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ftrace: trace_entries to dynamically change trace buffer size 

This patch adds /debug/tracing/trace_entries that allows users to
see as well as modify the number of trace entries the buffers hold.

The number of entries only increments in ENTRIES_PER_PAGE which is
calculated by the size of an entry with the number of entries that
can fit in a page. The user does not need to use an exact size, but
the entries will be rounded to one of the increments.

Trying to set the entries to 0 will return with -EINVAL.

To avoid race conditions, the modification of the buffer size can only
be done when tracing is completely disabled (current_tracer == none).
A info message will be printed if a user tries to modify the buffer size
when not set to none.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Steven Rostedt 2008-05-12 21:20:59 +02:00 committed by Thomas Gleixner
parent 05bd68c514
commit a98a3c3fde
1 changed files with 137 additions and 8 deletions
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145
kernel/trace/trace.c
View File

@ -35,6 +35,15 @@
unsigned long __read_mostly tracing_max_latency = (cycle_t)ULONG_MAX;
unsigned long __read_mostly tracing_thresh;
/* dummy trace to disable tracing */
static struct tracer no_tracer __read_mostly =
{
.name = "none",
};
static int trace_alloc_page(void);
static int trace_free_page(void);
static int tracing_disabled = 1;
long
@ -2364,6 +2373,70 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
return read;
}
static ssize_t
tracing_entries_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
{
struct trace_array *tr = filp->private_data;
char buf[64];
int r;
r = sprintf(buf, "%lu\n", tr->entries);
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}
static ssize_t
tracing_entries_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
unsigned long val;
char buf[64];
if (cnt > 63)
cnt = 63;
if (copy_from_user(&buf, ubuf, cnt))
return -EFAULT;
buf[cnt] = 0;
val = simple_strtoul(buf, NULL, 10);
/* must have at least 1 entry */
if (!val)
return -EINVAL;
mutex_lock(&trace_types_lock);
if (current_trace != &no_tracer) {
cnt = -EBUSY;
pr_info("ftrace: set current_tracer to none"
" before modifying buffer size\n");
goto out;
}
if (val > global_trace.entries) {
while (global_trace.entries < val) {
if (trace_alloc_page()) {
cnt = -ENOMEM;
goto out;
}
}
} else {
/* include the number of entries in val (inc of page entries) */
while (global_trace.entries > val + (ENTRIES_PER_PAGE - 1))
trace_free_page();
}
filp->f_pos += cnt;
out:
max_tr.entries = global_trace.entries;
mutex_unlock(&trace_types_lock);
return cnt;
}
static struct file_operations tracing_max_lat_fops = {
.open = tracing_open_generic,
.read = tracing_max_lat_read,
@ -2389,6 +2462,12 @@ static struct file_operations tracing_pipe_fops = {
.release = tracing_release_pipe,
};
static struct file_operations tracing_entries_fops = {
.open = tracing_open_generic,
.read = tracing_entries_read,
.write = tracing_entries_write,
};
#ifdef CONFIG_DYNAMIC_FTRACE
static ssize_t
@ -2500,6 +2579,12 @@ static __init void tracer_init_debugfs(void)
pr_warning("Could not create debugfs "
"'tracing_threash' entry\n");
entry = debugfs_create_file("trace_entries", 0644, d_tracer,
&global_trace, &tracing_entries_fops);
if (!entry)
pr_warning("Could not create debugfs "
"'tracing_threash' entry\n");
#ifdef CONFIG_DYNAMIC_FTRACE
entry = debugfs_create_file("dyn_ftrace_total_info", 0444, d_tracer,
&ftrace_update_tot_cnt,
@ -2510,12 +2595,6 @@ static __init void tracer_init_debugfs(void)
#endif
}
/* dummy trace to disable tracing */
static struct tracer no_tracer __read_mostly =
{
.name = "none",
};
static int trace_alloc_page(void)
{
struct trace_array_cpu *data;
@ -2552,7 +2631,6 @@ static int trace_alloc_page(void)
/* Now that we successfully allocate a page per CPU, add them */
for_each_possible_cpu(i) {
data = global_trace.data[i];
data->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
page = list_entry(pages.next, struct page, lru);
list_del_init(&page->lru);
list_add_tail(&page->lru, &data->trace_pages);
@ -2560,7 +2638,6 @@ static int trace_alloc_page(void)
#ifdef CONFIG_TRACER_MAX_TRACE
data = max_tr.data[i];
data->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
page = list_entry(pages.next, struct page, lru);
list_del_init(&page->lru);
list_add_tail(&page->lru, &data->trace_pages);
@ -2579,6 +2656,55 @@ static int trace_alloc_page(void)
return -ENOMEM;
}
static int trace_free_page(void)
{
struct trace_array_cpu *data;
struct page *page;
struct list_head *p;
int i;
int ret = 0;
/* free one page from each buffer */
for_each_possible_cpu(i) {
data = global_trace.data[i];
p = data->trace_pages.next;
if (p == &data->trace_pages) {
/* should never happen */
WARN_ON(1);
tracing_disabled = 1;
ret = -1;
break;
}
page = list_entry(p, struct page, lru);
ClearPageLRU(page);
list_del(&page->lru);
__free_page(page);
tracing_reset(data);
#ifdef CONFIG_TRACER_MAX_TRACE
data = max_tr.data[i];
p = data->trace_pages.next;
if (p == &data->trace_pages) {
/* should never happen */
WARN_ON(1);
tracing_disabled = 1;
ret = -1;
break;
}
page = list_entry(p, struct page, lru);
ClearPageLRU(page);
list_del(&page->lru);
__free_page(page);
tracing_reset(data);
#endif
}
global_trace.entries -= ENTRIES_PER_PAGE;
return ret;
}
__init static int tracer_alloc_buffers(void)
{
struct trace_array_cpu *data;
@ -2609,6 +2735,9 @@ __init static int tracer_alloc_buffers(void)
/* use the LRU flag to differentiate the two buffers */
ClearPageLRU(page);
data->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
max_tr.data[i]->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
/* Only allocate if we are actually using the max trace */
#ifdef CONFIG_TRACER_MAX_TRACE
array = (void *)__get_free_page(GFP_KERNEL);