Re: [PATCH] rcu-tasks: Avoid rtp_irq_work triggering when the rcu-tasks GP is ongoing

[Z qiang]

>
> This commit generate rcu_task_gp_in_progress() to check whether
> the rcu-tasks GP is ongoing, if is ongoing, avoid trigger
> rtp_irq_work to wakeup rcu tasks kthreads in call_rcu_tasks_generic().
>
> The test results are as follows:
>
> echo call_rcu_tasks_iw_wakeup > /sys/kernel/debug/tracing/set_ftrace_filter
> echo 1 > /sys/kernel/debug/tracing/function_profile_enabled
> insmod rcutorture.ko torture_type=tasks-tracing fwd_progress=4
> sleep 600
> rmmod rcutorture.ko
> echo 0 > /sys/kernel/debug/tracing/function_profile_enabled
> echo > /sys/kernel/debug/tracing/set_ftrace_filter
>
> head /sys/kernel/debug/tracing/trace_stat/function*
>
> original: 56376  apply patch: 33521
>
> Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
> ---
>

This test is based on the following environment:
runqemu nographic kvm slirp qemuparams="-smp 4 -m 2048M -drive
file=$PWD/share.img,if=virtio"  -d

Thanks
Zqiang

> original:
> ==> /sys/kernel/debug/tracing/trace_stat/function0 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup             13217    19292.52 us     1.459 us        8.834 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function1 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup             15146    22377.01 us     1.477 us        22.873 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function2 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup             12561    18125.76 us     1.443 us        6.372 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function3 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup             15452    21770.57 us     1.408 us        6.710 us
>
> apply patch:
> ==> /sys/kernel/debug/tracing/trace_stat/function0 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup              8334    15121.13 us     1.814 us        4.457 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function1 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup              8355    15760.51 us     1.886 us        14.775 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function2 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup              7219    14194.27 us     1.966 us        42.440 us
>
> ==> /sys/kernel/debug/tracing/trace_stat/function3 <==
>   Function                               Hit    Time            Avg             s^2
>   --------                               ---    ----            ---             ---
>   call_rcu_tasks_iw_wakeup              9613    19850.04 us     2.064 us        91.023 us
>
>  kernel/rcu/tasks.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 147b5945d67a..36c7e1d441d0 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -317,6 +317,11 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
>         rcuwait_wake_up(&rtp->cbs_wait);
>  }
>
> +static int rcu_task_gp_in_progress(struct rcu_tasks *rtp)
> +{
> +       return rcu_seq_state(rcu_seq_current(&rtp->tasks_gp_seq));
> +}
> +
>  // Enqueue a callback for the specified flavor of Tasks RCU.
>  static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>                                    struct rcu_tasks *rtp)
> @@ -375,7 +380,8 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>         }
>         rcu_read_unlock();
>         /* We can't create the thread unless interrupts are enabled. */
> -       if (needwake && READ_ONCE(rtp->kthread_ptr))
> +       if (needwake && READ_ONCE(rtp->kthread_ptr) &&
> +                       !rcu_task_gp_in_progress(rtp))
>                 irq_work_queue(&rtpcp->rtp_irq_work);
>  }
>
> --
> 2.17.1
>