We setting clock_skip_update = 1 based on the assumption that the
next call to update_rq_clock() will come nearly immediately
after being set. However, it is not always true especially on
non-preempt mode. In this case we may miss some clock update, which
would cause an error curr->sum_exec_runtime account.
The test result show that test_kthread's exec_runtime has been
added to watchdog.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ P COMMAND
28 root RT 0 0 0 0 S 100 0.0 0:05.39 5 watchdog/5
7 root RT 0 0 0 0 S 95 0.0 0:05.83 0 watchdog/0
12 root RT 0 0 0 0 S 94 0.0 0:05.79 1 watchdog/1
16 root RT 0 0 0 0 S 92 0.0 0:05.74 2 watchdog/2
20 root RT 0 0 0 0 S 91 0.0 0:05.71 3 watchdog/3
24 root RT 0 0 0 0 S 82 0.0 0:05.42 4 watchdog/4
32 root RT 0 0 0 0 S 79 0.0 0:05.35 6 watchdog/6
5200 root 20 0 0 0 0 R 21 0.0 0:08.88 6 test_kthread/6
5194 root 20 0 0 0 0 R 20 0.0 0:08.41 0 test_kthread/0
5195 root 20 0 0 0 0 R 20 0.0 0:08.44 1 test_kthread/1
5196 root 20 0 0 0 0 R 20 0.0 0:08.49 2 test_kthread/2
5197 root 20 0 0 0 0 R 20 0.0 0:08.53 3 test_kthread/3
5198 root 20 0 0 0 0 R 19 0.0 0:08.81 4 test_kthread/4
5199 root 20 0 0 0 0 R 2 0.0 0:08.66 5 test_kthread/5
"test_kthread/i" is a kernel thread which has a infinity loop and it calls
schedule() every 1s. It's main process as below:
static int main_loop (void *unused)
{
unsigned long flags;
unsigned long last = jiffies;
int i;
while (!kthread_should_stop()) {
/* call schedule every 1 sec */
if (HZ <= jiffies - last) {
last = jiffies;
schedule();
}
/* do some thing */
for (i = 0; i < 1000; i++)
;
if (kthread_should_stop())
break;
}
}
In this patch, we do not skip clock update when current task is kernel
thread in non-preempt mode.
Reported-by: Zhang Hang <bob.zhanghang@xxxxxxxxxx>
Signed-off-by: Xie XiuQi <xiexiuqi@xxxxxxxxxx>
---
kernel/sched/core.c | 11 +++++++++++
1 files changed, 11 insertions(+), 0 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e8b3350..018dc43 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -970,8 +970,19 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
* A queue event has occurred, and we're going to schedule. In
* this case, we can save a useless back to back clock update.
*/
+#ifdef CONFIG_PREEMPT
if (rq->curr->on_rq && test_tsk_need_resched(rq->curr))
rq->skip_clock_update = 1;
+#else
+ /*
+ * In non-preempt mode, a kernel thread may run for a long time
+ * until been scheduled out by itself. In this cace, we need update
+ * rq clock when calling schedule function, otherwise, we might
+ * miss rq clock update for a long time.
+ */
+ if (rq->curr->on_rq && test_tsk_need_resched(rq->curr) && rq->curr->mm)
+ rq->skip_clock_update = 1;
+#endif
}
static ATOMIC_NOTIFIER_HEAD(task_migration_notifier);
--
1.7.6.1
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