[PATCH] sleep profiling

Implement prof=sleep profiling.  TASK_UNINTERRUPTIBLE sleeps will be taken
as a profile hit, and every millisecond spent sleeping causes a profile-hit
for the call site that initiated the sleep.

Sample readprofile output on i386:

   306 ps2_sendbyte                               1.3973
   432 call_usermodehelper_keys                   1.9548
   484 ps2_command                                0.6453
   790 __driver_attach                            4.7879
  1593 msleep                                    44.2500
  3976 sync_buffer                               64.1290
  4076 do_lookup                                 12.4648
  8587 sync_page                                122.6714
 20820 total                                      0.0067

(NOTE: architectures need to check whether get_wchan() can be called from
deep within the wakeup path.)

akpm: we need to mark more functions __sched.  lock_sock(), msleep(), others..

akpm: the contention in do_lookup() is a surprise.  Presumably doing disk
reads for directory contents while holding i_mutex.

[akpm@osdl.org: various fixes]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 41 insertions, 9 deletions

diff --git a/kernel/profile.c b/kernel/profile.c
index 15b012df4ff1..04fd84e8cdbe 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -40,7 +40,7 @@ int (*timer_hook)(struct pt_regs *) __read_mostly;
 
 static atomic_t *prof_buffer;
 static unsigned long prof_len, prof_shift;
-static int prof_on __read_mostly;
+int prof_on __read_mostly;
 static cpumask_t prof_cpu_mask = CPU_MASK_ALL;
 #ifdef CONFIG_SMP
 static DEFINE_PER_CPU(struct profile_hit *[2], cpu_profile_hits);
@@ -51,9 +51,19 @@ static DEFINE_MUTEX(profile_flip_mutex);
 static int __init profile_setup(char * str)
 {
         static char __initdata schedstr[] = "schedule";
+        static char __initdata sleepstr[] = "sleep";
         int par;
 
-        if (!strncmp(str, schedstr, strlen(schedstr))) {
+        if (!strncmp(str, sleepstr, strlen(sleepstr))) {
+                prof_on = SLEEP_PROFILING;
+                if (str[strlen(sleepstr)] == ',')
+                        str += strlen(sleepstr) + 1;
+                if (get_option(&str, &par))
+                        prof_shift = par;
+                printk(KERN_INFO
+                        "kernel sleep profiling enabled (shift: %ld)\n",
+                        prof_shift);
+        } else if (!strncmp(str, sleepstr, strlen(sleepstr))) {
                 prof_on = SCHED_PROFILING;
                 if (str[strlen(schedstr)] == ',')
                         str += strlen(schedstr) + 1;
@@ -204,7 +214,8 @@ EXPORT_SYMBOL_GPL(profile_event_unregister);
  * positions to which hits are accounted during short intervals (e.g.
  * several seconds) is usually very small. Exclusion from buffer
  * flipping is provided by interrupt disablement (note that for
- * SCHED_PROFILING profile_hit() may be called from process context).
+ * SCHED_PROFILING or SLEEP_PROFILING profile_hit() may be called from
+ * process context).
  * The hash function is meant to be lightweight as opposed to strong,
  * and was vaguely inspired by ppc64 firmware-supported inverted
  * pagetable hash functions, but uses a full hashtable full of finite
@@ -257,7 +268,7 @@ static void profile_discard_flip_buffers(void)
         mutex_unlock(&profile_flip_mutex);
 }
 
-void profile_hit(int type, void *__pc)
+void profile_hits(int type, void *__pc, unsigned int nr_hits)
 {
         unsigned long primary, secondary, flags, pc = (unsigned long)__pc;
         int i, j, cpu;
@@ -274,21 +285,31 @@ void profile_hit(int type, void *__pc)
                 put_cpu();
                 return;
         }
+        /*
+         * We buffer the global profiler buffer into a per-CPU
+         * queue and thus reduce the number of global (and possibly
+         * NUMA-alien) accesses. The write-queue is self-coalescing:
+         */
         local_irq_save(flags);
         do {
                 for (j = 0; j < PROFILE_GRPSZ; ++j) {
                         if (hits[i + j].pc == pc) {
-                                hits[i + j].hits++;
+                                hits[i + j].hits += nr_hits;
                                 goto out;
                         } else if (!hits[i + j].hits) {
                                 hits[i + j].pc = pc;
-                                hits[i + j].hits = 1;
+                                hits[i + j].hits = nr_hits;
                                 goto out;
                         }
                 }
                 i = (i + secondary) & (NR_PROFILE_HIT - 1);
         } while (i != primary);
-        atomic_inc(&prof_buffer[pc]);
+
+        /*
+         * Add the current hit(s) and flush the write-queue out
+         * to the global buffer:
+         */
+        atomic_add(nr_hits, &prof_buffer[pc]);
         for (i = 0; i < NR_PROFILE_HIT; ++i) {
                 atomic_add(hits[i].hits, &prof_buffer[hits[i].pc]);
                 hits[i].pc = hits[i].hits = 0;
@@ -356,14 +377,14 @@ static int __devinit profile_cpu_callback(struct notifier_block *info,
 #define profile_flip_buffers()          do { } while (0)
 #define profile_discard_flip_buffers()  do { } while (0)
 
-void profile_hit(int type, void *__pc)
+void profile_hits(int type, void *__pc, unsigned int nr_hits)
 {
         unsigned long pc;
 
         if (prof_on != type || !prof_buffer)
                 return;
         pc = ((unsigned long)__pc - (unsigned long)_stext) >> prof_shift;
-        atomic_inc(&prof_buffer[min(pc, prof_len - 1)]);
+        atomic_add(nr_hits, &prof_buffer[min(pc, prof_len - 1)]);
 }
 #endif /* !CONFIG_SMP */
 
diff --git a/kernel/sched.c b/kernel/sched.c
index 343e1794233e..75a005ed4eda 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -948,6 +948,17 @@ static void activate_task(struct task_struct *p, struct rq *rq, int local)
         }
 #endif
 
+        /*
+         * Sleep time is in units of nanosecs, so shift by 20 to get a
+         * milliseconds-range estimation of the amount of time that the task
+         * spent sleeping:
+         */
+        if (unlikely(prof_on == SLEEP_PROFILING)) {
+                if (p->state == TASK_UNINTERRUPTIBLE)
+                        profile_hits(SLEEP_PROFILING, (void *)get_wchan(p),
+                                     (now - p->timestamp) >> 20);
+        }
+
         if (!rt_task(p))
                 p->prio = recalc_task_prio(p, now);