tracing: remove on the fly allocator from function profiler
Impact: safer code
| From: Steven Rostedt <srostedt@xxxxxxxxxx>
|
| Impact: safer code
|
| The on the fly allocator for the function profiler was to save
| memory. But at the expense of stability. Although it survived several
| tests, allocating from the function tracer is just too risky, just
| to save space.
|
| This patch removes the allocator and simply allocates enough entries
| at start up.
|
| Each function gets a profiling structure of 40 bytes. With an average
| of 20K functions, and this is for each CPU, we have 800K per online
| CPU. This is not too bad, at least for non-embedded.
|
| Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@xxxxxxxxxx>
---
kernel/trace/ftrace.c | 76 +++++++++++++++++++++++++++---------------------
1 files changed, 43 insertions(+), 33 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a141d84..4d90c91 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -399,6 +399,8 @@ static void ftrace_profile_reset(struct ftrace_profile_stat *stat)
int ftrace_profile_pages_init(struct ftrace_profile_stat *stat)
{
struct ftrace_profile_page *pg;
+ int functions;
+ int pages;
int i;
/* If we already allocated, do nothing */
@@ -409,22 +411,46 @@ int ftrace_profile_pages_init(struct ftrace_profile_stat *stat)
if (!stat->pages)
return -ENOMEM;
+#ifdef CONFIG_DYNAMIC_FTRACE
+ functions = ftrace_update_tot_cnt;
+#else
+ /*
+ * We do not know the number of functions that exist because
+ * dynamic tracing is what counts them. With past experience
+ * we have around 20K functions. That should be more than enough.
+ * It is highly unlikely we will execute every function in
+ * the kernel.
+ */
+ functions = 20000;
+#endif
+
pg = stat->start = stat->pages;
- /* allocate 10 more pages to start */
- for (i = 0; i < 10; i++) {
+ pages = DIV_ROUND_UP(functions, PROFILES_PER_PAGE);
+
+ for (i = 0; i < pages; i++) {
pg->next = (void *)get_zeroed_page(GFP_KERNEL);
- /*
- * We only care about allocating profile_pages, if
- * we failed to allocate here, hopefully we will allocate
- * later.
- */
if (!pg->next)
- break;
+ goto out_free;
pg = pg->next;
}
return 0;
+
+ out_free:
+ pg = stat->start;
+ while (pg) {
+ unsigned long tmp = (unsigned long)pg;
+
+ pg = pg->next;
+ free_page(tmp);
+ }
+
+ free_page((unsigned long)stat->pages);
+ stat->pages = NULL;
+ stat->start = NULL;
+
+ return -ENOMEM;
}
static int ftrace_profile_init_cpu(int cpu)
@@ -458,7 +484,7 @@ static int ftrace_profile_init_cpu(int cpu)
ftrace_profile_bits++;
}
- /* Preallocate a few pages */
+ /* Preallocate the function profiling pages */
if (ftrace_profile_pages_init(stat) < 0) {
kfree(stat->hash);
stat->hash = NULL;
@@ -514,24 +540,21 @@ static void ftrace_add_profile(struct ftrace_profile_stat *stat,
hlist_add_head_rcu(&rec->node, &stat->hash[key]);
}
-/* Interrupts must be disabled calling this */
+/*
+ * The memory is already allocated, this simply finds a new record to use.
+ */
static struct ftrace_profile *
-ftrace_profile_alloc(struct ftrace_profile_stat *stat,
- unsigned long ip, bool alloc_safe)
+ftrace_profile_alloc(struct ftrace_profile_stat *stat, unsigned long ip)
{
struct ftrace_profile *rec = NULL;
- /* prevent recursion */
+ /* prevent recursion (from NMIs) */
if (atomic_inc_return(&stat->disabled) != 1)
goto out;
- /* Try to always keep another page available */
- 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
+ * Try to find the function again since an NMI
+ * could have added it
*/
rec = ftrace_find_profiled_func(stat, ip);
if (rec)
@@ -553,29 +576,16 @@ ftrace_profile_alloc(struct ftrace_profile_stat *stat,
return rec;
}
-/*
- * If we are not in an interrupt, or softirq and
- * and interrupts are disabled and preemption is not enabled
- * (not in a spinlock) then it should be safe to allocate memory.
- */
-static bool ftrace_safe_to_allocate(void)
-{
- return !in_interrupt() && irqs_disabled() && !preempt_count();
-}
-
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;
if (!ftrace_profile_enabled)
return;
- alloc_safe = ftrace_safe_to_allocate();
-
local_irq_save(flags);
stat = &__get_cpu_var(ftrace_profile_stats);
@@ -584,7 +594,7 @@ function_profile_call(unsigned long ip, unsigned long parent_ip)
rec = ftrace_find_profiled_func(stat, ip);
if (!rec) {
- rec = ftrace_profile_alloc(stat, ip, alloc_safe);
+ rec = ftrace_profile_alloc(stat, ip);
if (!rec)
goto out;
}
--
1.6.2
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