diff options
| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2016-11-30 06:24:30 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-06-01 15:15:53 -0700 |
| commit | 1b9d76e44cac9aaa2e7d19fe746252b4b41d8353 (patch) | |
| tree | fea78fc39a35f756844fd1c6434bad0d305b32f9 /kernel/rcu | |
| parent | c3fa663c7c4b86dc42a23cf72607616a6cc4da92 (diff) | |
sched,rcu: Make cond_resched() provide RCU quiescent state
There is some confusion as to which of cond_resched() or
cond_resched_rcu_qs() should be added to long in-kernel loops.
This commit therefore eliminates the decision by adding RCU quiescent
states to cond_resched(). This commit also simplifies the code that
used to interact with cond_resched_rcu_qs(), and that now interacts with
cond_resched(), to reduce its overhead. This reduction is necessary to
allow the heavier-weight cond_resched_rcu_qs() mechanism to be invoked
everywhere that cond_resched() is invoked.
Part of that reduction in overhead converts the jiffies_till_sched_qs
kernel parameter to read-only at runtime, thus eliminating the need for
bounds checking.
Reported-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 23 |
1 files changed, 4 insertions, 19 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 51d4c3acf32d..ab4c2cea208d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -537,8 +537,8 @@ module_param(rcu_kick_kthreads, bool, 0644); * How long the grace period must be before we start recruiting * quiescent-state help from rcu_note_context_switch(). */ -static ulong jiffies_till_sched_qs = HZ / 20; -module_param(jiffies_till_sched_qs, ulong, 0644); +static ulong jiffies_till_sched_qs = HZ / 16; +module_param(jiffies_till_sched_qs, ulong, 0444); static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp); @@ -1230,7 +1230,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) unsigned long jtsq; bool *rnhqp; bool *ruqp; - unsigned long rjtsc; struct rcu_node *rnp; /* @@ -1247,23 +1246,13 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return 1; } - /* Compute and saturate jiffies_till_sched_qs. */ - jtsq = jiffies_till_sched_qs; - rjtsc = rcu_jiffies_till_stall_check(); - if (jtsq > rjtsc / 2) { - WRITE_ONCE(jiffies_till_sched_qs, rjtsc); - jtsq = rjtsc / 2; - } else if (jtsq < 1) { - WRITE_ONCE(jiffies_till_sched_qs, 1); - jtsq = 1; - } - /* * Has this CPU encountered a cond_resched_rcu_qs() since the * beginning of the grace period? For this to be the case, * the CPU has to have noticed the current grace period. This * might not be the case for nohz_full CPUs looping in the kernel. */ + jtsq = jiffies_till_sched_qs; rnp = rdp->mynode; ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu); if (time_after(jiffies, rdp->rsp->gp_start + jtsq) && @@ -1271,7 +1260,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc")); return 1; - } else { + } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) { /* Load rcu_qs_ctr before store to rcu_urgent_qs. */ smp_store_release(ruqp, true); } @@ -1299,10 +1288,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) * updates are only once every few jiffies, the probability of * lossage (and thus of slight grace-period extension) is * quite low. - * - * Note that if the jiffies_till_sched_qs boot/sysfs parameter - * is set too high, we override with half of the RCU CPU stall - * warning delay. */ rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu); if (!READ_ONCE(*rnhqp) && |