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rcu: Update cpu_needs_another_gp() for futures from non-NOCB CPUs 

In the old days, the only source of requests for future grace periods
was NOCB CPUs.  This has changed: CPUs routinely post requests for
future grace periods in order to promote power efficiency and reduce
OS jitter with minimal impact on grace-period latency.  This commit
therefore updates cpu_needs_another_gp() to invoke rcu_future_needs_gp()
instead of rcu_nocb_needs_gp().  The latter is no longer used, so is
now removed.  This commit also adds tracing for the irq_work_queue()
wakeup case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Paul E. McKenney 2014-03-10 10:55:52 -07:00
parent 83ebe63ead
commit 365187fbc0
3 changed files with 29 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
kernel/rcu/tree.c
View File

@ -323,6 +323,28 @@ cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
rdp->nxttail[RCU_DONE_TAIL] != NULL;
}
/*
* Return the root node of the specified rcu_state structure.
*/
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
return &rsp->node[0];
}
/*
* Is there any need for future grace periods?
* Interrupts must be disabled. If the caller does not hold the root
* rnp_node structure's ->lock, the results are advisory only.
*/
static int rcu_future_needs_gp(struct rcu_state *rsp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
int idx = (ACCESS_ONCE(rnp->completed) + 1) & 0x1;
int *fp = &rnp->need_future_gp[idx];
return ACCESS_ONCE(*fp);
}
/*
* Does the current CPU require a not-yet-started grace period?
* The caller must have disabled interrupts to prevent races with
@ -335,7 +357,7 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
if (rcu_gp_in_progress(rsp))
return 0; /* No, a grace period is already in progress. */
if (rcu_nocb_needs_gp(rsp))
if (rcu_future_needs_gp(rsp))
return 1; /* Yes, a no-CBs CPU needs one. */
if (!rdp->nxttail[RCU_NEXT_TAIL])
return 0; /* No, this is a no-CBs (or offline) CPU. */
@ -349,14 +371,6 @@ cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
return 0; /* No grace period needed. */
}
/*
* Return the root node of the specified rcu_state structure.
*/
static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
{
return &rsp->node[0];
}
/*
* rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
*
@ -1672,6 +1686,8 @@ static void rsp_wakeup(struct irq_work *work)
/* Wake up rcu_gp_kthread() to start the grace period. */
wake_up(&rsp->gp_wq);
trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
"Workqueuewoken");
}
/*
@ -1706,9 +1722,12 @@ rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
* the wakeup to interrupt context. And don't bother waking
* up the running kthread.
*/
if (current != rsp->gp_kthread)
if (current != rsp->gp_kthread) {
trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
"Workqueuewake");
irq_work_queue(&rsp->wakeup_work);
}
}
/*
* Similar to rcu_start_gp_advanced(), but also advance the calling CPU's

1
kernel/rcu/tree.h
View File

@ -547,7 +547,6 @@ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu);
static void print_cpu_stall_info_end(void);
static void zero_cpu_stall_ticks(struct rcu_data *rdp);
static void increment_cpu_stall_ticks(void);
static int rcu_nocb_needs_gp(struct rcu_state *rsp);
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq);
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp);
static void rcu_init_one_nocb(struct rcu_node *rnp);

18
kernel/rcu/tree_plugin.h
View File

@ -2067,19 +2067,6 @@ static int __init parse_rcu_nocb_poll(char *arg)
}
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
/*
* Do any no-CBs CPUs need another grace period?
*
* Interrupts must be disabled. If the caller does not hold the root
* rnp_node structure's ->lock, the results are advisory only.
*/
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
{
struct rcu_node *rnp = rcu_get_root(rsp);
return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
}
/*
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
* grace period.
@ -2402,11 +2389,6 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
{
return 0;
}
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
{
}