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rcu: Remove kfree_rcu() special casing and lazy-callback handling

Browse Source 
This commit removes kfree_rcu() special-casing and the lazy-callback
handling from Tree RCU.  It moves some of this special casing to Tiny RCU,
the removal of which will be the subject of later commits.

This results in a nice negative delta.

Suggested-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Add slab.h #include, thanks to kbuild test robot <lkp@intel.com>. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2019-08-30 12:36:32 -04:00 committed by Paul E. McKenney
parent e99637becb
commit 77a40f9703
12 changed files with 90 additions and 159 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
Documentation/RCU/stallwarn.txt
View File

@ -225,18 +225,13 @@ an estimate of the total number of RCU callbacks queued across all CPUs
In kernels with CONFIG_RCU_FAST_NO_HZ, more information is printed
for each CPU:
0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 Nonlazy posted: ..D
0: (64628 ticks this GP) idle=dd5/3fffffffffffffff/0 softirq=82/543 last_accelerate: a345/d342 dyntick_enabled: 1
The "last_accelerate:" prints the low-order 16 bits (in hex) of the
jiffies counter when this CPU last invoked rcu_try_advance_all_cbs()
from rcu_needs_cpu() or last invoked rcu_accelerate_cbs() from
rcu_prepare_for_idle(). The "Nonlazy posted:" indicates lazy-callback
status, so that an "l" indicates that all callbacks were lazy at the start
of the last idle period and an "L" indicates that there are currently
no non-lazy callbacks (in both cases, "." is printed otherwise, as
shown above) and "D" indicates that dyntick-idle processing is enabled
("." is printed otherwise, for example, if disabled via the "nohz="
kernel boot parameter).
rcu_prepare_for_idle(). "dyntick_enabled: 1" indicates that dyntick-idle
processing is enabled.
If the grace period ends just as the stall warning starts printing,
there will be a spurious stall-warning message, which will include

2
include/linux/rcu_segcblist.h
View File

@ -22,7 +22,6 @@ struct rcu_cblist {
struct rcu_head *head;
struct rcu_head **tail;
long len;
long len_lazy;
};
#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
@ -73,7 +72,6 @@ struct rcu_segcblist {
#else
long len;
#endif
long len_lazy;
u8 enabled;
u8 offloaded;
};

32
include/trace/events/rcu.h
View File

@ -481,16 +481,14 @@ TRACE_EVENT_RCU(rcu_dyntick,
*/
TRACE_EVENT_RCU(rcu_callback,
TP_PROTO(const char *rcuname, struct rcu_head *rhp, long qlen_lazy,
long qlen),
TP_PROTO(const char *rcuname, struct rcu_head *rhp, long qlen),
TP_ARGS(rcuname, rhp, qlen_lazy, qlen),
TP_ARGS(rcuname, rhp, qlen),
TP_STRUCT__entry(
__field(const char *, rcuname)
__field(void *, rhp)
__field(void *, func)
__field(long, qlen_lazy)
__field(long, qlen)
),
@ -498,13 +496,12 @@ TRACE_EVENT_RCU(rcu_callback,
__entry->rcuname = rcuname;
__entry->rhp = rhp;
__entry->func = rhp->func;
__entry->qlen_lazy = qlen_lazy;
__entry->qlen = qlen;
),
TP_printk("%s rhp=%p func=%ps %ld/%ld",
TP_printk("%s rhp=%p func=%ps %ld",
__entry->rcuname, __entry->rhp, __entry->func,
__entry->qlen_lazy, __entry->qlen)
__entry->qlen)
);
/*
@ -518,15 +515,14 @@ TRACE_EVENT_RCU(rcu_callback,
TRACE_EVENT_RCU(rcu_kfree_callback,
TP_PROTO(const char *rcuname, struct rcu_head *rhp, unsigned long offset,
long qlen_lazy, long qlen),
long qlen),
TP_ARGS(rcuname, rhp, offset, qlen_lazy, qlen),
TP_ARGS(rcuname, rhp, offset, qlen),
TP_STRUCT__entry(
__field(const char *, rcuname)
__field(void *, rhp)
__field(unsigned long, offset)
__field(long, qlen_lazy)
__field(long, qlen)
),
@ -534,13 +530,12 @@ TRACE_EVENT_RCU(rcu_kfree_callback,
__entry->rcuname = rcuname;
__entry->rhp = rhp;
__entry->offset = offset;
__entry->qlen_lazy = qlen_lazy;
__entry->qlen = qlen;
),
TP_printk("%s rhp=%p func=%ld %ld/%ld",
TP_printk("%s rhp=%p func=%ld %ld",
__entry->rcuname, __entry->rhp, __entry->offset,
__entry->qlen_lazy, __entry->qlen)
__entry->qlen)
);
/*
@ -552,27 +547,24 @@ TRACE_EVENT_RCU(rcu_kfree_callback,
*/
TRACE_EVENT_RCU(rcu_batch_start,
TP_PROTO(const char *rcuname, long qlen_lazy, long qlen, long blimit),
TP_PROTO(const char *rcuname, long qlen, long blimit),
TP_ARGS(rcuname, qlen_lazy, qlen, blimit),
TP_ARGS(rcuname, qlen, blimit),
TP_STRUCT__entry(
__field(const char *, rcuname)
__field(long, qlen_lazy)
__field(long, qlen)
__field(long, blimit)
),
TP_fast_assign(
__entry->rcuname = rcuname;
__entry->qlen_lazy = qlen_lazy;
__entry->qlen = qlen;
__entry->blimit = blimit;
),
TP_printk("%s CBs=%ld/%ld bl=%ld",
__entry->rcuname, __entry->qlen_lazy, __entry->qlen,
__entry->blimit)
TP_printk("%s CBs=%ld bl=%ld",
__entry->rcuname, __entry->qlen, __entry->blimit)
);
/*

