tracing: make the function profiler per cpu

Impact: speed enhancement

By making the function profiler record in per cpu data we not only
get better readings, avoid races, we also do not have to take any
locks.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 130 insertions, 69 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a9ccd71fc922..ed1fc5021d44 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -257,28 +257,28 @@ struct ftrace_profile_page {
         struct ftrace_profile           records[];
 };
 
+struct ftrace_profile_stat {
+        atomic_t                        disabled;
+        struct hlist_head               *hash;
+        struct ftrace_profile_page      *pages;
+        struct ftrace_profile_page      *start;
+        struct tracer_stat              stat;
+};
+
 #define PROFILE_RECORDS_SIZE                                            \
         (PAGE_SIZE - offsetof(struct ftrace_profile_page, records))
 
 #define PROFILES_PER_PAGE                                       \
         (PROFILE_RECORDS_SIZE / sizeof(struct ftrace_profile))
 
-/* TODO: make these percpu, to prevent cache line bouncing */
-static struct ftrace_profile_page *profile_pages_start;
-static struct ftrace_profile_page *profile_pages;
-
-static struct hlist_head *ftrace_profile_hash;
 static int ftrace_profile_bits;
 static int ftrace_profile_enabled;
 static DEFINE_MUTEX(ftrace_profile_lock);
 
-static DEFINE_PER_CPU(atomic_t, ftrace_profile_disable);
+static DEFINE_PER_CPU(struct ftrace_profile_stat, ftrace_profile_stats);
 
 #define FTRACE_PROFILE_HASH_SIZE 1024 /* must be power of 2 */
 
-static raw_spinlock_t ftrace_profile_rec_lock =
-        (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
-
 static void *
 function_stat_next(void *v, int idx)
 {
@@ -303,7 +303,13 @@ function_stat_next(void *v, int idx)
 
 static void *function_stat_start(struct tracer_stat *trace)
 {
-        return function_stat_next(&profile_pages_start->records[0], 0);
+        struct ftrace_profile_stat *stat =
+                container_of(trace, struct ftrace_profile_stat, stat);
+
+        if (!stat || !stat->start)
+                return NULL;
+
+        return function_stat_next(&stat->start->records[0], 0);
 }
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -374,20 +380,11 @@ static int function_stat_show(struct seq_file *m, void *v)
         return 0;
 }
 
-static struct tracer_stat function_stats = {
-        .name = "functions",
-        .stat_start = function_stat_start,
-        .stat_next = function_stat_next,
-        .stat_cmp = function_stat_cmp,
-        .stat_headers = function_stat_headers,
-        .stat_show = function_stat_show
-};
-
-static void ftrace_profile_reset(void)
+static void ftrace_profile_reset(struct ftrace_profile_stat *stat)
 {
         struct ftrace_profile_page *pg;
 
-        pg = profile_pages = profile_pages_start;
+        pg = stat->pages = stat->start;
 
         while (pg) {
                 memset(pg->records, 0, PROFILE_RECORDS_SIZE);
@@ -395,24 +392,24 @@ static void ftrace_profile_reset(void)
                 pg = pg->next;
         }
 
-        memset(ftrace_profile_hash, 0,
+        memset(stat->hash, 0,
                FTRACE_PROFILE_HASH_SIZE * sizeof(struct hlist_head));
 }
 
-int ftrace_profile_pages_init(void)
+int ftrace_profile_pages_init(struct ftrace_profile_stat *stat)
 {
         struct ftrace_profile_page *pg;
         int i;
 
         /* If we already allocated, do nothing */
-        if (profile_pages)
+        if (stat->pages)
                 return 0;
 
-        profile_pages = (void *)get_zeroed_page(GFP_KERNEL);
-        if (!profile_pages)
+        stat->pages = (void *)get_zeroed_page(GFP_KERNEL);
+        if (!stat->pages)
                 return -ENOMEM;
 
-        pg = profile_pages_start = profile_pages;
+        pg = stat->start = stat->pages;
 
         /* allocate 10 more pages to start */
         for (i = 0; i < 10; i++) {
@@ -430,13 +427,16 @@ int ftrace_profile_pages_init(void)
         return 0;
 }
 
-static int ftrace_profile_init(void)
+static int ftrace_profile_init_cpu(int cpu)
 {
+        struct ftrace_profile_stat *stat;
         int size;
 
