oprofile: Implement performance counter multiplexing

The number of hardware counters is limited. The multiplexing feature
enables OProfile to gather more events than counters are provided by
the hardware. This is realized by switching between events at an user
specified time interval.

A new file (/dev/oprofile/time_slice) is added for the user to specify
the timer interval in ms. If the number of events to profile is higher
than the number of hardware counters available, the patch will
schedule a work queue that switches the event counter and re-writes
the different sets of values into it. The switching mechanism needs to
be implemented for each architecture to support multiplexing. This
patch only implements AMD CPU support, but multiplexing can be easily
extended for other models and architectures.

There are follow-on patches that rework parts of this patch.

Signed-off-by: Jason Yeh <jason.yeh@amd.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>

1 files changed, 157 insertions, 5 deletions

diff --git a/arch/x86/oprofile/nmi_int.c b/arch/x86/oprofile/nmi_int.c
index fca8dc94531e..e54f6a0b35ac 100644
--- a/arch/x86/oprofile/nmi_int.c
+++ b/arch/x86/oprofile/nmi_int.c
@@ -1,11 +1,14 @@
 /**
  * @file nmi_int.c
  *
- * @remark Copyright 2002-2008 OProfile authors
+ * @remark Copyright 2002-2009 OProfile authors
  * @remark Read the file COPYING
  *
  * @author John Levon <levon@movementarian.org>
  * @author Robert Richter <robert.richter@amd.com>
+ * @author Barry Kasindorf <barry.kasindorf@amd.com>
+ * @author Jason Yeh <jason.yeh@amd.com>
+ * @author Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
  */
 
 #include <linux/init.h>
@@ -24,6 +27,12 @@
 #include "op_counter.h"
 #include "op_x86_model.h"
 
+
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+DEFINE_PER_CPU(int, switch_index);
+#endif
+
+
 static struct op_x86_model_spec const *model;
 static DEFINE_PER_CPU(struct op_msrs, cpu_msrs);
 static DEFINE_PER_CPU(unsigned long, saved_lvtpc);
@@ -31,6 +40,13 @@ static DEFINE_PER_CPU(unsigned long, saved_lvtpc);
 /* 0 == registered but off, 1 == registered and on */
 static int nmi_enabled = 0;
 
+
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+extern atomic_t multiplex_counter;
+#endif
+
+struct op_counter_config counter_config[OP_MAX_COUNTER];
+
 /* common functions */
 
 u64 op_x86_get_ctrl(struct op_x86_model_spec const *model,
@@ -95,6 +111,11 @@ static void free_msrs(void)
                 per_cpu(cpu_msrs, i).counters = NULL;
                 kfree(per_cpu(cpu_msrs, i).controls);
                 per_cpu(cpu_msrs, i).controls = NULL;
+
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+                kfree(per_cpu(cpu_msrs, i).multiplex);
+                per_cpu(cpu_msrs, i).multiplex = NULL;
+#endif
         }
 }
 
@@ -103,6 +124,9 @@ static int allocate_msrs(void)
         int success = 1;
         size_t controls_size = sizeof(struct op_msr) * model->num_controls;
         size_t counters_size = sizeof(struct op_msr) * model->num_counters;
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+        size_t multiplex_size = sizeof(struct op_msr) * model->num_virt_counters;
+#endif
 
         int i;
         for_each_possible_cpu(i) {
@@ -118,6 +142,14 @@ static int allocate_msrs(void)
                         success = 0;
                         break;
                 }
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+                per_cpu(cpu_msrs, i).multiplex =
+                                kmalloc(multiplex_size, GFP_KERNEL);
+                if (!per_cpu(cpu_msrs, i).multiplex) {
+                        success = 0;
+                        break;
+                }
+#endif
         }
 
         if (!success)
@@ -126,6 +158,25 @@ static int allocate_msrs(void)
         return success;
 }
 
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+
+static void nmi_setup_cpu_mux(struct op_msrs const * const msrs)
+{
+        int i;
+        struct op_msr *multiplex = msrs->multiplex;
+
+        for (i = 0; i < model->num_virt_counters; ++i) {
+                if (counter_config[i].enabled) {
+                        multiplex[i].saved = -(u64)counter_config[i].count;
+                } else {
+                        multiplex[i].addr  = 0;
+                        multiplex[i].saved = 0;
+                }
+        }
+}
+
+#endif
+
 static void nmi_cpu_setup(void *dummy)
 {
         int cpu = smp_processor_id();
@@ -133,6 +184,9 @@ static void nmi_cpu_setup(void *dummy)
         nmi_cpu_save_registers(msrs);
         spin_lock(&oprofilefs_lock);
         model->setup_ctrs(model, msrs);
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+        nmi_setup_cpu_mux(msrs);
+#endif
         spin_unlock(&oprofilefs_lock);
         per_cpu(saved_lvtpc, cpu) = apic_read(APIC_LVTPC);
         apic_write(APIC_LVTPC, APIC_DM_NMI);
@@ -173,14 +227,52 @@ static int nmi_setup(void)
                         memcpy(per_cpu(cpu_msrs, cpu).controls,
                                 per_cpu(cpu_msrs, 0).controls,
                                 sizeof(struct op_msr) * model->num_controls);
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+                        memcpy(per_cpu(cpu_msrs, cpu).multiplex,
+                                per_cpu(cpu_msrs, 0).multiplex,
+                                sizeof(struct op_msr) * model->num_virt_counters);
+#endif
                 }
-
         }
         on_each_cpu(nmi_cpu_setup, NULL, 1);
         nmi_enabled = 1;
         return 0;
 }
 