27
kernel/rcu/rcu.h
View File

@ -198,33 +198,6 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
void kfree(const void *);
/*
* Reclaim the specified callback, either by invoking it (non-lazy case)
* or freeing it directly (lazy case). Return true if lazy, false otherwise.
*/
static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
{
rcu_callback_t f;
unsigned long offset = (unsigned long)head->func;
rcu_lock_acquire(&rcu_callback_map);
if (__is_kfree_rcu_offset(offset)) {
trace_rcu_invoke_kfree_callback(rn, head, offset);
kfree((void *)head - offset);
rcu_lock_release(&rcu_callback_map);
return true;
} else {
trace_rcu_invoke_callback(rn, head);
f = head->func;
WRITE_ONCE(head->func, (rcu_callback_t)0L);
f(head);
rcu_lock_release(&rcu_callback_map);
return false;
}
}
#ifdef CONFIG_RCU_STALL_COMMON
extern int rcu_cpu_stall_ftrace_dump;

25
kernel/rcu/rcu_segcblist.c
View File

@ -20,14 +20,10 @@ void rcu_cblist_init(struct rcu_cblist *rclp)
rclp->head = NULL;
rclp->tail = &rclp->head;
rclp->len = 0;
rclp->len_lazy = 0;
}
/*
* Enqueue an rcu_head structure onto the specified callback list.
* This function assumes that the callback is non-lazy because it
* is intended for use by no-CBs CPUs, which do not distinguish
* between lazy and non-lazy RCU callbacks.
*/
void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp)
{
@ -54,7 +50,6 @@ void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
else
drclp->tail = &drclp->head;
drclp->len = srclp->len;
drclp->len_lazy = srclp->len_lazy;
if (!rhp) {
rcu_cblist_init(srclp);
} else {
@ -62,16 +57,12 @@ void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
srclp->head = rhp;
srclp->tail = &rhp->next;
WRITE_ONCE(srclp->len, 1);
srclp->len_lazy = 0;
}
}
/*
* Dequeue the oldest rcu_head structure from the specified callback
* list. This function assumes that the callback is non-lazy, but
* the caller can later invoke rcu_cblist_dequeued_lazy() if it
* finds otherwise (and if it cares about laziness). This allows
* different users to have different ways of determining laziness.
* list.
*/
struct rcu_head *rcu_cblist_dequeue(struct rcu_cblist *rclp)
{
@ -161,7 +152,6 @@ void rcu_segcblist_init(struct rcu_segcblist *rsclp)
for (i = 0; i < RCU_CBLIST_NSEGS; i++)
rsclp->tails[i] = &rsclp->head;
rcu_segcblist_set_len(rsclp, 0);
rsclp->len_lazy = 0;
rsclp->enabled = 1;
}
@ -173,7 +163,6 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp)
{
WARN_ON_ONCE(!rcu_segcblist_empty(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp));
WARN_ON_ONCE(rcu_segcblist_n_lazy_cbs(rsclp));
rsclp->enabled = 0;
}
@ -253,11 +242,9 @@ bool rcu_segcblist_nextgp(struct rcu_segcblist *rsclp, unsigned long *lp)
* absolutely not OK for it to ever miss posting a callback.
*/
void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy)
struct rcu_head *rhp)
{
rcu_segcblist_inc_len(rsclp);
if (lazy)
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is enqueued. */
rhp->next = NULL;
WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp);
@ -275,15 +262,13 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
* period. You have been warned.
*/
bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy)
struct rcu_head *rhp)
{
int i;
if (rcu_segcblist_n_cbs(rsclp) == 0)
return false;
rcu_segcblist_inc_len(rsclp);
if (lazy)
rsclp->len_lazy++;
smp_mb(); /* Ensure counts are updated before callback is entrained. */
rhp->next = NULL;
for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--)
@ -307,8 +292,6 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
struct rcu_cblist *rclp)
{
rclp->len_lazy += rsclp->len_lazy;
rsclp->len_lazy = 0;
rclp->len = rcu_segcblist_xchg_len(rsclp, 0);
}
@ -361,9 +344,7 @@ void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp,
void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp,
struct rcu_cblist *rclp)
{
rsclp->len_lazy += rclp->len_lazy;
rcu_segcblist_add_len(rsclp, rclp->len);
rclp->len_lazy = 0;
rclp->len = 0;
}

