sched: Provide iowait counters

For counting how long an application has been waiting for
(disk) IO, there currently is only the HZ sample driven
information available, while for all other counters in this
class, a high resolution version is available via
CONFIG_SCHEDSTATS.

In order to make an improved bootchart tool possible, we also
need a higher resolution version of the iowait time.

This patch below adds this scheduler statistic to the kernel.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4A64B813.1080506@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e209ae0e7a8a..9c96ef2f7e68 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1111,6 +1111,8 @@ struct sched_entity {
         u64                     wait_max;
         u64                     wait_count;
         u64                     wait_sum;
+        u64                     iowait_count;
+        u64                     iowait_sum;
 
         u64                     sleep_start;
         u64                     sleep_max;
@@ -1231,6 +1233,8 @@ struct task_struct {
         unsigned did_exec:1;
         unsigned in_execve:1;   /* Tell the LSMs that the process is doing an
                                  * execve */
+        unsigned in_iowait:1;
+
 
         /* Revert to default priority/policy when forking */
         unsigned sched_reset_on_fork:1;
diff --git a/kernel/sched.c b/kernel/sched.c
index 6244d24cafc1..38d05a89e0f2 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6754,7 +6754,9 @@ void __sched io_schedule(void)
 
         delayacct_blkio_start();
         atomic_inc(&rq->nr_iowait);
+        current->in_iowait = 1;
         schedule();
+        current->in_iowait = 0;
         atomic_dec(&rq->nr_iowait);
         delayacct_blkio_end();
 }
@@ -6767,7 +6769,9 @@ long __sched io_schedule_timeout(long timeout)
 
         delayacct_blkio_start();
         atomic_inc(&rq->nr_iowait);
+        current->in_iowait = 1;
         ret = schedule_timeout(timeout);
+        current->in_iowait = 0;
         atomic_dec(&rq->nr_iowait);
         delayacct_blkio_end();
         return ret;
diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c
index 70c7e0b79946..5ddbd0891267 100644
--- a/kernel/sched_debug.c
+++ b/kernel/sched_debug.c
@@ -409,6 +409,8 @@ void proc_sched_show_task(struct task_struct *p, struct seq_file *m)
         PN(se.wait_max);
         PN(se.wait_sum);
         P(se.wait_count);
+        PN(se.iowait_sum);
+        P(se.iowait_count);
         P(sched_info.bkl_count);
         P(se.nr_migrations);
         P(se.nr_migrations_cold);
@@ -479,6 +481,8 @@ void proc_sched_set_task(struct task_struct *p)
         p->se.wait_max                          = 0;
         p->se.wait_sum                          = 0;
         p->se.wait_count                        = 0;
+        p->se.iowait_sum                        = 0;
+        p->se.iowait_count                      = 0;
         p->se.sleep_max                         = 0;
         p->se.sum_sleep_runtime                 = 0;
         p->se.block_max                         = 0;
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 342000b31ad6..471fa281f5e0 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -652,6 +652,11 @@ static void enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
                 se->sum_sleep_runtime += delta;
 
                 if (tsk) {
+                        if (tsk->in_iowait) {
+                                se->iowait_sum += delta;
+                                se->iowait_count++;
+                        }
+
                         /*
                          * Blocking time is in units of nanosecs, so shift by
                          * 20 to get a milliseconds-range estimation of the