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Message-ID: <CACvQF534RJcu8-yKcByqthifUHCLsggGXuRPAKqf7mZMXT3taA@mail.gmail.com>
Date: Sat, 10 Mar 2012 11:16:48 +0800
From: Lai Jiangshan <eag0628@...il.com>
To: paulmck@...ux.vnet.ibm.com
Cc: Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, Valdis.Kletnieks@...edu, dhowells@...hat.com,
eric.dumazet@...il.com, darren@...art.com, fweisbec@...il.com,
patches@...aro.org
Subject: Re: [RFC PATCH 5/5 single-thread-version] implement per-domain
single-thread state machine call_srcu()
On Fri, Mar 9, 2012 at 4:35 AM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> On Wed, Mar 07, 2012 at 11:54:02AM +0800, Lai Jiangshan wrote:
>> This patch is on the top of the 4 previous patches(1/6, 2/6, 3/6, 4/6).
>>
>> o state machine is light way and single-threaded, it is preemptible when checking.
>>
>> o state machine is a work_struct. So, there is no thread occupied
>> by SRCU when the srcu is not actived(no callback). And it does
>> not sleep(avoid to occupy a thread when sleep).
>>
>> o state machine is the only thread can flip/check/write(*) the srcu_struct,
>> so we don't need any mutex.
>> (write(*): except ->per_cpu_ref, ->running, ->batch_queue)
>>
>> o synchronize_srcu() is always call call_srcu().
>> synchronize_srcu_expedited() is also.
>> It is OK for mb()-based srcu are extremely fast.
>>
>> o In current kernel, we can expect that there are only 1 callback per gp.
>> so callback is probably called in the same CPU when it is queued.
>>
>> The trip of a callback:
>> 1) ->batch_queue when call_srcu()
>>
>> 2) ->batch_check0 when try to do check_zero
>>
>> 3) ->batch_check1 after finish its first check_zero and the flip
>>
>> 4) ->batch_done after finish its second check_zero
>>
>> The current requirement of the callbacks:
>> The callback will be called inside process context.
>> The callback should be fast without any sleeping path.
>>
>> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>> ---
>> include/linux/rcupdate.h | 2 +-
>> include/linux/srcu.h | 28 +++++-
>> kernel/rcupdate.c | 24 ++++-
>> kernel/rcutorture.c | 44 ++++++++-
>> kernel/srcu.c | 238 ++++++++++++++++++++++++++++++++-------------
>> 5 files changed, 259 insertions(+), 77 deletions(-)
>> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
>> index 9372174..d98eab2 100644
>> --- a/include/linux/rcupdate.h
>> +++ b/include/linux/rcupdate.h
>> @@ -222,7 +222,7 @@ extern void rcu_irq_exit(void);
>> * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
>> */
>>
>> -typedef void call_rcu_func_t(struct rcu_head *head,
>> +typedef void (*call_rcu_func_t)(struct rcu_head *head,
>
> I don't see what this applies against. The old patch 5/6 created
> a "(*call_rcu_func_t)(struct rcu_head *head," and I don't see what
> created the "call_rcu_func_t(struct rcu_head *head,".
typedef void call_rcu_func_t(...) declares a function type, not a
function pointer
type. I use a line of code as following:
call_rcu_func_t crf = func;
if call_rcu_func_t is a function type, the above code can't be complied,
I need to covert it to function pointer type.
>
>> void (*func)(struct rcu_head *head));
>> void wait_rcu_gp(call_rcu_func_t crf);
>>
>> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
>> index df8f5f7..56cb774 100644
>> --- a/include/linux/srcu.h
>> +++ b/include/linux/srcu.h
>> @@ -29,6 +29,7 @@
>>
>> #include <linux/mutex.h>
>> #include <linux/rcupdate.h>
>> +#include <linux/workqueue.h>
>>
>> struct srcu_struct_array {
>> unsigned long c[2];
>> @@ -39,10 +40,23 @@ struct srcu_struct_array {
>> #define SRCU_REF_MASK (ULONG_MAX >> SRCU_USAGE_BITS)
>> #define SRCU_USAGE_COUNT (SRCU_REF_MASK + 1)
>>
>> +struct rcu_batch {
>> + struct rcu_head *head, **tail;
>> +};
>> +
>> struct srcu_struct {
>> unsigned completed;
>> struct srcu_struct_array __percpu *per_cpu_ref;
>> - struct mutex mutex;
>> + spinlock_t queue_lock; /* protect ->batch_queue, ->running */
>> + bool running;
>> + /* callbacks just queued */
>> + struct rcu_batch batch_queue;
>> + /* callbacks try to do the first check_zero */
>> + struct rcu_batch batch_check0;
>> + /* callbacks done with the first check_zero and the flip */
>> + struct rcu_batch batch_check1;
>> + struct rcu_batch batch_done;
>> + struct delayed_work work;
>
> Why not use your multiple-tail-pointer trick here? (The one that is
> used in treercu.)
