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rcu: Avoid waking up CPUs having only kfree_rcu() callbacks 

When CONFIG_RCU_FAST_NO_HZ is enabled, RCU will allow a given CPU to
enter dyntick-idle mode even if it still has RCU callbacks queued.
RCU avoids system hangs in this case by scheduling a timer for several
jiffies in the future.  However, if all of the callbacks on that CPU
are from kfree_rcu(), there is no reason to wake the CPU up, as it is
not a problem to defer freeing of memory.

This commit therefore tracks the number of callbacks on a given CPU
that are from kfree_rcu(), and avoids scheduling the timer if all of
a given CPU's callbacks are from kfree_rcu().

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2012-01-06 14:11:30 -08:00 committed by Paul E. McKenney
parent 0bb7b59d6e
commit 486e259340
10 changed files with 153 additions and 47 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/rcupdate.h
View File

@ -841,7 +841,7 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
/* See the kfree_rcu() header comment. */
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
call_rcu(head, (rcu_callback)offset);
kfree_call_rcu(head, (rcu_callback)offset);
}
/**

6
include/linux/rcutiny.h
View File

@ -83,6 +83,12 @@ static inline void synchronize_sched_expedited(void)
synchronize_sched();
}
static inline void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
call_rcu(head, func);
}
#ifdef CONFIG_TINY_RCU
static inline void rcu_preempt_note_context_switch(void)

2
include/linux/rcutree.h
View File

@ -61,6 +61,8 @@ extern void synchronize_rcu_bh(void);
extern void synchronize_sched_expedited(void);
extern void synchronize_rcu_expedited(void);
void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
static inline void synchronize_rcu_bh_expedited(void)
{
synchronize_sched_expedited();