25
kernel/rcu/rcu_segcblist.h
View File

@ -15,15 +15,6 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp)
return READ_ONCE(rclp->len);
}
/*
* Account for the fact that a previously dequeued callback turned out
* to be marked as lazy.
*/
static inline void rcu_cblist_dequeued_lazy(struct rcu_cblist *rclp)
{
rclp->len_lazy--;
}
void rcu_cblist_init(struct rcu_cblist *rclp);
void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp);
void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp,
@ -59,18 +50,6 @@ static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp)
#endif
}
/* Return number of lazy callbacks in segmented callback list. */
static inline long rcu_segcblist_n_lazy_cbs(struct rcu_segcblist *rsclp)
{
return rsclp->len_lazy;
}
/* Return number of lazy callbacks in segmented callback list. */
static inline long rcu_segcblist_n_nonlazy_cbs(struct rcu_segcblist *rsclp)
{
return rcu_segcblist_n_cbs(rsclp) - rsclp->len_lazy;
}
/*
* Is the specified rcu_segcblist enabled, for example, not corresponding
* to an offline CPU?
@ -106,9 +85,9 @@ struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp);
struct rcu_head *rcu_segcblist_first_pend_cb(struct rcu_segcblist *rsclp);
bool rcu_segcblist_nextgp(struct rcu_segcblist *rsclp, unsigned long *lp);
void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy);
struct rcu_head *rhp);
bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp,
struct rcu_head *rhp, bool lazy);
struct rcu_head *rhp);
void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp,
struct rcu_cblist *rclp);
void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp,

4
kernel/rcu/srcutree.c
View File

@ -853,7 +853,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
local_irq_save(flags);
sdp = this_cpu_ptr(ssp->sda);
spin_lock_rcu_node(sdp);
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false);
rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
rcu_segcblist_advance(&sdp->srcu_cblist,
rcu_seq_current(&ssp->srcu_gp_seq));
s = rcu_seq_snap(&ssp->srcu_gp_seq);
@ -1052,7 +1052,7 @@ void srcu_barrier(struct srcu_struct *ssp)
sdp->srcu_barrier_head.func = srcu_barrier_cb;
debug_rcu_head_queue(&sdp->srcu_barrier_head);
if (!rcu_segcblist_entrain(&sdp->srcu_cblist,
&sdp->srcu_barrier_head, 0)) {
&sdp->srcu_barrier_head)) {
debug_rcu_head_unqueue(&sdp->srcu_barrier_head);
atomic_dec(&ssp->srcu_barrier_cpu_cnt);
}

