqrestore(&state->lock, flags);
 }
 
 #else
diff --git a/arch/x86/include/asm/rdt_common.h b/arch/x86/include/asm/rdt_common.h
new file mode 100644
index 0000000..33fd8ea
--- /dev/null
+++ b/arch/x86/include/asm/rdt_common.h
@@ -0,0 +1,13 @@
+#ifndef _X86_RDT_H_
+#define _X86_RDT_H_
+
+#define MSR_IA32_PQR_ASSOC	0x0c8f
+
+struct intel_pqr_state {
+	raw_spinlock_t	lock;
+	int		rmid;
+	int		clos;
+	int		cnt;
+};
+
+#endif
diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 74b1e28..9da61b2 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -347,6 +347,9 @@ static inline bool rdt_update_cpumask(int cpu)
  */
 static inline void rdt_cpu_start(int cpu)
 {
+	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
+
+	state->clos = 0;
 	mutex_lock(&rdt_group_mutex);
 	if (rdt_update_cpumask(cpu))
 		cbm_update_msrs(cpu);
diff --git a/arch/x86/kernel/cpu/perf_event_intel_cqm.c b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
index e4d1b8b..fd039899 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_cqm.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_cqm.c
@@ -7,22 +7,16 @@
 #include <linux/perf_event.h>
 #include <linux/slab.h>
 #include <asm/cpu_device_id.h>
+#include <asm/rdt_common.h>
 #include "perf_event.h"
 
-#define MSR_IA32_PQR_ASSOC	0x0c8f
 #define MSR_IA32_QM_CTR		0x0c8e
 #define MSR_IA32_QM_EVTSEL	0x0c8d
 
 static unsigned int cqm_max_rmid = -1;
 static unsigned int cqm_l3_scale; /* supposedly cacheline size */
 
-struct intel_cqm_state {
-	raw_spinlock_t		lock;
-	int			rmid;
-	int			cnt;
-};
-
-static DEFINE_PER_CPU(struct intel_cqm_state, cqm_state);
+DEFINE_PER_CPU(struct intel_pqr_state, pqr_state);
 
 /*
  * Protects cache_cgroups and cqm_rmid_free_lru and cqm_rmid_limbo_lru.
@@ -961,7 +955,7 @@ out:
 
 static void intel_cqm_event_start(struct perf_event *event, int mode)
 {
-	struct intel_cqm_state *state = this_cpu_ptr(&cqm_state);
+	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
 	unsigned int rmid = event->hw.cqm_rmid;
 	unsigned long flags;
 
@@ -978,14 +972,14 @@ static void intel_cqm_event_start(struct perf_event *event, int mode)
 		WARN_ON_ONCE(state->rmid);
 
 	state->rmid = rmid;
-	wrmsrl(MSR_IA32_PQR_ASSOC, state->rmid);
+	wrmsr(MSR_IA32_PQR_ASSOC, state->rmid, state->clos);
 
 	raw_spin_unlock_irqrestore(&state->lock, flags);
 }
 
 static void intel_cqm_event_stop(struct perf_event *event, int mode)
 {
-	struct intel_cqm_state *state = this_cpu_ptr(&cqm_state);
+	struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
 	unsigned long flags;
 
 	if (event->hw.cqm_state & PERF_HES_STOPPED)
@@ -998,7 +992,7 @@ static void intel_cqm_event_stop(struct perf_event *event, int mode)
 
 	if (!--state->cnt) {
 		state->rmid = 0;
-		wrmsrl(MSR_IA32_PQR_ASSOC, 0);
+		wrmsr(MSR_IA32_PQR_ASSOC, 0, state->clos);
 	} else {
 		WARN_ON_ONCE(!state->rmid);
 	}
@@ -1243,7 +1237,7 @@ static inline void cqm_pick_event_reader(int cpu)
 
 static void intel_cqm_cpu_prepare(unsigned int cpu)
 {
-	struct intel_cqm_state *state = &per_cpu(cqm_state, cpu);
+	struct intel_pqr_state *state = &per_cpu(pqr_state, cpu);
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 
 	raw_spin_lock_init(&state->lock);
-- 
1.9.1

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