linux-kernel - Re: [PATCH 3/5] rcu,nohz: run vtime_user_enter/exit only when state == IN

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Date:	Tue, 10 Feb 2015 13:35:59 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	riel@...hat.com
Cc:	fweisbec@...il.com, luto@...capital.net, will.deacon@....com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	mtosatti@...hat.com, borntraeger@...ibm.com,
	lcapitulino@...hat.com, pbonzini@...hat.com
Subject: Re: [PATCH 3/5] rcu,nohz: run vtime_user_enter/exit only when state
 == IN_USER

On Tue, Feb 10, 2015 at 03:27:52PM -0500, riel@...hat.com wrote:
> From: Rik van Riel <riel@...hat.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@...hat.com>

Reviewed-by: Paul E. McKenney <paulmck@...ux.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
> 

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