-        if (ftrace_profile_hash) {
+        stat = &per_cpu(ftrace_profile_stats, cpu);
+
+        if (stat->hash) {
                 /* If the profile is already created, simply reset it */
-                ftrace_profile_reset();
+                ftrace_profile_reset(stat);
                 return 0;
         }
 
@@ -446,29 +446,45 @@ static int ftrace_profile_init(void)
          */
         size = FTRACE_PROFILE_HASH_SIZE;
 
-        ftrace_profile_hash =
-                kzalloc(sizeof(struct hlist_head) * size, GFP_KERNEL);
+        stat->hash = kzalloc(sizeof(struct hlist_head) * size, GFP_KERNEL);
 
-        if (!ftrace_profile_hash)
+        if (!stat->hash)
                 return -ENOMEM;
 
-        size--;
+        if (!ftrace_profile_bits) {
+                size--;
 
-        for (; size; size >>= 1)
-                ftrace_profile_bits++;
+                for (; size; size >>= 1)
+                        ftrace_profile_bits++;
+        }
 
         /* Preallocate a few pages */
-        if (ftrace_profile_pages_init() < 0) {
-                kfree(ftrace_profile_hash);
-                ftrace_profile_hash = NULL;
+        if (ftrace_profile_pages_init(stat) < 0) {
+                kfree(stat->hash);
+                stat->hash = NULL;
                 return -ENOMEM;
         }
 
         return 0;
 }
 
+static int ftrace_profile_init(void)
+{
+        int cpu;
+        int ret = 0;
+
+        for_each_online_cpu(cpu) {
+                ret = ftrace_profile_init_cpu(cpu);
+                if (ret)
+                        break;
+        }
+
+        return ret;
+}
+
 /* interrupts must be disabled */
-static struct ftrace_profile *ftrace_find_profiled_func(unsigned long ip)
+static struct ftrace_profile *
+ftrace_find_profiled_func(struct ftrace_profile_stat *stat, unsigned long ip)
 {
         struct ftrace_profile *rec;
         struct hlist_head *hhd;
@@ -476,7 +492,7 @@ static struct ftrace_profile *ftrace_find_profiled_func(unsigned long ip)
         unsigned long key;
 
         key = hash_long(ip, ftrace_profile_bits);
-        hhd = &ftrace_profile_hash[key];
+        hhd = &stat->hash[key];
 
         if (hlist_empty(hhd))
                 return NULL;
@@ -489,52 +505,50 @@ static struct ftrace_profile *ftrace_find_profiled_func(unsigned long ip)
         return NULL;
 }
 
-static void ftrace_add_profile(struct ftrace_profile *rec)
+static void ftrace_add_profile(struct ftrace_profile_stat *stat,
+                               struct ftrace_profile *rec)
 {
         unsigned long key;
 
         key = hash_long(rec->ip, ftrace_profile_bits);
-        hlist_add_head_rcu(&rec->node, &ftrace_profile_hash[key]);
+        hlist_add_head_rcu(&rec->node, &stat->hash[key]);
 }
 
 /* Interrupts must be disabled calling this */
 static struct ftrace_profile *
-ftrace_profile_alloc(unsigned long ip, bool alloc_safe)
+ftrace_profile_alloc(struct ftrace_profile_stat *stat,
+                     unsigned long ip, bool alloc_safe)
 {
         struct ftrace_profile *rec = NULL;
 
         /* prevent recursion */
-        if (atomic_inc_return(&__get_cpu_var(ftrace_profile_disable)) != 1)
+        if (atomic_inc_return(&stat->disabled) != 1)
                 goto out;
 
-        __raw_spin_lock(&ftrace_profile_rec_lock);
-
         /* Try to always keep another page available */
-        if (!profile_pages->next && alloc_safe)
-                profile_pages->next = (void *)get_zeroed_page(GFP_ATOMIC);
+        if (!stat->pages->next && alloc_safe)
+                stat->pages->next = (void *)get_zeroed_page(GFP_ATOMIC);
 
         /*
          * Try to find the function again since another
          * task on another CPU could have added it
          */
-        rec = ftrace_find_profiled_func(ip);
+        rec = ftrace_find_profiled_func(stat, ip);
         if (rec)
-                goto out_unlock;
+                goto out;
 
