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SubjectRe: [this_cpu_xx 11/11] RCU: Use this_cpu operations
On Fri, Jun 05, 2009 at 03:18:30PM -0400, cl@linux-foundation.org wrote:
> RCU does not do dynamic allocations but it increments per cpu variables
> a lot. These instructions results in a move to a register and then back
> to memory. This patch will make it use the inc/dec instructions on x86
> that do not need a register.

Looks good to me!

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

> Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
>
> ---
> kernel/rcupreempt.c | 4 ++--
> kernel/rcutorture.c | 8 ++++----
> 2 files changed, 6 insertions(+), 6 deletions(-)
>
> Index: linux-2.6/kernel/rcutorture.c
> ===================================================================
> --- linux-2.6.orig/kernel/rcutorture.c 2009-06-04 14:26:42.000000000 -0500
> +++ linux-2.6/kernel/rcutorture.c 2009-06-04 14:38:05.000000000 -0500
> @@ -709,13 +709,13 @@ static void rcu_torture_timer(unsigned l
> /* Should not happen, but... */
> pipe_count = RCU_TORTURE_PIPE_LEN;
> }
> - ++__get_cpu_var(rcu_torture_count)[pipe_count];
> + __this_cpu_inc(per_cpu_var(rcu_torture_count)[pipe_count]);
> completed = cur_ops->completed() - completed;
> if (completed > RCU_TORTURE_PIPE_LEN) {
> /* Should not happen, but... */
> completed = RCU_TORTURE_PIPE_LEN;
> }
> - ++__get_cpu_var(rcu_torture_batch)[completed];
> + __this_cpu_inc(per_cpu_var(rcu_torture_batch)[completed]);
> preempt_enable();
> cur_ops->readunlock(idx);
> }
> @@ -764,13 +764,13 @@ rcu_torture_reader(void *arg)
> /* Should not happen, but... */
> pipe_count = RCU_TORTURE_PIPE_LEN;
> }
> - ++__get_cpu_var(rcu_torture_count)[pipe_count];
> + __this_cpu_inc(per_cpu_var(rcu_torture_count)[pipe_count]);
> completed = cur_ops->completed() - completed;
> if (completed > RCU_TORTURE_PIPE_LEN) {
> /* Should not happen, but... */
> completed = RCU_TORTURE_PIPE_LEN;
> }
> - ++__get_cpu_var(rcu_torture_batch)[completed];
> + __this_cpu_inc(per_cpu_var(rcu_torture_batch)[completed]);
> preempt_enable();
> cur_ops->readunlock(idx);
> schedule();
> Index: linux-2.6/kernel/rcupreempt.c
> ===================================================================
> --- linux-2.6.orig/kernel/rcupreempt.c 2009-06-04 14:28:53.000000000 -0500
> +++ linux-2.6/kernel/rcupreempt.c 2009-06-04 14:39:35.000000000 -0500
> @@ -173,7 +173,7 @@ void rcu_enter_nohz(void)
> static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
>
> smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
> - __get_cpu_var(rcu_dyntick_sched).dynticks++;
> + __this_cpu_inc(per_cpu_var(rcu_dyntick_sched).dynticks);
> WARN_ON_RATELIMIT(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1, &rs);
> }
>
> @@ -181,7 +181,7 @@ void rcu_exit_nohz(void)
> {
> static DEFINE_RATELIMIT_STATE(rs, 10 * HZ, 1);
>
> - __get_cpu_var(rcu_dyntick_sched).dynticks++;
> + __this_cpu_inc(per_cpu_var(rcu_dyntick_sched).dynticks);
> smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
> WARN_ON_RATELIMIT(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1),
> &rs);
>
> --
> --
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