1) Make the code of the advance of batches simpler.
2) batch_queue is protected by lock, so it will be hard to use
multiple-tail-pointer trick.
3) rcu_batch API do add a little more runtime overhead, but this
overhead is just
several cpu-instructions, I think it is OK. It is good tradeoff when
compare to the readability.
I think we can also use rcu_batch for rcutree/rcutiny.
>
>> unsigned long snap[NR_CPUS];
>> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>> struct lockdep_map dep_map;
>> @@ -67,12 +81,24 @@ int init_srcu_struct(struct srcu_struct *sp);
>>
>> #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>>
>> +/* draft
>> + * queue callbacks which will be invoked after grace period.
>> + * The callback will be called inside process context.
>> + * The callback should be fast without any sleeping path.
>> + */
>> +void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
>> + void (*func)(struct rcu_head *head));
>> +
>> +typedef void (*call_srcu_func_t)(struct srcu_struct *sp, struct rcu_head *head,
>> + void (*func)(struct rcu_head *head));
>> +void __wait_srcu_gp(struct srcu_struct *sp, call_srcu_func_t crf);
>> void cleanup_srcu_struct(struct srcu_struct *sp);
>> int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
>> void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
>> void synchronize_srcu(struct srcu_struct *sp);
>> void synchronize_srcu_expedited(struct srcu_struct *sp);
>> long srcu_batches_completed(struct srcu_struct *sp);
>> +void srcu_barrier(struct srcu_struct *sp);
>>
>> #ifdef CONFIG_DEBUG_LOCK_ALLOC
>>
>> diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
>> index a86f174..f9b551f 100644
>> --- a/kernel/rcupdate.c
>> +++ b/kernel/rcupdate.c
>> @@ -45,6 +45,7 @@
>> #include <linux/mutex.h>
>> #include <linux/export.h>
>> #include <linux/hardirq.h>
>> +#include <linux/srcu.h>
>>
>> #define CREATE_TRACE_POINTS
>> #include <trace/events/rcu.h>
>> @@ -123,20 +124,39 @@ static void wakeme_after_rcu(struct rcu_head *head)
>> complete(&rcu->completion);
>> }
>>
>> -void wait_rcu_gp(call_rcu_func_t crf)
>> +static void __wait_rcu_gp(void *domain, void *func)
>> {
>> struct rcu_synchronize rcu;
>>
>> init_rcu_head_on_stack(&rcu.head);
>> init_completion(&rcu.completion);
>> +
>> /* Will wake me after RCU finished. */
>> - crf(&rcu.head, wakeme_after_rcu);
>> + if (!domain) {
>> + call_rcu_func_t crf = func;
>> + crf(&rcu.head, wakeme_after_rcu);
>> + } else {
>> + call_srcu_func_t crf = func;
>> + crf(domain, &rcu.head, wakeme_after_rcu);
>> + }
>> +
>> /* Wait for it. */
>> wait_for_completion(&rcu.completion);
>> destroy_rcu_head_on_stack(&rcu.head);
>> }
>
> Mightn't it be simpler and faster to just have a separate wait_srcu_gp()
> that doesn't share code with wait_rcu_gp()? I am all for sharing code,
> but this might be hrting more than helping.
>
>> +
>> +void wait_rcu_gp(call_rcu_func_t crf)
>> +{
>> + __wait_rcu_gp(NULL, crf);
>> +}
>> EXPORT_SYMBOL_GPL(wait_rcu_gp);
>>
>> +/* srcu.c internel */
>> +void __wait_srcu_gp(struct srcu_struct *sp, call_srcu_func_t crf)
>> +{
>> + __wait_rcu_gp(sp, crf);
>> +}
>> +
>> #ifdef CONFIG_PROVE_RCU
>> /*
>> * wrapper function to avoid #include problems.
>> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
>> index 54e5724..40d24d0 100644
>
> OK, so your original patch #6 is folded into this? I don't have a strong
> view either way, just need to know.
>
>> --- a/kernel/rcutorture.c
>> +++ b/kernel/rcutorture.c
>> @@ -623,6 +623,11 @@ static int srcu_torture_completed(void)
>> return srcu_batches_completed(&srcu_ctl);
>> }
>>
>> +static void srcu_torture_deferred_free(struct rcu_torture *rp)
>> +{
>> + call_srcu(&srcu_ctl, &rp->rtort_rcu, rcu_torture_cb);
>> +}
>> +
>> static void srcu_torture_synchronize(void)
>> {
>> synchronize_srcu(&srcu_ctl);
>> @@ -652,7 +657,7 @@ static struct rcu_torture_ops srcu_ops = {
>> .read_delay = srcu_read_delay,
>> .readunlock = srcu_torture_read_unlock,
>> .completed = srcu_torture_completed,
>> - .deferred_free = rcu_sync_torture_deferred_free,
>> + .deferred_free = srcu_torture_deferred_free,
>> .sync = srcu_torture_synchronize,
>> .call = NULL,
>> .cb_barrier = NULL,
>> @@ -660,6 +665,21 @@ static struct rcu_torture_ops srcu_ops = {
>> .name = "srcu"
>> };
>>
>> +static struct rcu_torture_ops srcu_sync_ops = {
>> + .init = srcu_torture_init,
>> + .cleanup = srcu_torture_cleanup,
>> + .readlock = srcu_torture_read_lock,
>> + .read_delay = srcu_read_delay,
>> + .readunlock = srcu_torture_read_unlock,
>> + .completed = srcu_torture_completed,
>> + .deferred_free = rcu_sync_torture_deferred_free,
>> + .sync = srcu_torture_synchronize,
>> + .call = NULL,
>> + .cb_barrier = NULL,
>> + .stats = srcu_torture_stats,
>> + .name = "srcu_sync"
>> +};
>> +
>> static int srcu_torture_read_lock_raw(void) __acquires(&srcu_ctl)
>> {
>> return srcu_read_lock_raw(&srcu_ctl);
>> @@ -677,7 +697,7 @@ static struct rcu_torture_ops srcu_raw_ops = {
>> .read_delay = srcu_read_delay,
>> .readunlock = srcu_torture_read_unlock_raw,
>> .completed = srcu_torture_completed,
>> - .deferred_free = rcu_sync_torture_deferred_free,
>> + .deferred_free = srcu_torture_deferred_free,
>> .sync = srcu_torture_synchronize,
>> .call = NULL,
>> .cb_barrier = NULL,
>> @@ -685,6 +705,21 @@ static struct rcu_torture_ops srcu_raw_ops = {
>> .name = "srcu_raw"
>> };
>>
>> +static struct rcu_torture_ops srcu_raw_sync_ops = {
>> + .init = srcu_torture_init,
>> + .cleanup = srcu_torture_cleanup,
>> + .readlock = srcu_torture_read_lock_raw,
>> + .read_delay = srcu_read_delay,
>> + .readunlock = srcu_torture_read_unlock_raw,
>> + .completed = srcu_torture_completed,
>> + .deferred_free = rcu_sync_torture_deferred_free,
>> + .sync = srcu_torture_synchronize,
>> + .call = NULL,
>> + .cb_barrier = NULL,
>> + .stats = srcu_torture_stats,
>> + .name = "srcu_raw_sync"
>> +};
>> +
>> static void srcu_torture_synchronize_expedited(void)
>> {
>> synchronize_srcu_expedited(&srcu_ctl);
>> @@ -1673,7 +1708,7 @@ static int rcu_torture_barrier_init(void)
>> for (i = 0; i < n_barrier_cbs; i++) {
>> init_waitqueue_head(&barrier_cbs_wq[i]);
>> barrier_cbs_tasks[i] = kthread_run(rcu_torture_barrier_cbs,
>> - (void *)i,
>> + (void *)(long)i,
>> "rcu_torture_barrier_cbs");
>> if (IS_ERR(barrier_cbs_tasks[i])) {