63
include/trace/events/rcu.h
View File

@ -313,19 +313,22 @@ TRACE_EVENT(rcu_prep_idle,
/*
* Tracepoint for the registration of a single RCU callback function.
* The first argument is the type of RCU, the second argument is
* a pointer to the RCU callback itself, and the third element is the
* new RCU callback queue length for the current CPU.
* a pointer to the RCU callback itself, the third element is the
* number of lazy callbacks queued, and the fourth element is the
* total number of callbacks queued.
*/
TRACE_EVENT(rcu_callback,
TP_PROTO(char *rcuname, struct rcu_head *rhp, long qlen),
TP_PROTO(char *rcuname, struct rcu_head *rhp, long qlen_lazy,
long qlen),
TP_ARGS(rcuname, rhp, qlen),
TP_ARGS(rcuname, rhp, qlen_lazy, qlen),
TP_STRUCT__entry(
__field(char *, rcuname)
__field(void *, rhp)
__field(void *, func)
__field(long, qlen_lazy)
__field(long, qlen)
),
@ -333,11 +336,13 @@ TRACE_EVENT(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=%pf %ld",
__entry->rcuname, __entry->rhp, __entry->func, __entry->qlen)
TP_printk("%s rhp=%p func=%pf %ld/%ld",
__entry->rcuname, __entry->rhp, __entry->func,
__entry->qlen_lazy, __entry->qlen)
);
/*
@ -345,20 +350,21 @@ TRACE_EVENT(rcu_callback,
* kfree() form. The first argument is the RCU type, the second argument
* is a pointer to the RCU callback, the third argument is the offset
* of the callback within the enclosing RCU-protected data structure,
* and the fourth argument is the new RCU callback queue length for the
* current CPU.
* the fourth argument is the number of lazy callbacks queued, and the
* fifth argument is the total number of callbacks queued.
*/
TRACE_EVENT(rcu_kfree_callback,
TP_PROTO(char *rcuname, struct rcu_head *rhp, unsigned long offset,
long qlen),
long qlen_lazy, long qlen),
TP_ARGS(rcuname, rhp, offset, qlen),
TP_ARGS(rcuname, rhp, offset, qlen_lazy, qlen),
TP_STRUCT__entry(
__field(char *, rcuname)
__field(void *, rhp)
__field(unsigned long, offset)
__field(long, qlen_lazy)
__field(long, qlen)
),
@ -366,41 +372,45 @@ TRACE_EVENT(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",
TP_printk("%s rhp=%p func=%ld %ld/%ld",
__entry->rcuname, __entry->rhp, __entry->offset,
__entry->qlen)
__entry->qlen_lazy, __entry->qlen)
);
/*
* Tracepoint for marking the beginning rcu_do_batch, performed to start
* RCU callback invocation. The first argument is the RCU flavor,
* the second is the total number of callbacks (including those that
* are not yet ready to be invoked), and the third argument is the
* current RCU-callback batch limit.
* the second is the number of lazy callbacks queued, the third is
* the total number of callbacks queued, and the fourth argument is
* the current RCU-callback batch limit.
*/
TRACE_EVENT(rcu_batch_start,
TP_PROTO(char *rcuname, long qlen, int blimit),
TP_PROTO(char *rcuname, long qlen_lazy, long qlen, int blimit),
TP_ARGS(rcuname, qlen, blimit),
TP_ARGS(rcuname, qlen_lazy, qlen, blimit),
TP_STRUCT__entry(
__field(char *, rcuname)
__field(long, qlen_lazy)
__field(long, qlen)
__field(int, blimit)
),
TP_fast_assign(
__entry->rcuname = rcuname;
__entry->qlen_lazy = qlen_lazy;
__entry->qlen = qlen;
__entry->blimit = blimit;
),
TP_printk("%s CBs=%ld bl=%d",
__entry->rcuname, __entry->qlen, __entry->blimit)
TP_printk("%s CBs=%ld/%ld bl=%d",
__entry->rcuname, __entry->qlen_lazy, __entry->qlen,
__entry->blimit)
);
/*
@ -531,16 +541,21 @@ TRACE_EVENT(rcu_torture_read,
#else /* #ifdef CONFIG_RCU_TRACE */
#define trace_rcu_grace_period(rcuname, gpnum, gpevent) do { } while (0)
#define trace_rcu_grace_period_init(rcuname, gpnum, level, grplo, grphi, qsmask) do { } while (0)
#define trace_rcu_grace_period_init(rcuname, gpnum, level, grplo, grphi, \
qsmask) do { } while (0)
#define trace_rcu_preempt_task(rcuname, pid, gpnum) do { } while (0)
#define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0)
#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0)
#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, \
grplo, grphi, gp_tasks) do { } \
while (0)
#define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0)
#define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0)
#define trace_rcu_prep_idle(reason) do { } while (0)
#define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0)
#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0)
#define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)
#define trace_rcu_callback(rcuname, rhp, qlen_lazy, qlen) do { } while (0)
#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen_lazy, qlen) \
do { } while (0)
#define trace_rcu_batch_start(rcuname, qlen_lazy, qlen, blimit) \
do { } while (0)
#define trace_rcu_invoke_callback(rcuname, rhp) do { } while (0)
#define trace_rcu_invoke_kfree_callback(rcuname, rhp, offset) do { } while (0)
#define trace_rcu_batch_end(rcuname, callbacks_invoked, cb, nr, iit, risk) \

4
kernel/rcu.h
View File

@ -76,16 +76,18 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head)
extern void kfree(const void *);
static inline void __rcu_reclaim(char *rn, struct rcu_head *head)
static inline bool __rcu_reclaim(char *rn, struct rcu_head *head)
{
unsigned long offset = (unsigned long)head->func;
if (__is_kfree_rcu_offset(offset)) {
RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
kfree((void *)head - offset);
return 1;
} else {
RCU_TRACE(trace_rcu_invoke_callback(rn, head));
head->func(head);
return 0;
}
}

4
kernel/rcutiny.c
View File

@ -258,7 +258,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail) {
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
ACCESS_ONCE(rcp->rcucblist),
need_resched(),
@ -269,7 +269,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;

