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SubjectRe: [PATCH tip/core/rcu 13/23] rcu: Control grace-period duration from sysfs
On Mon, Sep 03, 2012 at 02:30:16AM -0700, Josh Triplett wrote:
> On Thu, Aug 30, 2012 at 11:18:28AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul.mckenney@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.mckenney@linaro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> Signed-off-by: Josh Triplett <josh@joshtriplett.org>

Er, sorry, typo:
Reviewed-by: Josh Triplett <josh@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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