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rcu/nocb: Update comments to prepare for forward-progress work

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This commit simply rewords comments to prepare for leader nocb kthreads
doing only grace-period work and callback shuffling.  This will mean
the addition of replacement kthreads to invoke callbacks.  The "leader"
and "follower" thus become less meaningful, so the commit changes no-CB
comments with these strings to "GP" and "CB", respectively.  (Give or
take the usual grammatical transformations.)

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-03-28 15:44:18 -07:00
parent 58bf6f77c6
commit 6484fe54b5
2 changed files with 33 additions and 32 deletions
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8
kernel/rcu/tree.h
View file

@ -206,17 +206,17 @@ struct rcu_data {
int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */
struct timer_list nocb_timer; /* Enforce finite deferral. */
/* The following fields are used by the leader, hence own cacheline. */
/* The following fields are used by GP kthread, hence own cacheline. */
struct rcu_head *nocb_gp_head ____cacheline_internodealigned_in_smp;
/* CBs waiting for GP. */
struct rcu_head **nocb_gp_tail;
bool nocb_gp_sleep; /* Is the nocb leader thread asleep? */
bool nocb_gp_sleep; /* Is the nocb GP thread asleep? */
struct rcu_data *nocb_next_cb_rdp;
/* Next rcu_data in wakeup chain. */
/* The following fields are used by the follower, hence new cachline. */
/* The following fields are used by CB kthread, hence new cachline. */
struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp;
/* Leader CPU takes GP-end wakeups. */
/* GP rdp takes GP-end wakeups. */
#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
/* 6) RCU priority boosting. */