29
kernel/rcutree.c
View File

@ -1261,6 +1261,7 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp)
*receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
receive_rdp->qlen_lazy += rdp->qlen_lazy;
receive_rdp->qlen += rdp->qlen;
receive_rdp->n_cbs_adopted += rdp->qlen;
rdp->n_cbs_orphaned += rdp->qlen;
@ -1268,6 +1269,7 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp)
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
}
@ -1368,11 +1370,11 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
int bl, count;
int bl, count, count_lazy;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
trace_rcu_batch_start(rsp->name, 0, 0);
trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
need_resched(), is_idle_task(current),
rcu_is_callbacks_kthread());
@ -1385,7 +1387,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
*/
local_irq_save(flags);
bl = rdp->blimit;
trace_rcu_batch_start(rsp->name, rdp->qlen, bl);
trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@ -1396,12 +1398,13 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
local_irq_restore(flags);
/* Invoke callbacks. */
count = 0;
count = count_lazy = 0;
while (list) {
next = list->next;
prefetch(next);
debug_rcu_head_unqueue(list);
__rcu_reclaim(rsp->name, list);
if (__rcu_reclaim(rsp->name, list))
count_lazy++;
list = next;
/* Stop only if limit reached and CPU has something to do. */
if (++count >= bl &&
@ -1416,6 +1419,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
rcu_is_callbacks_kthread());
/* Update count, and requeue any remaining callbacks. */
rdp->qlen_lazy -= count_lazy;
rdp->qlen -= count;
rdp->n_cbs_invoked += count;
if (list != NULL) {
@ -1702,7 +1706,7 @@ static void invoke_rcu_core(void)
static void
__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
struct rcu_state *rsp)
struct rcu_state *rsp, bool lazy)
{
unsigned long flags;
struct rcu_data *rdp;
@ -1727,12 +1731,14 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
*rdp->nxttail[RCU_NEXT_TAIL] = head;
rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
rdp->qlen++;
if (lazy)
rdp->qlen_lazy++;
if (__is_kfree_rcu_offset((unsigned long)func))
trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
rdp->qlen);
rdp->qlen_lazy, rdp->qlen);
else
trace_rcu_callback(rsp->name, head, rdp->qlen);
trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
/* If interrupts were disabled, don't dive into RCU core. */
if (irqs_disabled_flags(flags)) {
@ -1779,16 +1785,16 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
*/
void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_sched_state);
__call_rcu(head, func, &rcu_sched_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_sched);
/*
* Queue an RCU for invocation after a quicker grace period.
* Queue an RCU callback for invocation after a quicker grace period.
*/
void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_bh_state);
__call_rcu(head, func, &rcu_bh_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu_bh);
@ -2036,6 +2042,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->nxtlist = NULL;
for (i = 0; i < RCU_NEXT_SIZE; i++)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen_lazy = 0;
rdp->qlen = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);

3
kernel/rcutree.h
View File

@ -265,7 +265,8 @@ struct rcu_data {
*/
struct rcu_head *nxtlist;
struct rcu_head **nxttail[RCU_NEXT_SIZE];
long qlen; /* # of queued callbacks */
long qlen_lazy; /* # of lazy queued callbacks */
long qlen; /* # of queued callbacks, incl lazy */
long qlen_last_fqs_check;
/* qlen at last check for QS forcing */
unsigned long n_cbs_invoked; /* count of RCU cbs invoked. */

