On Mon, Jul 01, 2013 at 02:45:04PM +0800, Xie XiuQi wrote:
> 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(-)
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read Documentation/stable_kernel_rules.txt
for how to do this properly.
</formletter>
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