Re: [PATCH 3/5] rcu,nohz: run vtime_user_enter/exit only when state == IN_USER

Paul E. McKenney
2015-02-10T21:36:06Z

On Tue, Feb 10, 2015 at 03:27:52PM -0500, riel@redhat.com wrote:
> From: Rik van Riel <riel@redhat.com>
>
> Only run vtime_user_enter, vtime_user_exit, and the user enter & exit
> trace points when we are entering or exiting user state, respectively.
>
> The KVM code in guest_enter and guest_exit already take care of calling
> vtime_guest_enter and vtime_guest_exit, respectively.
>
> The RCU code only distinguishes between "idle" and "not idle or kernel".
> There should be no need to add an additional (unused) state there.
>
> Signed-off-by: Rik van Riel <riel@redhat.com>

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
> kernel/context_tracking.c | 12 ++++++++----
> 1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 38e38aeac8b9..0e4e318d5ea4 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -77,7 +77,6 @@ void context_tracking_enter(enum ctx_state state)
> local_irq_save(flags);
> if ( __this_cpu_read(context_tracking.state) != state) {
> if (__this_cpu_read(context_tracking.active)) {
> - trace_user_enter(0);
> /*
> * At this stage, only low level arch entry code remains and
> * then we'll run in userspace. We can assume there won't be
> @@ -85,7 +84,10 @@ void context_tracking_enter(enum ctx_state state)
> * user_exit() or rcu_irq_enter(). Let's remove RCU's dependency
> * on the tick.
> */
> - vtime_user_enter(current);
> + if (state == IN_USER) {
> + trace_user_enter(0);
> + vtime_user_enter(current);
> + }
> rcu_user_enter();
> }
> /*
> @@ -143,8 +145,10 @@ void context_tracking_exit(enum ctx_state state)
> * RCU core about that (ie: we may need the tick again).
> */
> rcu_user_exit();
> - vtime_user_exit(current);
> - trace_user_exit(0);
> + if (state == IN_USER) {
> + vtime_user_exit(current);
> + trace_user_exit(0);
> + }
> }
> __this_cpu_write(context_tracking.state, IN_KERNEL);
> }
> --
> 1.9.3
>