28
kernel/rcu/tiny.c
View File

@ -22,6 +22,7 @@
#include <linux/time.h>
#include <linux/cpu.h>
#include <linux/prefetch.h>
#include <linux/slab.h>
#include "rcu.h"
@ -73,6 +74,31 @@ void rcu_sched_clock_irq(int user)
}
}
/*
* Reclaim the specified callback, either by invoking it for non-kfree cases or
* freeing it directly (for kfree). Return true if kfreeing, false otherwise.
*/
static inline bool rcu_reclaim_tiny(struct rcu_head *head)
{
rcu_callback_t f;
unsigned long offset = (unsigned long)head->func;
rcu_lock_acquire(&rcu_callback_map);
if (__is_kfree_rcu_offset(offset)) {
trace_rcu_invoke_kfree_callback("", head, offset);
kfree((void *)head - offset);
rcu_lock_release(&rcu_callback_map);
return true;
}
trace_rcu_invoke_callback("", head);
f = head->func;
WRITE_ONCE(head->func, (rcu_callback_t)0L);
f(head);
rcu_lock_release(&rcu_callback_map);
return false;
}
/* Invoke the RCU callbacks whose grace period has elapsed. */
static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
{
@ -100,7 +126,7 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused
prefetch(next);
debug_rcu_head_unqueue(list);
local_bh_disable();
__rcu_reclaim("", list);
rcu_reclaim_tiny(list);
local_bh_enable();
list = next;
}

40
kernel/rcu/tree.c
View File

@ -55,6 +55,7 @@
#include <linux/oom.h>
#include <linux/smpboot.h>
#include <linux/jiffies.h>
#include <linux/slab.h>
#include <linux/sched/isolation.h>
#include <linux/sched/clock.h>
#include "../time/tick-internal.h"
@ -2146,7 +2147,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
/* If no callbacks are ready, just return. */
if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), 0);
trace_rcu_batch_end(rcu_state.name, 0,
!rcu_segcblist_empty(&rdp->cblist),
@ -2168,7 +2168,6 @@ static void rcu_do_batch(struct rcu_data *rdp)
if (unlikely(bl > 100))
tlimit = local_clock() + rcu_resched_ns;
trace_rcu_batch_start(rcu_state.name,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist), bl);
rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
if (offloaded)
@ -2179,9 +2178,19 @@ static void rcu_do_batch(struct rcu_data *rdp)
tick_dep_set_task(current, TICK_DEP_BIT_RCU);
rhp = rcu_cblist_dequeue(&rcl);
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
rcu_callback_t f;
debug_rcu_head_unqueue(rhp);
if (__rcu_reclaim(rcu_state.name, rhp))
rcu_cblist_dequeued_lazy(&rcl);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_callback(rcu_state.name, rhp);
f = rhp->func;
WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
f(rhp);
rcu_lock_release(&rcu_callback_map);
/*
* Stop only if limit reached and CPU has something to do.
* Note: The rcl structure counts down from zero.
@ -2583,7 +2592,7 @@ static void rcu_leak_callback(struct rcu_head *rhp)
* is expected to specify a CPU.
*/
static void
__call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
__call_rcu(struct rcu_head *head, rcu_callback_t func)
{
unsigned long flags;
struct rcu_data *rdp;
@ -2618,18 +2627,17 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
if (rcu_segcblist_empty(&rdp->cblist))
rcu_segcblist_init(&rdp->cblist);
}
if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
return; // Enqueued onto ->nocb_bypass, so just leave.
/* If we get here, rcu_nocb_try_bypass() acquired ->nocb_lock. */
rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
rcu_segcblist_enqueue(&rdp->cblist, head);
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rcu_state.name, head,
(unsigned long)func,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
else
trace_rcu_callback(rcu_state.name, head,
rcu_segcblist_n_lazy_cbs(&rdp->cblist),
rcu_segcblist_n_cbs(&rdp->cblist));
/* Go handle any RCU core processing required. */
@ -2679,7 +2687,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
*/
void call_rcu(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, 0);
__call_rcu(head, func);
}
EXPORT_SYMBOL_GPL(call_rcu);
@ -2747,10 +2755,18 @@ static void kfree_rcu_work(struct work_struct *work)
// List "head" is now private, so traverse locklessly.
for (; head; head = next) {
unsigned long offset = (unsigned long)head->func;
next = head->next;
// Potentially optimize with kfree_bulk in future.
debug_rcu_head_unqueue(head);
__rcu_reclaim(rcu_state.name, head);
rcu_lock_acquire(&rcu_callback_map);
trace_rcu_invoke_kfree_callback(rcu_state.name, head, offset);
/* Could be possible to optimize with kfree_bulk in future */
kfree((void *)head - offset);
rcu_lock_release(&rcu_callback_map);
cond_resched_tasks_rcu_qs();
}
}
@ -2825,7 +2841,7 @@ static void kfree_rcu_monitor(struct work_struct *work)
*/
void kfree_call_rcu_nobatch(struct rcu_head *head, rcu_callback_t func)
{
__call_rcu(head, func, 1);
__call_rcu(head, func);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu_nobatch);
@ -3100,7 +3116,7 @@ static void rcu_barrier_func(void *unused)
debug_rcu_head_queue(&rdp->barrier_head);
rcu_nocb_lock(rdp);
WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
atomic_inc(&rcu_state.barrier_cpu_count);
} else {
debug_rcu_head_unqueue(&rdp->barrier_head);