>> ret = PTR_ERR(barrier_cbs_tasks[i]);
>> @@ -1857,7 +1892,8 @@ rcu_torture_init(void)
>> static struct rcu_torture_ops *torture_ops[] =
>> { &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
>> &rcu_bh_ops, &rcu_bh_sync_ops, &rcu_bh_expedited_ops,
>> - &srcu_ops, &srcu_raw_ops, &srcu_expedited_ops,
>> + &srcu_ops, &srcu_sync_ops, &srcu_raw_ops,
>> + &srcu_raw_sync_ops, &srcu_expedited_ops,
>> &sched_ops, &sched_sync_ops, &sched_expedited_ops, };
>>
>> mutex_lock(&fullstop_mutex);
>> diff --git a/kernel/srcu.c b/kernel/srcu.c
>> index d101ed5..532f890 100644
>> --- a/kernel/srcu.c
>> +++ b/kernel/srcu.c
>> @@ -34,10 +34,60 @@
>> #include <linux/delay.h>
>> #include <linux/srcu.h>
>>
>> +static inline void rcu_batch_init(struct rcu_batch *b)
>> +{
>> + b->head = NULL;
>> + b->tail = &b->head;
>> +}
>> +
>> +static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
>> +{
>> + *b->tail = head;
>> + b->tail = &head->next;
>> +}
>> +
>> +static inline bool rcu_batch_empty(struct rcu_batch *b)
>> +{
>> + return b->tail == &b->head;
>> +}
>> +
>> +static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
>> +{
>> + struct rcu_head *head;
>> +
>> + if (rcu_batch_empty(b))
>> + return NULL;
>> +
>> + head = b->head;
>> + b->head = head->next;
>> + if (b->tail == &head->next)
>> + rcu_batch_init(b);
>> +
>> + return head;
>> +}
>> +
>> +static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
>> +{
>> + if (!rcu_batch_empty(from)) {
>> + *to->tail = from->head;
>> + to->tail = from->tail;
>> + rcu_batch_init(from);
>> + }
>> +}
>
> And perhaps this is why you don't want the multi-tailed queue?
>
>> +
>> +/* single-thread state-machine */
>> +static void process_srcu(struct work_struct *work);
>> +
>> static int init_srcu_struct_fields(struct srcu_struct *sp)
>> {
>> sp->completed = 0;
>> - mutex_init(&sp->mutex);
>> + spin_lock_init(&sp->queue_lock);
>> + sp->running = false;
>> + rcu_batch_init(&sp->batch_queue);
>> + rcu_batch_init(&sp->batch_check0);
>> + rcu_batch_init(&sp->batch_check1);
>> + rcu_batch_init(&sp->batch_done);
>> + INIT_DELAYED_WORK(&sp->work, process_srcu);
>> sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
>> return sp->per_cpu_ref ? 0 : -ENOMEM;
>> }
>> @@ -254,11 +304,9 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
>> * we repeatedly block for 1-millisecond time periods. This approach
>> * has done well in testing, so there is no need for a config parameter.
>> */
>> -#define SYNCHRONIZE_SRCU_READER_DELAY 5
>> -#define SYNCHRONIZE_SRCU_TRYCOUNT 2
>> -#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12
>> +#define SRCU_RETRY_CHECK_DELAY 5
>>
>> -static void wait_idx(struct srcu_struct *sp, int idx, int trycount)
>> +static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
>> {
>> /*
>> * If a reader fetches the index before the ->completed increment,
>> @@ -271,19 +319,12 @@ static void wait_idx(struct srcu_struct *sp, int idx, int trycount)
>> */
>> smp_mb(); /* D */
>>
>> - /*
>> - * SRCU read-side critical sections are normally short, so wait
>> - * a small amount of time before possibly blocking.
