Re: [RFC rcu/next] torture: Stop onoff task if there is only one cpu

Josh Triplett
2016-05-02T17:19:04Z

On Mon, May 02, 2016 at 10:30:00AM +0800, Boqun Feng wrote:
> If the whole system has only one cpu, that cpu won't be able to be
> offlined, so there is no need onoff task is stil running.
>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
>
> I hit something like the following while I was running rcutorture
> in a guest with only one vCPU:
>
> [ 31.197457] rcu-torture:torture_onoff task: offlining 0
> [ 31.197508] rcu-torture:torture_onoff task: offline 0 failed: errno -16
>
> I know this is an expected behavior, but think we could just stop
> the onoff task if there is only one cpu.

I find it a little bit unfortunate that this kicks off a thread just to
immediately exit that thread, rather than never starting it in the first
place. However, it also seems like the most convenient solution here,
and I don't see much point in going out of the way to optimize this test
for uniprocessor systems.

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> kernel/torture.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/kernel/torture.c b/kernel/torture.c
> index fb39a06bbef5..a85b7d61d9dd 100644
> --- a/kernel/torture.c
> +++ b/kernel/torture.c
> @@ -194,6 +194,12 @@ torture_onoff(void *arg)
> for_each_online_cpu(cpu)
> maxcpu = cpu;
> WARN_ON(maxcpu < 0);
> +
> + if (maxcpu == 0) {
> + VERBOSE_TOROUT_STRING("only one cpu is found, onoff is impossible");
> + goto stop;
> + }
> +
> if (onoff_holdoff > 0) {
> VERBOSE_TOROUT_STRING("torture_onoff begin holdoff");
> schedule_timeout_interruptible(onoff_holdoff);
> @@ -209,6 +215,8 @@ torture_onoff(void *arg)
> &sum_online, &min_online, &max_online);
> schedule_timeout_interruptible(onoff_interval);
> }
> +
> +stop:
> torture_kthread_stopping("torture_onoff");
> return 0;
> }
> --
> 2.8.0
>