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Message-ID: <20140902205828.GN5001@linux.vnet.ibm.com>
Date: Tue, 2 Sep 2014 13:58:28 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Christoph Lameter <cl@...ux.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
linux-kernel@...r.kernel.org
Subject: Re: rcu: Remove rcu_dynticks * parameters when they are always
this_cpu_ptr(&rcu_dynticks)
On Tue, Sep 02, 2014 at 03:13:44PM -0500, Christoph Lameter wrote:
> For some functions in kernel/rcu/tree* the rdtp parameter is always this_cpu_ptr(rdtp).
> Remove the parameter if constant and calculate the pointer in function.
>
> This will have the advantage that it is obvious that the address are all per cpu
> offsets and thus it will enable the use of this_cpu_ops in the future.
>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
Looks plausible, thank you. Let's see what testing, especially
Fengguang's testing, makes of this. ;-)
Thanx, Paul
> Index: linux/kernel/rcu/tree.c
> ===================================================================
> --- linux.orig/kernel/rcu/tree.c
> +++ linux/kernel/rcu/tree.c
> @@ -499,11 +499,11 @@ cpu_needs_another_gp(struct rcu_state *r
> * we really have entered idle, and must do the appropriate accounting.
> * The caller must have disabled interrupts.
> */
> -static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
> - bool user)
> +static void rcu_eqs_enter_common(long long oldval, bool user)
> {
> struct rcu_state *rsp;
> struct rcu_data *rdp;
> + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
>
> trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
> if (!user && !is_idle_task(current)) {
> @@ -553,7 +553,7 @@ static void rcu_eqs_enter(bool user)
> WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
> if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
> rdtp->dynticks_nesting = 0;
> - rcu_eqs_enter_common(rdtp, oldval, user);
> + rcu_eqs_enter_common(oldval, user);
> } else {
> rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
> }
> @@ -577,7 +577,7 @@ void rcu_idle_enter(void)
>
> local_irq_save(flags);
> rcu_eqs_enter(false);
> - rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
> + rcu_sysidle_enter(0);
> local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_idle_enter);
> @@ -627,8 +627,8 @@ void rcu_irq_exit(void)
> if (rdtp->dynticks_nesting)
> trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
> else
> - rcu_eqs_enter_common(rdtp, oldval, true);
> - rcu_sysidle_enter(rdtp, 1);
> + rcu_eqs_enter_common(oldval, true);
> + rcu_sysidle_enter(1);
> local_irq_restore(flags);
> }
>
> @@ -639,9 +639,11 @@ void rcu_irq_exit(void)
> * we really have exited idle, and must do the appropriate accounting.
> * The caller must have disabled interrupts.
> */
> -static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
> +static void rcu_eqs_exit_common(long long oldval,
> int user)
> {
> + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
> +
> smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */
> atomic_inc(&rdtp->dynticks);
> /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
> @@ -678,7 +680,7 @@ static void rcu_eqs_exit(bool user)
> rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
> } else {
> rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
> - rcu_eqs_exit_common(rdtp, oldval, user);
> + rcu_eqs_exit_common(oldval, user);
> }
> }
>
> @@ -699,7 +701,7 @@ void rcu_idle_exit(void)
>
> local_irq_save(flags);
> rcu_eqs_exit(false);
> - rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
> + rcu_sysidle_exit(0);
> local_irq_restore(flags);
> }
> EXPORT_SYMBOL_GPL(rcu_idle_exit);
> @@ -750,8 +752,8 @@ void rcu_irq_enter(void)
> if (oldval)
> trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
> else
> - rcu_eqs_exit_common(rdtp, oldval, true);
> - rcu_sysidle_exit(rdtp, 1);
> + rcu_eqs_exit_common(oldval, true);
> + rcu_sysidle_exit(1);
> local_irq_restore(flags);
> }
>
> Index: linux/kernel/rcu/tree.h
> ===================================================================
> --- linux.orig/kernel/rcu/tree.h
> +++ linux/kernel/rcu/tree.h
> @@ -595,8 +595,8 @@ static void rcu_boot_init_nocb_percpu_da
> static void rcu_spawn_nocb_kthreads(struct rcu_state *rsp);
> static void __maybe_unused rcu_kick_nohz_cpu(int cpu);
> static bool init_nocb_callback_list(struct rcu_data *rdp);
> -static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq);
> -static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq);
> +static void rcu_sysidle_enter(int irq);
> +static void rcu_sysidle_exit(int irq);
> static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
> unsigned long *maxj);
> static bool is_sysidle_rcu_state(struct rcu_state *rsp);
> Index: linux/kernel/rcu/tree_plugin.h
> ===================================================================
> --- linux.orig/kernel/rcu/tree_plugin.h
> +++ linux/kernel/rcu/tree_plugin.h
> @@ -2618,9 +2618,10 @@ static int full_sysidle_state; /* Curre
> * to detect full-system idle states, not RCU quiescent states and grace
> * periods. The caller must have disabled interrupts.
> */
> -static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
> +static void rcu_sysidle_enter(int irq)
> {
> unsigned long j;
> + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
>
> /* Adjust nesting, check for fully idle. */
> if (irq) {
> @@ -2685,8 +2686,9 @@ void rcu_sysidle_force_exit(void)
> * usermode execution does -not- count as idle here! The caller must
> * have disabled interrupts.
> */
> -static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
> +static void rcu_sysidle_exit(int irq)
> {
> + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
> /* Adjust nesting, check for already non-idle. */
> if (irq) {
> rdtp->dynticks_idle_nesting++;
> @@ -2968,11 +2970,11 @@ static void rcu_sysidle_init_percpu_data
>
> #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
>
> -static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
> +static void rcu_sysidle_enter(int irq)
> {
> }
>
> -static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
> +static void rcu_sysidle_exit(int irq)
> {
> }
>
--
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