57
kernel/rcu/tree_plugin.h
View file

@ -1447,10 +1447,10 @@ static void rcu_cleanup_after_idle(void)
* specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
* created that pull the callbacks from the corresponding CPU, wait for
* a grace period to elapse, and invoke the callbacks. These kthreads
* are organized into leaders, which manage incoming callbacks, wait for
* grace periods, and awaken followers, and the followers, which only
* invoke callbacks. Each leader is its own follower. The no-CBs CPUs
* do a wake_up() on their kthread when they insert a callback into any
* are organized into GP kthreads, which manage incoming callbacks, wait for
* grace periods, and awaken CB kthreads, and the CB kthreads, which only
* invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
* do a wake_up() on their GP kthread when they insert a callback into any
* empty list, unless the rcu_nocb_poll boot parameter has been specified,
* in which case each kthread actively polls its CPU. (Which isn't so great
* for energy efficiency, but which does reduce RCU's overhead on that CPU.)
@ -1521,7 +1521,7 @@ bool rcu_is_nocb_cpu(int cpu)
}
/*
* Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
* Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
* and this function releases it.
*/
static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
@ -1548,7 +1548,7 @@ static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
}
/*
* Kick the leader kthread for this NOCB group, but caller has not
* Kick the GP kthread for this NOCB group, but caller has not
* acquired locks.
*/
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
@ -1560,8 +1560,8 @@ static void wake_nocb_leader(struct rcu_data *rdp, bool force)
}
/*
* Arrange to wake the leader kthread for this NOCB group at some
* future time when it is safe to do so.
* Arrange to wake the GP kthread for this NOCB group at some future
* time when it is safe to do so.
*/
static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
const char *reason)
@ -1783,7 +1783,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
}
/*
* Leaders come here to wait for additional callbacks to show up.
* No-CBs GP kthreads come here to wait for additional callbacks to show up.
* This function does not return until callbacks appear.
*/
static void nocb_leader_wait(struct rcu_data *my_rdp)
@ -1812,8 +1812,8 @@ static void nocb_leader_wait(struct rcu_data *my_rdp)
}
/*
* Each pass through the following loop checks a follower for CBs.
* We are our own first follower. Any CBs found are moved to
* Each pass through the following loop checks for CBs.
* We are our own first CB kthread. Any CBs found are moved to
* nocb_gp_head, where they await a grace period.
*/
gotcbs = false;
@ -1821,7 +1821,7 @@ static void nocb_leader_wait(struct rcu_data *my_rdp)
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
if (!rdp->nocb_gp_head)
continue; /* No CBs here, try next follower. */
continue; /* No CBs here, try next. */
/* Move callbacks to wait-for-GP list, which is empty. */
WRITE_ONCE(rdp->nocb_head, NULL);
@ -1844,7 +1844,7 @@ static void nocb_leader_wait(struct rcu_data *my_rdp)
/* Wait for one grace period. */
rcu_nocb_wait_gp(my_rdp);
/* Each pass through the following loop wakes a follower, if needed. */
/* Each pass through this loop wakes a CB kthread, if needed. */
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
if (!rcu_nocb_poll &&
READ_ONCE(rdp->nocb_head) &&
@ -1854,27 +1854,27 @@ static void nocb_leader_wait(struct rcu_data *my_rdp)
raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
}
if (!rdp->nocb_gp_head)
continue; /* No CBs, so no need to wake follower. */
continue; /* No CBs, so no need to wake kthread. */
/* Append callbacks to follower's "done" list. */
/* Append callbacks to CB kthread's "done" list. */
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
tail = rdp->nocb_cb_tail;
rdp->nocb_cb_tail = rdp->nocb_gp_tail;
*tail = rdp->nocb_gp_head;
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
if (rdp != my_rdp && tail == &rdp->nocb_cb_head) {
/* List was empty, so wake up the follower. */
/* List was empty, so wake up the kthread. */
swake_up_one(&rdp->nocb_wq);
}
}
/* If we (the leader) don't have CBs, go wait some more. */
/* If we (the GP kthreads) don't have CBs, go wait some more. */
if (!my_rdp->nocb_cb_head)
goto wait_again;
}
/*
* Followers come here to wait for additional callbacks to show up.
* No-CBs CB kthreads come here to wait for additional callbacks to show up.
* This function does not return until callbacks appear.
*/
static void nocb_follower_wait(struct rcu_data *rdp)
@ -1894,9 +1894,10 @@ static void nocb_follower_wait(struct rcu_data *rdp)
/*
* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
* callbacks queued by the corresponding no-CBs CPU, however, there is
* an optional leader-follower relationship so that the grace-period
* kthreads don't have to do quite so many wakeups.
* callbacks queued by the corresponding no-CBs CPU, however, there is an
* optional GP-CB relationship so that the grace-period kthreads don't
* have to do quite so many wakeups (as in they only need to wake the
* no-CBs GP kthreads, not the CB kthreads).
*/
static int rcu_nocb_kthread(void *arg)
{
@ -2056,7 +2057,7 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
/*
* If the specified CPU is a no-CBs CPU that does not already have its
* rcuo kthread, spawn it. If the CPUs are brought online out of order,
* this can require re-organizing the leader-follower relationships.
* this can require re-organizing the GP-CB relationships.
*/
static void rcu_spawn_one_nocb_kthread(int cpu)
{
@ -2073,7 +2074,7 @@ static void rcu_spawn_one_nocb_kthread(int cpu)
if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_cb_kthread)
return;
/* If we didn't spawn the leader first, reorganize! */
/* If we didn't spawn the GP kthread first, reorganize! */
rdp_old_leader = rdp_spawn->nocb_gp_rdp;
if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_cb_kthread) {
rdp_last = NULL;
@ -2125,18 +2126,18 @@ static void __init rcu_spawn_nocb_kthreads(void)
rcu_spawn_cpu_nocb_kthread(cpu);
}
/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
static int rcu_nocb_leader_stride = -1;
module_param(rcu_nocb_leader_stride, int, 0444);
/*
* Initialize leader-follower relationships for all no-CBs CPU.
* Initialize GP-CB relationships for all no-CBs CPU.
*/
static void __init rcu_organize_nocb_kthreads(void)
{
int cpu;
int ls = rcu_nocb_leader_stride;
int nl = 0; /* Next leader. */
int nl = 0; /* Next GP kthread. */
struct rcu_data *rdp;
struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
struct rcu_data *rdp_prev = NULL;
@ -2156,12 +2157,12 @@ static void __init rcu_organize_nocb_kthreads(void)
for_each_cpu(cpu, rcu_nocb_mask) {
rdp = per_cpu_ptr(&rcu_data, cpu);
if (rdp->cpu >= nl) {
/* New leader, set up for followers & next leader. */
/* New GP kthread, set up for CBs & next GP. */
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
rdp->nocb_gp_rdp = rdp;
rdp_leader = rdp;
} else {
/* Another follower, link to previous leader. */
/* Another CB kthread, link to previous GP kthread. */
rdp->nocb_gp_rdp = rdp_leader;
rdp_prev->nocb_next_cb_rdp = rdp;
}