tracing: profile likely and unlikely annotations

Impact: new unlikely/likely profiler

Andrew Morton recently suggested having an in-kernel way to profile
likely and unlikely macros. This patch achieves that goal.

When configured, every(*) likely and unlikely macro gets a counter attached
to it. When the condition is hit, the hit and misses of that condition
are recorded. These numbers can later be retrieved by:

  /debugfs/tracing/profile_likely    - All likely markers
  /debugfs/tracing/profile_unlikely  - All unlikely markers.

# cat /debug/tracing/profile_unlikely | head
 correct incorrect  %        Function                  File              Line
 ------- ---------  -        --------                  ----              ----
    2167        0   0 do_arch_prctl                  process_64.c         832
       0        0   0 do_arch_prctl                  process_64.c         804
    2670        0   0 IS_ERR                         err.h                34
   71230     5693   7 __switch_to                    process_64.c         673
   76919        0   0 __switch_to                    process_64.c         639
   43184    33743  43 __switch_to                    process_64.c         624
   12740    64181  83 __switch_to                    process_64.c         594
   12740    64174  83 __switch_to                    process_64.c         590

# cat /debug/tracing/profile_unlikely | \
  awk '{ if ($3 > 25) print $0; }' |head -20
   44963    35259  43 __switch_to                    process_64.c         624
   12762    67454  84 __switch_to                    process_64.c         594
   12762    67447  84 __switch_to                    process_64.c         590
    1478      595  28 syscall_get_error              syscall.h            51
       0     2821 100 syscall_trace_leave            ptrace.c             1567
       0        1 100 native_smp_prepare_cpus        smpboot.c            1237
   86338   265881  75 calc_delta_fair                sched_fair.c         408
  210410   108540  34 calc_delta_mine                sched.c              1267
       0    54550 100 sched_info_queued              sched_stats.h        222
   51899    66435  56 pick_next_task_fair            sched_fair.c         1422
       6       10  62 yield_task_fair                sched_fair.c         982
    7325     2692  26 rt_policy                      sched.c              144
       0     1270 100 pre_schedule_rt                sched_rt.c           1261
    1268    48073  97 pick_next_task_rt              sched_rt.c           884
       0    45181 100 sched_info_dequeued            sched_stats.h        177
       0       15 100 sched_move_task                sched.c              8700
       0       15 100 sched_move_task                sched.c              8690
   53167    33217  38 schedule                       sched.c              4457
       0    80208 100 sched_info_switch              sched_stats.h        270
   30585    49631  61 context_switch                 sched.c              2619

# cat /debug/tracing/profile_likely | awk '{ if ($3 > 25) print $0; }'
   39900    36577  47 pick_next_task                 sched.c              4397
   20824    15233  42 switch_mm                      mmu_context_64.h     18
       0        7 100 __cancel_work_timer            workqueue.c          560
     617    66484  99 clocksource_adjust             timekeeping.c        456
       0   346340 100 audit_syscall_exit             auditsc.c            1570
      38   347350  99 audit_get_context              auditsc.c            732
       0   345244 100 audit_syscall_entry            auditsc.c            1541
      38     1017  96 audit_free                     auditsc.c            1446
       0     1090 100 audit_alloc                    auditsc.c            862
    2618     1090  29 audit_alloc                    auditsc.c            858
       0        6 100 move_masked_irq                migration.c          9
       1      198  99 probe_sched_wakeup             trace_sched_switch.c 58
       2        2  50 probe_wakeup                   trace_sched_wakeup.c 227
       0        2 100 probe_wakeup_sched_switch      trace_sched_wakeup.c 144
    4514     2090  31 __grab_cache_page              filemap.c            2149
   12882   228786  94 mapping_unevictable            pagemap.h            50
       4       11  73 __flush_cpu_slab               slub.c               1466
  627757   330451  34 slab_free                      slub.c               1731
    2959    61245  95 dentry_lru_del_init            dcache.c             153
     946     1217  56 load_elf_binary                binfmt_elf.c         904
     102       82  44 disk_put_part                  genhd.h              206
       1        1  50 dst_gc_task                    dst.c                82
       0       19 100 tcp_mss_split_point            tcp_output.c         1126

As you can see by the above, there's a bit of work to do in rethinking
the use of some unlikelys and likelys. Note: the unlikely case had 71 hits
that were more than 25%.

Note:  After submitting my first version of this patch, Andrew Morton
  showed me a version written by Daniel Walker, where I picked up
  the following ideas from:

  1)  Using __builtin_constant_p to avoid profiling fixed values.
  2)  Using __FILE__ instead of instruction pointers.
  3)  Using the preprocessor to stop all profiling of likely
       annotations from vsyscall_64.c.

