Re: [PATCH 1/5][RFC] tracing: add function profiler

Frederic Weisbecker
2009-03-25T19:12:14Z

On Tue, Mar 24, 2009 at 11:56:47PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> Impact: new profiling feature
>
> This patch adds a function profiler. In debugfs/tracing/ two new
> files are created.
>
> function_profile_enabled - to enable or disable profiling
>
> trace_stat/functions - the profiled functions.
>
> For example:
>
> echo 1 > /debugfs/tracing/function_profile_enabled
> ./hackbench 50
> echo 0 > /debugfs/tracing/function_profile_enabled
>
> yields:
>
> cat /debugfs/tracing/trace_stat/functions
>
> Function Hit
> -------- ---
> _spin_lock 10106442
> _spin_unlock 10097492
> kfree 6013704
> _spin_unlock_irqrestore 4423941
> _spin_lock_irqsave 4406825
> __phys_addr 4181686
> __slab_free 4038222
> dput 4030130
> path_put 4023387
> unroll_tree_refs 4019532
> [...]
>
> The most hit functions are listed first. Functions that are not
> hit are not listed.
>
> This feature depends on and uses dynamic function tracing. When the
> function profiling is disabled, no overhead occurs. But it still
> takes up around 300KB to hold the data, thus it is not recomended
> to keep it enabled for systems low on memory.
>
> When a '1' is echoed into the function_profile_enabled file, the
> counters for is function is reset back to zero. Thus you can see what
> functions are hit most by different programs.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> include/linux/ftrace.h | 4 +
> kernel/trace/Kconfig | 19 +++
> kernel/trace/ftrace.c | 313 +++++++++++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 334 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 015a3d2..0456c3a 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -153,6 +153,10 @@ struct dyn_ftrace {
> unsigned long flags;
> struct dyn_ftrace *newlist;
> };
> +#ifdef CONFIG_FUNCTION_PROFILER
> + unsigned long counter;
> + struct hlist_node node;
> +#endif
> struct dyn_arch_ftrace arch;
> };
>
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 8a4d729..95e9ad5 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -105,6 +105,7 @@ config FUNCTION_GRAPH_TRACER
> This is done by setting the current return address on the current
> task structure into a stack of calls.
>
> +
> config IRQSOFF_TRACER
> bool "Interrupts-off Latency Tracer"
> default n
> @@ -376,6 +377,24 @@ config DYNAMIC_FTRACE
> were made. If so, it runs stop_machine (stops all CPUS)
> and modifies the code to jump over the call to ftrace.
>
> +config FUNCTION_PROFILER
> + bool "Kernel function profiler"
> + depends on DYNAMIC_FTRACE
> + default n
> + help
> + This option enables the kernel function profiler. When the dynamic
> + function tracing is enabled, a counter is added into the function
> + records used by the dynamic function tracer. A file is created in
> + debugfs called function_profile_enabled which defaults to zero.
> + When a 1 is echoed into this file profiling begins, and when a
> + zero is entered, profiling stops. A file in the trace_stats
> + directory called functions, that show the list of functions that
> + have been hit and their counters.
> +
> + This takes up around 320K more memory.
> +
> + If in doubt, say N
> +
> config FTRACE_MCOUNT_RECORD
> def_bool y
> depends on DYNAMIC_FTRACE
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 7b8722b..11f364c 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -34,6 +34,7 @@
> #include <asm/ftrace.h>
>
> #include "trace.h"
> +#include "trace_stat.h"
>
> #define FTRACE_WARN_ON(cond) \
> do { \
> @@ -261,7 +262,6 @@ struct ftrace_func_probe {
> struct rcu_head rcu;
> };
>
> -
> enum {
> FTRACE_ENABLE_CALLS = (1 << 0),
> FTRACE_DISABLE_CALLS = (1 << 1),
> @@ -309,6 +309,307 @@ static struct dyn_ftrace *ftrace_free_records;
> } \
> }
>
> +#ifdef CONFIG_FUNCTION_PROFILER
> +static struct hlist_head *ftrace_profile_hash;
> +static int ftrace_profile_bits;
> +static int ftrace_profile_enabled;
> +static DEFINE_MUTEX(ftrace_profile_lock);
> +
> +static void *
> +function_stat_next(void *v, int idx)
> +{
> + struct dyn_ftrace *rec = v;
> + struct ftrace_page *pg;
> +
> + pg = (struct ftrace_page *)((unsigned long)rec & PAGE_MASK);
> +
> + again:
> + rec++;
> + if ((void *)rec >= (void *)&pg->records[pg->index]) {
> + pg = pg->next;
> + if (!pg)
> + return NULL;
> + rec = &pg->records[0];
> + }
> +
> + if (rec->flags & FTRACE_FL_FREE ||
> + rec->flags & FTRACE_FL_FAILED ||
> + !(rec->flags & FTRACE_FL_CONVERTED) ||
> + /* ignore non hit functions */
> + !rec->counter)
> + goto again;
> +
> + return rec;
> +}
> +
> +static void *function_stat_start(struct tracer_stat *trace)
> +{