>> - */
>> - if (!srcu_readers_active_idx_check(sp, idx)) {
>> - udelay(SYNCHRONIZE_SRCU_READER_DELAY);
>> - while (!srcu_readers_active_idx_check(sp, idx)) {
>> - if (trycount > 0) {
>> - trycount--;
>> - udelay(SYNCHRONIZE_SRCU_READER_DELAY);
>> - } else
>> - schedule_timeout_interruptible(1);
>> - }
>> + for (;;) {
>> + if (srcu_readers_active_idx_check(sp, idx))
>> + break;
>> + if (--trycount <= 0)
>> + return false;
>> + udelay(SRCU_RETRY_CHECK_DELAY);
>> }
>>
>> /*
>> @@ -297,6 +338,8 @@ static void wait_idx(struct srcu_struct *sp, int idx, int trycount)
>> * the next flipping.
>> */
>> smp_mb(); /* E */
>> +
>> + return true;
>> }
>>
>> /*
>> @@ -308,10 +351,27 @@ static void srcu_flip(struct srcu_struct *sp)
>> ACCESS_ONCE(sp->completed)++;
>> }
>>
>> +void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
>> + void (*func)(struct rcu_head *head))
>> +{
>> + unsigned long flags;
>> +
>> + head->next = NULL;
>> + head->func = func;
>> + spin_lock_irqsave(&sp->queue_lock, flags);
>> + rcu_batch_queue(&sp->batch_queue, head);
>> + if (!sp->running) {
>> + sp->running = true;
>> + queue_delayed_work(system_nrt_wq, &sp->work, 0);
>> + }
>> + spin_unlock_irqrestore(&sp->queue_lock, flags);
>> +}
>> +EXPORT_SYMBOL_GPL(call_srcu);
>> +
>> /*
>> * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
>> */
>> -static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
>> +static void __synchronize_srcu(struct srcu_struct *sp)
>> {
>> rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
>> !lock_is_held(&rcu_bh_lock_map) &&
>> @@ -319,54 +379,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
>> !lock_is_held(&rcu_sched_lock_map),
>> "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
>>
>> - mutex_lock(&sp->mutex);
>> -
>> - /*
>> - * Suppose that during the previous grace period, a reader
>> - * picked up the old value of the index, but did not increment
>> - * its counter until after the previous instance of
>> - * __synchronize_srcu() did the counter summation and recheck.
>> - * That previous grace period was OK because the reader did
>> - * not start until after the grace period started, so the grace
>> - * period was not obligated to wait for that reader.
>> - *
>> - * However, the current SRCU grace period does have to wait for
>> - * that reader. This is handled by invoking wait_idx() on the
>> - * non-active set of counters (hence sp->completed - 1). Once
>> - * wait_idx() returns, we know that all readers that picked up
>> - * the old value of ->completed and that already incremented their
>> - * counter will have completed.
>> - *
>> - * But what about readers that picked up the old value of
>> - * ->completed, but -still- have not managed to increment their
>> - * counter? We do not need to wait for those readers, because
>> - * they will have started their SRCU read-side critical section
>> - * after the current grace period starts.
>> - *
>> - * Because it is unlikely that readers will be preempted between
>> - * fetching ->completed and incrementing their counter, wait_idx()
>> - * will normally not need to wait.
>> - */
>> - wait_idx(sp, (sp->completed - 1) & 0x1, trycount);
>> -
>> - /*
>> - * Now that wait_idx() has waited for the really old readers,
>> - *
>> - * Flip the readers' index by incrementing ->completed, then wait
>> - * until there are no more readers using the counters referenced by
>> - * the old index value. (Recall that the index is the bottom bit
>> - * of ->completed.)
>> - *
>> - * Of course, it is possible that a reader might be delayed for the
>> - * full duration of flip_idx_and_wait() between fetching the
>> - * index and incrementing its counter. This possibility is handled
>> - * by the next __synchronize_srcu() invoking wait_idx() for such
>> - * readers before starting a new grace period.
>> - */
>> - srcu_flip(sp);
>> - wait_idx(sp, (sp->completed - 1) & 0x1, trycount);
>> -
>> - mutex_unlock(&sp->mutex);
>> + __wait_srcu_gp(sp, call_srcu);
>> }
>>
>> /**
>> @@ -385,7 +398,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
>> */
>> void synchronize_srcu(struct srcu_struct *sp)
>> {
>> - __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);
>> + __synchronize_srcu(sp);
>> }
>> EXPORT_SYMBOL_GPL(synchronize_srcu);
>>
>> @@ -406,10 +419,16 @@ EXPORT_SYMBOL_GPL(synchronize_srcu);
>> */
>> void synchronize_srcu_expedited(struct srcu_struct *sp)
>> {
>> - __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
>> + __synchronize_srcu(sp);
>> }
>
> OK, I'll bite... Why aren't synchronize_srcu_expedited() and
> synchronize_srcu() different?
