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rcu: Kick CPU halfway to RCU CPU stall warning 

When an RCU CPU stall warning occurs, the CPU invokes resched_cpu() on
itself.  This can help move the grace period forward in some situations,
but it would be even better to do this -before- the RCU CPU stall warning.
This commit therefore causes resched_cpu() to be called every five jiffies
once the system is halfway to an RCU CPU stall warning.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2013-09-23 13:57:18 -07:00
parent dc1ccc4815
commit 6193c76aba
2 changed files with 27 additions and 1 deletions
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26
kernel/rcu/tree.c
View File

@ -754,6 +754,12 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp,
return (rdp->dynticks_snap & 0x1) == 0;
}
/*
* This function really isn't for public consumption, but RCU is special in
* that context switches can allow the state machine to make progress.
*/
extern void resched_cpu(int cpu);
/*
* Return true if the specified CPU has passed through a quiescent
* state by virtue of being in or having passed through an dynticks
@ -812,16 +818,34 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
*/
rcu_kick_nohz_cpu(rdp->cpu);
/*
* Alternatively, the CPU might be running in the kernel
* for an extended period of time without a quiescent state.
* Attempt to force the CPU through the scheduler to gain the
* needed quiescent state, but only if the grace period has gone
* on for an uncommonly long time. If there are many stuck CPUs,
* we will beat on the first one until it gets unstuck, then move
* to the next. Only do this for the primary flavor of RCU.
*/
if (rdp->rsp == rcu_state &&
ULONG_CMP_GE(ACCESS_ONCE(jiffies), rdp->rsp->jiffies_resched)) {
rdp->rsp->jiffies_resched += 5;
resched_cpu(rdp->cpu);
}
return 0;
}
static void record_gp_stall_check_time(struct rcu_state *rsp)
{
unsigned long j = ACCESS_ONCE(jiffies);
unsigned long j1;
rsp->gp_start = j;
smp_wmb(); /* Record start time before stall time. */
rsp->jiffies_stall = j + rcu_jiffies_till_stall_check();
j1 = rcu_jiffies_till_stall_check();
rsp->jiffies_stall = j + j1;
rsp->jiffies_resched = j + j1 / 2;
}
/*

2
kernel/rcu/tree.h
View File

@ -453,6 +453,8 @@ struct rcu_state {
/* but in jiffies. */
unsigned long jiffies_stall; /* Time at which to check */
/* for CPU stalls. */
unsigned long jiffies_resched; /* Time at which to resched */
/* a reluctant CPU. */
unsigned long gp_max; /* Maximum GP duration in */
/* jiffies. */
const char *name; /* Name of structure. */