1
kernel/rcu/tree.h
View File

@ -183,7 +183,6 @@ struct rcu_data {
bool rcu_urgent_qs; /* GP old need light quiescent state. */
bool rcu_forced_tick; /* Forced tick to provide QS. */
#ifdef CONFIG_RCU_FAST_NO_HZ
bool all_lazy; /* All CPU's CBs lazy at idle start? */
unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */
unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */
int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */

48
kernel/rcu/tree_plugin.h
View File

@ -1262,10 +1262,9 @@ static void rcu_prepare_for_idle(void)
/*
* This code is invoked when a CPU goes idle, at which point we want
* to have the CPU do everything required for RCU so that it can enter
* the energy-efficient dyntick-idle mode. This is handled by a
* state machine implemented by rcu_prepare_for_idle() below.
* the energy-efficient dyntick-idle mode.
*
* The following three proprocessor symbols control this state machine:
* The following preprocessor symbol controls this:
*
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
* to sleep in dyntick-idle mode with RCU callbacks pending. This
@ -1274,21 +1273,15 @@ static void rcu_prepare_for_idle(void)
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
* system. And if you are -that- concerned about energy efficiency,
* just power the system down and be done with it!
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
* permitted to sleep in dyntick-idle mode with only lazy RCU
* callbacks pending. Setting this too high can OOM your system.
*
* The values below work well in practice. If future workloads require
* The value below works well in practice. If future workloads require
* adjustment, they can be converted into kernel config parameters, though
* making the state machine smarter might be a better option.
*/
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
module_param(rcu_idle_gp_delay, int, 0644);
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
module_param(rcu_idle_lazy_gp_delay, int, 0644);
/*
* Try to advance callbacks on the current CPU, but only if it has been
@ -1327,8 +1320,7 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void)
/*
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
* to invoke. If the CPU has callbacks, try to advance them. Tell the
* caller to set the timeout based on whether or not there are non-lazy
* callbacks.
* caller about what to set the timeout.
*
* The caller must have disabled interrupts.
*/
@ -1354,25 +1346,18 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt)
}
rdp->last_accelerate = jiffies;
/* Request timer delay depending on laziness, and round. */
rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist);
if (rdp->all_lazy) {
dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
} else {
dj = round_up(rcu_idle_gp_delay + jiffies,
rcu_idle_gp_delay) - jiffies;
}
/* Request timer and round. */
dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies;
*nextevt = basemono + dj * TICK_NSEC;
return 0;
}
/*
* Prepare a CPU for idle from an RCU perspective. The first major task
* is to sense whether nohz mode has been enabled or disabled via sysfs.
* The second major task is to check to see if a non-lazy callback has
* arrived at a CPU that previously had only lazy callbacks. The third
* major task is to accelerate (that is, assign grace-period numbers to)
* any recently arrived callbacks.
* Prepare a CPU for idle from an RCU perspective. The first major task is to
* sense whether nohz mode has been enabled or disabled via sysfs. The second
* major task is to accelerate (that is, assign grace-period numbers to) any
* recently arrived callbacks.
*
* The caller must have disabled interrupts.
*/
@ -1398,17 +1383,6 @@ static void rcu_prepare_for_idle(void)
if (!tne)
return;
/*
* If a non-lazy callback arrived at a CPU having only lazy
* callbacks, invoke RCU core for the side-effect of recalculating
* idle duration on re-entry to idle.
*/
if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) {
rdp->all_lazy = false;
invoke_rcu_core();
return;
}
/*
* If we have not yet accelerated this jiffy, accelerate all
* callbacks on this CPU.

6
kernel/rcu/tree_stall.h
View File

@ -263,11 +263,9 @@ static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
sprintf(cp, "last_accelerate: %04lx/%04lx, Nonlazy posted: %c%c%c",
sprintf(cp, "last_accelerate: %04lx/%04lx dyntick_enabled: %d",
rdp->last_accelerate & 0xffff, jiffies & 0xffff,
".l"[rdp->all_lazy],
".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
".D"[!!rdp->tick_nohz_enabled_snap]);
!!rdp->tick_nohz_enabled_snap);
}
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */