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From: Frederic Weisbecker <fweisbec@gmail.com>
To: riel@redhat.com
Cc: kvm@vger.kernel.org, borntraeger@de.ibm.com,
	linux-kernel@vger.kernel.org, mtosatti@redhat.com,
	mingo@kernel.orgm, ak@linux.intel.com, oleg@redhat.com,
	masami.hiramatsu.pt@hitachi.com, paulmck@linux.vnet.ibm.com,
	lcapitulino@redhat.com, pbonzini@redhat.com
Subject: Re: [PATCH 4/5] kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest
Date: Fri, 6 Feb 2015 19:01:03 +0100	[thread overview]
Message-ID: <20150206180056.GD21905@lerouge> (raw)
In-Reply-To: <1423167832-17609-5-git-send-email-riel@redhat.com>

On Thu, Feb 05, 2015 at 03:23:51PM -0500, riel@redhat.com wrote:
> From: Rik van Riel <riel@redhat.com>
> 
> The host kernel is not doing anything while the CPU is executing
> a KVM guest VCPU, so it can be marked as being in an extended
> quiescent state, identical to that used when running user space
> code.
> 
> The only exception to that rule is when the host handles an
> interrupt, which is already handled by the irq code, which
> calls rcu_irq_enter and rcu_irq_exit.
> 
> The guest_enter and guest_exit functions already switch vtime
> accounting independent of context tracking, so leave those calls
> where they are, instead of moving them into the context tracking
> code.
> 
> Signed-off-by: Rik van Riel <riel@redhat.com>
> ---
>  include/linux/context_tracking.h       | 8 +++++++-
>  include/linux/context_tracking_state.h | 1 +
>  include/linux/kvm_host.h               | 3 ++-
>  3 files changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index bd9f000fc98d..a5d3bb44b897 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -43,7 +43,7 @@ static inline enum ctx_state exception_enter(void)
>  static inline void exception_exit(enum ctx_state prev_ctx)
>  {
>  	if (context_tracking_is_enabled()) {
> -		if (prev_ctx == IN_USER)
> +		if (prev_ctx == IN_USER || prev_ctx == IN_GUEST)
>  			context_tracking_user_enter(prev_ctx);
>  	}
>  }
> @@ -78,6 +78,9 @@ static inline void guest_enter(void)
>  		vtime_guest_enter(current);
>  	else
>  		current->flags |= PF_VCPU;
> +
> +	if (context_tracking_is_enabled())
> +		context_tracking_user_enter(IN_GUEST);

So you should probably just call rcu_user_enter() directly from
there. context_tracking_user_enter() is really about userspace
boundaries.

>  }
>  
>  static inline void guest_exit(void)
> @@ -86,6 +89,9 @@ static inline void guest_exit(void)
>  		vtime_guest_exit(current);
>  	else
>  		current->flags &= ~PF_VCPU;
> +
> +	if (context_tracking_is_enabled())
> +		context_tracking_user_exit(IN_GUEST);
>  }
>  
>  #else
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index 97a81225d037..f3ef027af749 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -15,6 +15,7 @@ struct context_tracking {
>  	enum ctx_state {
>  		IN_KERNEL = 0,
>  		IN_USER,
> +		IN_GUEST,
>  	} state;
>  };
>  
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 26f106022c88..c7828a6a9614 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -772,7 +772,8 @@ static inline void kvm_guest_enter(void)
>  	 * one time slice). Lets treat guest mode as quiescent state, just like
>  	 * we do with user-mode execution.
>  	 */
> -	rcu_virt_note_context_switch(smp_processor_id());
> +	if (!context_tracking_cpu_is_enabled())
> +		rcu_virt_note_context_switch(smp_processor_id());

Should we have a specific CONFIG for this feature? Or relying on full dynticks
to be enabled (and thus context tracking enabled) is enough?

Thanks.

>  }
>  
>  static inline void kvm_guest_exit(void)
> -- 
> 1.9.3
> 

  parent reply	other threads:[~2015-02-06 18:01 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-02-05 20:23 [PATCH v2 0/5] rcu,nohz,kvm: " riel
2015-02-05 20:23 ` [PATCH 1/5] rcu,nohz: add state parameter to context_tracking_user_enter/exit riel
2015-02-05 23:55   ` Paul E. McKenney
2015-02-06 10:15     ` Paolo Bonzini
2015-02-06 13:41       ` Paul E. McKenney
2015-02-06 17:22   ` Frederic Weisbecker
2015-02-06 18:20     ` Rik van Riel
2015-02-06 18:23       ` Frederic Weisbecker
2015-02-06 18:51         ` Rik van Riel
2015-02-06 23:15           ` Frederic Weisbecker
2015-02-07  3:53             ` Rik van Riel
2015-02-07  6:34               ` Paul E. McKenney
2015-02-07  7:14                 ` Paul E. McKenney
2015-02-07  8:30                   ` Frederic Weisbecker
2015-02-07 11:29                     ` Rik van Riel
2015-02-07 20:06                     ` Paul E. McKenney
2015-02-09 15:42                       ` Rik van Riel
2015-02-05 20:23 ` [PATCH 2/5] rcu,nohz: run vtime_user_enter/exit only when state == IN_USER riel
2015-02-05 20:23 ` [PATCH 3/5] nohz,kvm: export context_tracking_user_enter/exit riel
2015-02-05 23:55   ` Paul E. McKenney
2015-02-05 20:23 ` [PATCH 4/5] kvm,rcu,nohz: use RCU extended quiescent state when running KVM guest riel
2015-02-05 23:56   ` Paul E. McKenney
2015-02-06 18:01   ` Frederic Weisbecker [this message]
2015-02-06 23:24   ` Frederic Weisbecker
2015-02-05 20:23 ` [PATCH 5/5] nohz: add stub context_tracking_is_enabled riel
2015-02-05 23:56   ` Paul E. McKenney
2015-02-06 13:46 ` [PATCH v2 0/5] rcu,nohz,kvm: use RCU extended quiescent state when running KVM guest Frederic Weisbecker
2015-02-06 13:50   ` Paolo Bonzini
2015-02-06 16:19     ` Paul E. McKenney
2015-02-06 18:09     ` Frederic Weisbecker
2015-02-06 14:56   ` Rik van Riel
2015-02-06 18:05     ` Frederic Weisbecker
2015-02-06 15:00 ` Christian Borntraeger
2015-02-06 18:20   ` Frederic Weisbecker

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