On Thu, Aug 30, 2012 at 11:18:28AM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paul.mcken...@linaro.org>
>
> Some uses of RCU benefit from shorter grace periods, while others benefit
> more from the greater efficiency provided by longer grace periods.
> Therefore, this commit allows the durations to be controlled from sysfs.
> There are two sysfs parameters, one named "jiffies_till_first_fqs" that
> specifies the delay in jiffies from the end of grace-period initialization
> until the first attempt to force quiescent states, and the other named
> "jiffies_till_next_fqs" that specifies the delay (again in jiffies)
> between subsequent attempts to force quiescent states. They both default
> to three jiffies, which is compatible with the old hard-coded behavior.
>
> Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Signed-off-by: Josh Triplett <j...@joshtriplett.org>
> Documentation/kernel-parameters.txt | 11 +++++++++++
> kernel/rcutree.c | 25 ++++++++++++++++++++++---
> 2 files changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index ad7e2e5..55ada04 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2385,6 +2385,17 @@ bytes respectively. Such letter suffixes can also be
> entirely omitted.
> rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
> Set timeout for RCU CPU stall warning messages.
>
> + rcutree.jiffies_till_first_fqs= [KNL,BOOT]
> + Set delay from grace-period initialization to
> + first attempt to force quiescent states.
> + Units are jiffies, minimum value is zero,
> + and maximum value is HZ.
> +
> + rcutree.jiffies_till_next_fqs= [KNL,BOOT]
> + Set delay between subsequent attempts to force
> + quiescent states. Units are jiffies, minimum
> + value is one, and maximum value is HZ.
> +
> rcutorture.fqs_duration= [KNL,BOOT]
> Set duration of force_quiescent_state bursts.
>
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index ed1be62..1d33240 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -226,6 +226,12 @@ int rcu_cpu_stall_timeout __read_mostly =
> CONFIG_RCU_CPU_STALL_TIMEOUT;
> module_param(rcu_cpu_stall_suppress, int, 0644);
> module_param(rcu_cpu_stall_timeout, int, 0644);
>
> +static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS;
> +static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS;
> +
> +module_param(jiffies_till_first_fqs, ulong, 0644);
> +module_param(jiffies_till_next_fqs, ulong, 0644);
> +
> static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *));
> static void force_quiescent_state(struct rcu_state *rsp);
> static int rcu_pending(int cpu);
> @@ -1193,6 +1199,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> static int rcu_gp_kthread(void *arg)
> {
> int fqs_state;
> + unsigned long j;
> int ret;
> struct rcu_state *rsp = arg;
> struct rcu_node *rnp = rcu_get_root(rsp);
> @@ -1213,14 +1220,18 @@ static int rcu_gp_kthread(void *arg)
>
> /* Handle quiescent-state forcing. */
> fqs_state = RCU_SAVE_DYNTICK;
> + j = jiffies_till_first_fqs;
> + if (j > HZ) {
> + j = HZ;
> + jiffies_till_first_fqs = HZ;
> + }
> for (;;) {
> - rsp->jiffies_force_qs = jiffies +
> - RCU_JIFFIES_TILL_FORCE_QS;
> + rsp->jiffies_force_qs = jiffies + j;
> ret = wait_event_interruptible_timeout(rsp->gp_wq,
> (rsp->gp_flags & RCU_GP_FLAG_FQS) ||
> (!ACCESS_ONCE(rnp->qsmask) &&
> !rcu_preempt_blocked_readers_cgp(rnp)),
> - RCU_JIFFIES_TILL_FORCE_QS);
> + j);
> /* If grace period done, leave loop. */
> if (!ACCESS_ONCE(rnp->qsmask) &&
> !rcu_preempt_blocked_readers_cgp(rnp))
> @@ -1234,6 +1245,14 @@ static int rcu_gp_kthread(void *arg)
> cond_resched();
> flush_signals(current);
> }
> + j = jiffies_till_next_fqs;
> + if (j > HZ) {
> + j = HZ;
> + jiffies_till_next_fqs = HZ;
> + } else if (j < 1) {
> + j = 1;
> + jiffies_till_next_fqs = 1;
> + }
> }
>
> /* Handle grace-period end. */
> --
> 1.7.8
>
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