75
kernel/rcutree_plugin.h
View File

@ -671,10 +671,24 @@ static void rcu_preempt_do_callbacks(void)
*/
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state);
__call_rcu(head, func, &rcu_preempt_state, 0);
}
EXPORT_SYMBOL_GPL(call_rcu);
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_preempt_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/**
* synchronize_rcu - wait until a grace period has elapsed.
*
@ -1064,6 +1078,22 @@ static void rcu_preempt_process_callbacks(void)
{
}
/*
* Queue an RCU callback for lazy invocation after a grace period.
* This will likely be later named something like "call_rcu_lazy()",
* but this change will require some way of tagging the lazy RCU
* callbacks in the list of pending callbacks. Until then, this
* function may only be called from __kfree_rcu().
*
* Because there is no preemptible RCU, we use RCU-sched instead.
*/
void kfree_call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
__call_rcu(head, func, &rcu_sched_state, 1);
}
EXPORT_SYMBOL_GPL(kfree_call_rcu);
/*
* Wait for an rcu-preempt grace period, but make it happen quickly.
* But because preemptible RCU does not exist, map to rcu-sched.
@ -2051,6 +2081,48 @@ int rcu_needs_cpu(int cpu)
return per_cpu(rcu_dyntick_holdoff, cpu) == jiffies;
}
/*
* Does the specified flavor of RCU have non-lazy callbacks pending on
* the specified CPU? Both RCU flavor and CPU are specified by the
* rcu_data structure.
*/
static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
{
return rdp->qlen != rdp->qlen_lazy;
}
#ifdef CONFIG_TREE_PREEMPT_RCU
/*
* Are there non-lazy RCU-preempt callbacks? (There cannot be if there
* is no RCU-preempt in the kernel.)
*/
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
return __rcu_cpu_has_nonlazy_callbacks(rdp);
}
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
{
return 0;
}
#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
/*
* Does any flavor of RCU have non-lazy callbacks on the specified CPU?
*/
static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
{
return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
__rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
}
/*
* Timer handler used to force CPU to start pushing its remaining RCU
* callbacks in the case where it entered dyntick-idle mode with callbacks
@ -2149,6 +2221,7 @@ static void rcu_prepare_for_idle(int cpu)
trace_rcu_prep_idle("Dyntick with callbacks");
per_cpu(rcu_dyntick_drain, cpu) = 0;
per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
if (rcu_cpu_has_nonlazy_callbacks(cpu))
hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),
rcu_idle_gp_wait, HRTIMER_MODE_REL);
return; /* Nothing more to do immediately. */

8
kernel/rcutree_trace.c
View File

@ -73,8 +73,8 @@ static void print_one_rcu_data(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, " of=%lu ri=%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, " ql=%ld qs=%c%c%c%c",
rdp->qlen,
seq_printf(m, " ql=%ld/%ld qs=%c%c%c%c",
rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@ -145,7 +145,7 @@ static void print_one_rcu_data_csv(struct seq_file *m, struct rcu_data *rdp)
rdp->dynticks->dynticks_nmi_nesting,
rdp->dynticks_fqs);
seq_printf(m, ",%lu,%lu", rdp->offline_fqs, rdp->resched_ipi);
seq_printf(m, ",%ld,\"%c%c%c%c\"", rdp->qlen,
seq_printf(m, ",%ld,%ld,\"%c%c%c%c\"", rdp->qlen_lazy, rdp->qlen,
".N"[rdp->nxttail[RCU_NEXT_READY_TAIL] !=
rdp->nxttail[RCU_NEXT_TAIL]],
".R"[rdp->nxttail[RCU_WAIT_TAIL] !=
@ -168,7 +168,7 @@ static int show_rcudata_csv(struct seq_file *m, void *unused)
{
seq_puts(m, "\"CPU\",\"Online?\",\"c\",\"g\",\"pq\",\"pgp\",\"pq\",");
seq_puts(m, "\"dt\",\"dt nesting\",\"dt NMI nesting\",\"df\",");
seq_puts(m, "\"of\",\"ri\",\"ql\",\"qs\"");
seq_puts(m, "\"of\",\"ri\",\"qll\",\"ql\",\"qs\"");
#ifdef CONFIG_RCU_BOOST
seq_puts(m, "\"kt\",\"ktl\"");
#endif /* #ifdef CONFIG_RCU_BOOST */