Thanks to Andrew Morton, Arjan van de Ven, Theodore Tso and Ingo Molnar
for their feed back on this patch.

(*) Not ever unlikely is recorded, those that are used by vsyscalls
 (a few of them) had to have profiling disabled.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Theodore Tso <tytso@mit.edu>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Rostedt 2008-11-12 00:14:39 -05:00 committed by Ingo Molnar
parent cb9382e5a9
commit 1f0d69a9fc
6 changed files with 261 additions and 3 deletions

View file

@ -17,6 +17,14 @@
* want per guest time just set the kernel.vsyscall64 sysctl to 0.
*/
/* Protect userspace from profiling */
#ifdef CONFIG_TRACE_UNLIKELY_PROFILE
# undef likely
# undef unlikely
# define likely(x) likely_notrace(x)
# define unlikely(x) unlikely_notrace(x)
#endif
#include <linux/time.h>
#include <linux/init.h>
#include <linux/kernel.h>

View file

@ -45,6 +45,17 @@
#define MCOUNT_REC()
#endif
#ifdef CONFIG_TRACE_UNLIKELY_PROFILE
#define LIKELY_PROFILE() VMLINUX_SYMBOL(__start_likely_profile) = .; \
*(_ftrace_likely) \
VMLINUX_SYMBOL(__stop_likely_profile) = .; \
VMLINUX_SYMBOL(__start_unlikely_profile) = .; \
*(_ftrace_unlikely) \
VMLINUX_SYMBOL(__stop_unlikely_profile) = .;
#else
#define LIKELY_PROFILE()
#endif
/* .data section */
#define DATA_DATA \
*(.data) \
@ -62,7 +73,8 @@
VMLINUX_SYMBOL(__stop___markers) = .; \
VMLINUX_SYMBOL(__start___tracepoints) = .; \
*(__tracepoints) \
VMLINUX_SYMBOL(__stop___tracepoints) = .;
VMLINUX_SYMBOL(__stop___tracepoints) = .; \
LIKELY_PROFILE()
#define RO_DATA(align) \
. = ALIGN((align)); \

View file

@ -59,8 +59,65 @@ extern void __chk_io_ptr(const volatile void __iomem *);
* specific implementations come from the above header files
*/
#define likely(x) __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#ifdef CONFIG_TRACE_UNLIKELY_PROFILE
struct ftrace_likely_data {
const char *func;
const char *file;
unsigned line;
unsigned long correct;
unsigned long incorrect;
};
void ftrace_likely_update(struct ftrace_likely_data *f, int val, int expect);
#define likely_notrace(x) __builtin_expect(!!(x), 1)
#define unlikely_notrace(x) __builtin_expect(!!(x), 0)
#define likely_check(x) ({ \
int ______r; \
static struct ftrace_likely_data \
__attribute__((__aligned__(4))) \
__attribute__((section("_ftrace_likely"))) \
______f = { \
.func = __func__, \
.file = __FILE__, \
.line = __LINE__, \
}; \
______f.line = __LINE__; \
______r = likely_notrace(x); \
ftrace_likely_update(&______f, ______r, 1); \
______r; \
})
#define unlikely_check(x) ({ \
int ______r; \
static struct ftrace_likely_data \
__attribute__((__aligned__(4))) \
__attribute__((section("_ftrace_unlikely"))) \
______f = { \
.func = __func__, \
.file = __FILE__, \
.line = __LINE__, \
}; \
______f.line = __LINE__; \
______r = unlikely_notrace(x); \
ftrace_likely_update(&______f, ______r, 0); \
______r; \
})
/*
* Using __builtin_constant_p(x) to ignore cases where the return
* value is always the same. This idea is taken from a similar patch
* written by Daniel Walker.
*/
# ifndef likely
# define likely(x) (__builtin_constant_p(x) ? !!(x) : likely_check(x))
# endif
# ifndef unlikely
# define unlikely(x) (__builtin_constant_p(x) ? !!(x) : unlikely_check(x))
# endif
#else
# define likely(x) __builtin_expect(!!(x), 1)
# define unlikely(x) __builtin_expect(!!(x), 0)
#endif
/* Optimization barrier */
#ifndef barrier

View file

@ -159,6 +159,22 @@ config BOOT_TRACER
selected, because the self-tests are an initcall as well and that
would invalidate the boot trace. )
config TRACE_UNLIKELY_PROFILE
bool "Trace likely/unlikely profiler"
depends on DEBUG_KERNEL
select TRACING
help
This tracer profiles all the the likely and unlikely macros
in the kernel. It will display the results in:
/debugfs/tracing/profile_likely
/debugfs/tracing/profile_unlikely
Note: this will add a significant overhead, only turn this
on if you need to profile the system's use of these macros.
Say N if unsure.
config STACK_TRACER
bool "Trace max stack"
depends on HAVE_FUNCTION_TRACER

View file

@ -25,5 +25,6 @@ obj-$(CONFIG_STACK_TRACER) += trace_stack.o
obj-$(CONFIG_MMIOTRACE) += trace_mmiotrace.o
obj-$(CONFIG_BOOT_TRACER) += trace_boot.o
obj-$(CONFIG_FUNCTION_RET_TRACER) += trace_functions_return.o
obj-$(CONFIG_TRACE_UNLIKELY_PROFILE) += trace_unlikely.o
libftrace-y := ftrace.o

View file

@ -0,0 +1,164 @@
/*
* unlikely profiler
*
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/kallsyms.h>
#include <linux/seq_file.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/ftrace.h>
#include <linux/hash.h>
#include <linux/fs.h>
#include <asm/local.h>
#include "trace.h"
void ftrace_likely_update(struct ftrace_likely_data *f, int val, int expect)
{
/* FIXME: Make this atomic! */
if (val == expect)
f->correct++;
else
f->incorrect++;
}
EXPORT_SYMBOL(ftrace_likely_update);
struct ftrace_pointer {
void *start;
void *stop;
};
static void *
t_next(struct seq_file *m, void *v, loff_t *pos)
{
struct ftrace_pointer *f = m->private;
struct ftrace_likely_data *p = v;
(*pos)++;
if (v == (void *)1)
return f->start;
++p;
if ((void *)p >= (void *)f->stop)
return NULL;
return p;
}
static void *t_start(struct seq_file *m, loff_t *pos)
{
void *t = (void *)1;
loff_t l = 0;
for (; t && l < *pos; t = t_next(m, t, &l))
;
return t;
}
static void t_stop(struct seq_file *m, void *p)
{
}
static int t_show(struct seq_file *m, void *v)
{
struct ftrace_likely_data *p = v;
const char *f;
unsigned long percent;
if (v == (void *)1) {
seq_printf(m, " correct incorrect %% "
" Function "
" File Line\n"
" ------- --------- - "
" -------- "
" ---- ----\n");
return 0;
}
/* Only print the file, not the path */
f = p->file + strlen(p->file);
while (f >= p->file && *f != '/')
f--;
f++;
if (p->correct) {
percent = p->incorrect * 100;
percent /= p->correct + p->incorrect;
} else
percent = p->incorrect ? 100 : 0;
seq_printf(m, "%8lu %8lu %3lu ", p->correct, p->incorrect, percent);
seq_printf(m, "%-30.30s %-20.20s %d\n", p->func, f, p->line);
return 0;
}
static struct seq_operations tracing_likely_seq_ops = {
.start = t_start,
.next = t_next,
.stop = t_stop,
.show = t_show,
};
static int tracing_likely_open(struct inode *inode, struct file *file)
{
int ret;
ret = seq_open(file, &tracing_likely_seq_ops);
if (!ret) {
struct seq_file *m = file->private_data;
m->private = (void *)inode->i_private;
}
return ret;
}
static struct file_operations tracing_likely_fops = {
.open = tracing_likely_open,
.read = seq_read,
.llseek = seq_lseek,
};
extern unsigned long __start_likely_profile[];
extern unsigned long __stop_likely_profile[];
extern unsigned long __start_unlikely_profile[];
extern unsigned long __stop_unlikely_profile[];
static struct ftrace_pointer ftrace_likely_pos = {
.start = __start_likely_profile,
.stop = __stop_likely_profile,
};
static struct ftrace_pointer ftrace_unlikely_pos = {
.start = __start_unlikely_profile,
.stop = __stop_unlikely_profile,
};
static __init int ftrace_unlikely_init(void)
{
struct dentry *d_tracer;
struct dentry *entry;
d_tracer = tracing_init_dentry();
entry = debugfs_create_file("profile_likely", 0444, d_tracer,
&ftrace_likely_pos,
&tracing_likely_fops);
if (!entry)
pr_warning("Could not create debugfs 'profile_likely' entry\n");
entry = debugfs_create_file("profile_unlikely", 0444, d_tracer,
&ftrace_unlikely_pos,
&tracing_likely_fops);
if (!entry)
pr_warning("Could not create debugfs"
" 'profile_unlikely' entry\n");
return 0;
}
device_initcall(ftrace_unlikely_init);