Messages in this thread | | | Date | Mon, 3 Sep 2012 02:30:16 -0700 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 13/23] rcu: Control grace-period duration from sysfs |
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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>
> 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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