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tracing: make the function profiler per cpu
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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>
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Steven Rostedt committed Mar 25, 2009
1 parent 0706f1c commit cafb168
Showing 1 changed file with 130 additions and 69 deletions.
199 changes: 130 additions & 69 deletions kernel/trace/ftrace.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
{
Expand All @@ -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
Expand Down Expand Up @@ -374,45 +380,36 @@ 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);
pg->index = 0;
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++) {
Expand All @@ -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;
}

Expand All @@ -446,37 +446,53 @@ 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;
struct hlist_node *n;
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;
Expand All @@ -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;
}
Expand All @@ -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;
Expand All @@ -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;
}
Expand All @@ -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);
}

Expand Down Expand Up @@ -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,
Expand Down

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