> + return function_stat_next(&ftrace_pages_start->records[0], 0);
> +}
> +
> +static int function_stat_cmp(void *p1, void *p2)
> +{
> + struct dyn_ftrace *a = p1;
> + struct dyn_ftrace *b = p2;
> +
> + if (a->counter < b->counter)
> + return -1;
> + if (a->counter > b->counter)
> + return 1;
> + else
> + return 0;
> +}
> +
> +static int function_stat_headers(struct seq_file *m)
> +{
> + seq_printf(m, " Function Hit\n"
> + " -------- ---\n");
> + return 0;
> +}
> +
> +static int function_stat_show(struct seq_file *m, void *v)
> +{
> + struct dyn_ftrace *rec = v;
> + char str[KSYM_SYMBOL_LEN];
> +
> + kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> +
> + seq_printf(m, " %-30.30s %10lu\n", str, rec->counter);
> + 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_init(int nr_funcs)
> +{
> + unsigned long addr;
> + int order;
> + int size;
> +
> + /*
> + * We are profiling all functions, lets make it 1/4th of the
> + * number of functions that are in core kernel. So we have to
> + * iterate 4 times.
> + */
> + order = (sizeof(struct hlist_head) * nr_funcs) / 4;
> + order = get_order(order);
> + size = 1 << (PAGE_SHIFT + order);
> +
> + pr_info("Allocating %d KB for profiler hash\n", size >> 10);
> +
> + addr = __get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
> + if (!addr) {
> + pr_warning("Could not allocate function profiler hash\n");
> + return;
> + }
> +
> + ftrace_profile_hash = (void *)addr;
> +
> + /*
> + * struct hlist_head should be a pointer of 4 or 8 bytes.
> + * And a simple bit manipulation can be done, but if for
> + * some reason struct hlist_head is not a mulitple of 2,
> + * then we play it safe, and simply count. This function
> + * is done once at boot up, so it is not that critical in
> + * performance.
> + */
> +
> + size--;
> + size /= sizeof(struct hlist_head);
> +
> + for (; size; size >>= 1)
> + ftrace_profile_bits++;
> +
> + pr_info("Function profiler has %d hash buckets\n",
> + 1 << ftrace_profile_bits);
> +
> + return;
> +}
> +
> +static ssize_t
> +ftrace_profile_read(struct file *filp, char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + char buf[64];
> + int r;
> +
> + r = sprintf(buf, "%u\n", ftrace_profile_enabled);
> + return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> +}
> +
> +static void ftrace_profile_reset(void)
> +{
> + struct dyn_ftrace *rec;
> + struct ftrace_page *pg;
> +
> + do_for_each_ftrace_rec(pg, rec) {
> + rec->counter = 0;
> + } while_for_each_ftrace_rec();
> +}
> +
> +static struct dyn_ftrace *ftrace_find_profiled_func(unsigned long ip)
> +{
> + struct dyn_ftrace *rec;
> + struct hlist_head *hhd;
> + struct hlist_node *n;
> + unsigned long flags;
> + unsigned long key;
> +
> + if (!ftrace_profile_hash)
> + return NULL;
> +
> + key = hash_long(ip, ftrace_profile_bits);
> + hhd = &ftrace_profile_hash[key];
> +
> + if (hlist_empty(hhd))
> + return NULL;
> +
> + local_irq_save(flags);
> + hlist_for_each_entry_rcu(rec, n, hhd, node) {
> + if (rec->ip == ip)
> + goto out;
> + }
> + rec = NULL;
> + out:
> + local_irq_restore(flags);
> +
> + return rec;
> +}
> +
> +static void
> +function_profile_call(unsigned long ip, unsigned long parent_ip)
> +{
> + struct dyn_ftrace *rec;
> + unsigned long flags;
> +
> + if (!ftrace_profile_enabled)
> + return;
> +
> + local_irq_save(flags);
> + rec = ftrace_find_profiled_func(ip);
> + if (!rec)
> + goto out;
> +
> + rec->counter++;
> + out:
> + local_irq_restore(flags);
> +}
> +
> +static struct ftrace_ops ftrace_profile_ops __read_mostly =
> +{
> + .func = function_profile_call,
> +};
> +
> +static ssize_t
> +ftrace_profile_write(struct file *filp, const char __user *ubuf,
> + size_t cnt, loff_t *ppos)
> +{
> + unsigned long val;
> + char buf[64];
> + int ret;
> +
> + if (!ftrace_profile_hash) {
> + pr_info("Can not enable hash due to earlier problems\n");
> + return -ENODEV;
> + }
> +
> + if (cnt >= sizeof(buf))
> + return -EINVAL;
> +
> + if (copy_from_user(&buf, ubuf, cnt))
> + return -EFAULT;
> +
> + buf[cnt] = 0;
> +
> + ret = strict_strtoul(buf, 10, &val);
> + if (ret < 0)
> + return ret;
> +
> + val = !!val;
> +
> + mutex_lock(&ftrace_profile_lock);
> + if (ftrace_profile_enabled ^ val) {
> + if (val) {
> + ftrace_profile_reset();
> + register_ftrace_function(&ftrace_profile_ops);
> + ftrace_profile_enabled = 1;
> + } else {
> + ftrace_profile_enabled = 0;
> + unregister_ftrace_function(&ftrace_profile_ops);
> + }
> + }
> + mutex_unlock(&ftrace_profile_lock);
> +
> + filp->f_pos += cnt;
> +
> + return cnt;
> +}
> +
> +static const struct file_operations ftrace_profile_fops = {
> + .open = tracing_open_generic,
> + .read = ftrace_profile_read,
> + .write = ftrace_profile_write,
> +};