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+
+static void nmi_cpu_save_mpx_registers(struct op_msrs *msrs)
+{
+        unsigned int si = __get_cpu_var(switch_index);
+        struct op_msr *multiplex = msrs->multiplex;
+        unsigned int i;
+
+        for (i = 0; i < model->num_counters; ++i) {
+                int offset = i + si;
+                if (multiplex[offset].addr) {
+                        rdmsrl(multiplex[offset].addr,
+                               multiplex[offset].saved);
+                }
+        }
+}
+
+static void nmi_cpu_restore_mpx_registers(struct op_msrs *msrs)
+{
+        unsigned int si = __get_cpu_var(switch_index);
+        struct op_msr *multiplex = msrs->multiplex;
+        unsigned int i;
+
+        for (i = 0; i < model->num_counters; ++i) {
+                int offset = i + si;
+                if (multiplex[offset].addr) {
+                        wrmsrl(multiplex[offset].addr,
+                               multiplex[offset].saved);
+                }
+        }
+}
+
+#endif
+
 static void nmi_cpu_restore_registers(struct op_msrs *msrs)
 {
         struct op_msr *counters = msrs->counters;
@@ -214,6 +306,9 @@ static void nmi_cpu_shutdown(void *dummy)
         apic_write(APIC_LVTPC, per_cpu(saved_lvtpc, cpu));
         apic_write(APIC_LVTERR, v);
         nmi_cpu_restore_registers(msrs);
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+        __get_cpu_var(switch_index) = 0;
+#endif
 }
 
 static void nmi_shutdown(void)
@@ -252,16 +347,15 @@ static void nmi_stop(void)
         on_each_cpu(nmi_cpu_stop, NULL, 1);
 }
 
-struct op_counter_config counter_config[OP_MAX_COUNTER];
-
 static int nmi_create_files(struct super_block *sb, struct dentry *root)
 {
         unsigned int i;
 
-        for (i = 0; i < model->num_counters; ++i) {
+        for (i = 0; i < model->num_virt_counters; ++i) {
                 struct dentry *dir;
                 char buf[4];
 
+#ifndef CONFIG_OPROFILE_EVENT_MULTIPLEX
                 /* quick little hack to _not_ expose a counter if it is not
                  * available for use.  This should protect userspace app.
                  * NOTE:  assumes 1:1 mapping here (that counters are organized
@@ -269,6 +363,7 @@ static int nmi_create_files(struct super_block *sb, struct dentry *root)
                  */
                 if (unlikely(!avail_to_resrv_perfctr_nmi_bit(i)))
                         continue;
+#endif /* CONFIG_OPROFILE_EVENT_MULTIPLEX */
 
                 snprintf(buf,  sizeof(buf), "%d", i);
                 dir = oprofilefs_mkdir(sb, root, buf);
@@ -283,6 +378,57 @@ static int nmi_create_files(struct super_block *sb, struct dentry *root)
         return 0;
 }
 
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+
+static void nmi_cpu_switch(void *dummy)
+{
+        int cpu = smp_processor_id();
+        int si = per_cpu(switch_index, cpu);
+        struct op_msrs *msrs = &per_cpu(cpu_msrs, cpu);
+
+        nmi_cpu_stop(NULL);
+        nmi_cpu_save_mpx_registers(msrs);
+
+        /* move to next set */
+        si += model->num_counters;
+        if ((si > model->num_virt_counters) || (counter_config[si].count == 0))
+                per_cpu(switch_index, cpu) = 0;
+        else
+                per_cpu(switch_index, cpu) = si;
+
+        model->switch_ctrl(model, msrs);
+        nmi_cpu_restore_mpx_registers(msrs);
+
+        nmi_cpu_start(NULL);
+}
+
+
+/*
+ * Quick check to see if multiplexing is necessary.
+ * The check should be sufficient since counters are used
+ * in ordre.
+ */
+static int nmi_multiplex_on(void)
+{
+        return counter_config[model->num_counters].count ? 0 : -EINVAL;
+}
+
+static int nmi_switch_event(void)
+{
+        if (!model->switch_ctrl)
+                return -ENOSYS;         /* not implemented */
+        if (nmi_multiplex_on() < 0)
+                return -EINVAL;         /* not necessary */
+
+        on_each_cpu(nmi_cpu_switch, NULL, 1);
+
+        atomic_inc(&multiplex_counter);
+
+        return 0;
+}
+
+#endif
+
 #ifdef CONFIG_SMP
 static int oprofile_cpu_notifier(struct notifier_block *b, unsigned long action,
                                  void *data)
@@ -516,12 +662,18 @@ int __init op_nmi_init(struct oprofile_operations *ops)
         register_cpu_notifier(&oprofile_cpu_nb);
 #endif
         /* default values, can be overwritten by model */
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+        __raw_get_cpu_var(switch_index) = 0;
+#endif
         ops->create_files       = nmi_create_files;
         ops->setup              = nmi_setup;
         ops->shutdown           = nmi_shutdown;
         ops->start              = nmi_start;
         ops->stop               = nmi_stop;
         ops->cpu_type           = cpu_type;
+#ifdef CONFIG_OPROFILE_EVENT_MULTIPLEX
+        ops->switch_events      = nmi_switch_event;
+#endif
 
         if (model->init)
                 ret = model->init(ops);