In mb()-based srcu, synchronize_srcu() is very fast,
synchronize_srcu_expedited() makes less sense than before.
But when wait_srcu_gp() is move back here, I will use
a bigger "trycount" for synchronize_srcu_expedited().
And any problem for srcu_advance_batches()?
Thanks.
Lai
>
> Thanx, Paul
>
>> EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
>>
>> +void srcu_barrier(struct srcu_struct *sp)
>> +{
>> + __synchronize_srcu(sp);
>> +}
>> +EXPORT_SYMBOL_GPL(srcu_barrier);
>> +
>> /**
>> * srcu_batches_completed - return batches completed.
>> * @sp: srcu_struct on which to report batch completion.
>> @@ -423,3 +442,84 @@ long srcu_batches_completed(struct srcu_struct *sp)
>> return sp->completed;
>> }
>> EXPORT_SYMBOL_GPL(srcu_batches_completed);
>> +
>> +#define SRCU_CALLBACK_BATCH 10
>> +#define SRCU_INTERVAL 1
>> +
>> +static void srcu_collect_new(struct srcu_struct *sp)
>> +{
>> + if (!rcu_batch_empty(&sp->batch_queue)) {
>> + spin_lock_irq(&sp->queue_lock);
>> + rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
>> + spin_unlock_irq(&sp->queue_lock);
>> + }
>> +}
>> +
>> +static void srcu_advance_batches(struct srcu_struct *sp)
>> +{
>> + int idx = 1 - (sp->completed & 0x1UL);
>> +
>> + /*
>> + * SRCU read-side critical sections are normally short, so check
>> + * twice after a flip.
>> + */
>> + if (!rcu_batch_empty(&sp->batch_check1) ||
>> + !rcu_batch_empty(&sp->batch_check0)) {
>> + if (try_check_zero(sp, idx, 1)) {
>> + rcu_batch_move(&sp->batch_done, &sp->batch_check1);
>> + rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
>> + if (!rcu_batch_empty(&sp->batch_check1)) {
>> + srcu_flip(sp);
>> + if (try_check_zero(sp, 1 - idx, 2)) {
>> + rcu_batch_move(&sp->batch_done,
>> + &sp->batch_check1);
>> + }
>> + }
>> + }
>> + }
>> +}
>> +
>> +static void srcu_invoke_callbacks(struct srcu_struct *sp)
>> +{
>> + int i;
>> + struct rcu_head *head;
>> +
>> + for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
>> + head = rcu_batch_dequeue(&sp->batch_done);
>> + if (!head)
>> + break;
>> + head->func(head);
>> + }
>> +}
>> +
>> +static void srcu_reschedule(struct srcu_struct *sp)
>> +{
>> + bool running = true;
>> +
>> + if (rcu_batch_empty(&sp->batch_done) &&
>> + rcu_batch_empty(&sp->batch_check1) &&
>> + rcu_batch_empty(&sp->batch_check0) &&
>> + rcu_batch_empty(&sp->batch_queue)) {
>> + spin_lock_irq(&sp->queue_lock);
>> + if (rcu_batch_empty(&sp->batch_queue)) {
>> + sp->running = false;
>> + running = false;
>> + }
>> + spin_unlock_irq(&sp->queue_lock);
>> + }
>> +
>> + if (running)
>> + queue_delayed_work(system_nrt_wq, &sp->work, SRCU_INTERVAL);
>> +}
>> +
>> +static void process_srcu(struct work_struct *work)
>> +{
>> + struct srcu_struct *sp;
>> +
>> + sp = container_of(work, struct srcu_struct, work.work);
>> +
>> + srcu_collect_new(sp);
>> + srcu_advance_batches(sp);
>> + srcu_invoke_callbacks(sp);
>> + srcu_reschedule(sp);
>> +}
>>
>>
>>
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