I should really provide such helper per stat tracer.

Say, something like:

/debug/tracing/trace_stat/name/enable

Thanks,
Frederic.

> +
> +static void ftrace_profile_debugfs(struct dentry *d_tracer)
> +{
> + struct dentry *entry;
> + int ret;
> +
> + ret = register_stat_tracer(&function_stats);
> + if (ret) {
> + pr_warning("Warning: could not register "
> + "function stats\n");
> + return;
> + }
> +
> + entry = debugfs_create_file("function_profile_enabled", 0644,
> + d_tracer, NULL, &ftrace_profile_fops);
> + if (!entry)
> + pr_warning("Could not create debugfs "
> + "'function_profile_enabled' entry\n");
> +}
> +
> +static void ftrace_add_profile(struct dyn_ftrace *rec)
> +{
> + unsigned long key;
> +
> + if (!ftrace_profile_hash)
> + return;
> +
> + key = hash_long(rec->ip, ftrace_profile_bits);
> + hlist_add_head_rcu(&rec->node, &ftrace_profile_hash[key]);
> +}
> +
> +static void ftrace_profile_release(struct dyn_ftrace *rec)
> +{
> + mutex_lock(&ftrace_profile_lock);
> + hlist_del(&rec->node);
> + mutex_unlock(&ftrace_profile_lock);
> +}
> +
> +#else /* CONFIG_FUNCTION_PROFILER */
> +static void ftrace_profile_init(int nr_funcs)
> +{
> +}
> +static void ftrace_add_profile(struct dyn_ftrace *rec)
> +{
> +}
> +static void ftrace_profile_debugfs(struct dentry *d_tracer)
> +{
> +}
> +static void ftrace_profile_release(struct dyn_ftrace *rec)
> +{
> +}
> +#endif /* CONFIG_FUNCTION_PROFILER */
> +
> #ifdef CONFIG_KPROBES
>
> static int frozen_record_count;
> @@ -359,8 +660,10 @@ void ftrace_release(void *start, unsigned long size)
> mutex_lock(&ftrace_lock);
> do_for_each_ftrace_rec(pg, rec) {
> if ((rec->ip >= s) && (rec->ip < e) &&
> - !(rec->flags & FTRACE_FL_FREE))
> + !(rec->flags & FTRACE_FL_FREE)) {
> ftrace_free_rec(rec);
> + ftrace_profile_release(rec);
> + }
> } while_for_each_ftrace_rec();
> mutex_unlock(&ftrace_lock);
> }
> @@ -414,6 +717,8 @@ ftrace_record_ip(unsigned long ip)
> rec->newlist = ftrace_new_addrs;
> ftrace_new_addrs = rec;
>
> + ftrace_add_profile(rec);
> +
> return rec;
> }
>
> @@ -2157,6 +2462,8 @@ static __init int ftrace_init_dyn_debugfs(struct dentry *d_tracer)
> "'set_graph_function' entry\n");
> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>
> + ftrace_profile_debugfs(d_tracer);
> +
> return 0;
> }
>
> @@ -2225,6 +2532,8 @@ void __init ftrace_init(void)
> if (ret)
> goto failed;
>
> + ftrace_profile_init(count);
> +
> last_ftrace_enabled = ftrace_enabled = 1;
>
> ret = ftrace_convert_nops(NULL,
> --
> 1.6.2
>
> --