-        if (profile_pages->index == PROFILES_PER_PAGE) {
-                if (!profile_pages->next)
-                        goto out_unlock;
-                profile_pages = profile_pages->next;
+        if (stat->pages->index == PROFILES_PER_PAGE) {
+                if (!stat->pages->next)
+                        goto out;
+                stat->pages = stat->pages->next;
         }
 
-        rec = &profile_pages->records[profile_pages->index++];
+        rec = &stat->pages->records[stat->pages->index++];
         rec->ip = ip;
-        ftrace_add_profile(rec);
+        ftrace_add_profile(stat, rec);
 
- out_unlock:
-        __raw_spin_unlock(&ftrace_profile_rec_lock);
  out:
-        atomic_dec(&__get_cpu_var(ftrace_profile_disable));
+        atomic_dec(&stat->disabled);
 
         return rec;
 }
@@ -552,6 +566,7 @@ static bool ftrace_safe_to_allocate(void)
 static void
 function_profile_call(unsigned long ip, unsigned long parent_ip)
 {
+        struct ftrace_profile_stat *stat;
         struct ftrace_profile *rec;
         unsigned long flags;
         bool alloc_safe;
@@ -562,9 +577,14 @@ function_profile_call(unsigned long ip, unsigned long parent_ip)
         alloc_safe = ftrace_safe_to_allocate();
 
         local_irq_save(flags);
-        rec = ftrace_find_profiled_func(ip);
+
+        stat = &__get_cpu_var(ftrace_profile_stats);
+        if (!stat->hash)
+                goto out;
+
+        rec = ftrace_find_profiled_func(stat, ip);
         if (!rec) {
-                rec = ftrace_profile_alloc(ip, alloc_safe);
+                rec = ftrace_profile_alloc(stat, ip, alloc_safe);
                 if (!rec)
                         goto out;
         }
@@ -583,13 +603,19 @@ static int profile_graph_entry(struct ftrace_graph_ent *trace)
 
 static void profile_graph_return(struct ftrace_graph_ret *trace)
 {
-        unsigned long flags;
+        struct ftrace_profile_stat *stat;
         struct ftrace_profile *rec;
+        unsigned long flags;
 
         local_irq_save(flags);
-        rec = ftrace_find_profiled_func(trace->func);
+        stat = &__get_cpu_var(ftrace_profile_stats);
+        if (!stat->hash)
+                goto out;
+
+        rec = ftrace_find_profiled_func(stat, trace->func);
         if (rec)
                 rec->time += trace->rettime - trace->calltime;
+ out:
         local_irq_restore(flags);
 }
 
@@ -687,16 +713,51 @@ static const struct file_operations ftrace_profile_fops = {
         .write          = ftrace_profile_write,
 };
 
+/* used to initialize the real stat files */
+static struct tracer_stat function_stats __initdata = {
+        .name = "functions",
+        .stat_start = function_stat_start,
+        .stat_next = function_stat_next,
+        .stat_cmp = function_stat_cmp,
+        .stat_headers = function_stat_headers,
+        .stat_show = function_stat_show
+};
+
 static void ftrace_profile_debugfs(struct dentry *d_tracer)
 {
+        struct ftrace_profile_stat *stat;
         struct dentry *entry;
+        char *name;
         int ret;
+        int cpu;
 
-        ret = register_stat_tracer(&function_stats);
-        if (ret) {
-                pr_warning("Warning: could not register "
-                           "function stats\n");
-                return;
+        for_each_possible_cpu(cpu) {
+                stat = &per_cpu(ftrace_profile_stats, cpu);
+
+                /* allocate enough for function name + cpu number */
+                name = kmalloc(32, GFP_KERNEL);
+                if (!name) {
+                        /*
+                         * The files created are permanent, if something happens
+                         * we still do not free memory.
+                         */
+                        kfree(stat);
+                        WARN(1,
+                             "Could not allocate stat file for cpu %d\n",
+                             cpu);
+                        return;
+                }
+                stat->stat = function_stats;
+                snprintf(name, 32, "function%d", cpu);
+                stat->stat.name = name;
+                ret = register_stat_tracer(&stat->stat);
+                if (ret) {
+                        WARN(1,
+                             "Could not register function stat for cpu %d\n",
+                             cpu);
+                        kfree(name);
+                        return;
+                }
         }
 
         entry = debugfs_create_file("function_profile_enabled", 0644,