Avoids per_cpu calculations and also prepares for call_rcu_bh().
Thanks
Dipankar
At OLS, Rusty had suggested getting rid of many per_cpu() calculations
in RCU code and making the code simpler. I had already done that for
the rcu-softirq patch earlier, so I am splitting that into two
patch. This first patch cleans up the macros and uses pointers
to the rcu per-cpu data directly to manipulate the callback
queues. This is useful for the call-rcu-bh patch (to follow) which introduces
a new RCU mechanism - call_rcu_bh(). Both generic and softirq rcu
can then use the same code, they work different global and
percpu data.
Signed-off-by: Dipankar Sarma <dipankar@xxxxxxxxxx>
include/linux/rcupdate.h | 38 ++++---
kernel/rcupdate.c | 229 ++++++++++++++++++++++++-----------------------
kernel/sched.c | 2
3 files changed, 143 insertions(+), 126 deletions(-)
diff -puN include/linux/rcupdate.h~rcu-code-cleanup include/linux/rcupdate.h
--- linux-2.6.8-rc3-mm1/include/linux/rcupdate.h~rcu-code-cleanup
2004-08-07 15:28:30.000000000 +0530
+++ linux-2.6.8-rc3-mm1-dipankar/include/linux/rcupdate.h 2004-08-07
15:28:30.000000000 +0530
@@ -101,47 +101,51 @@ struct rcu_data {
struct rcu_head **curtail;
struct rcu_head *donelist;
struct rcu_head **donetail;
+ int cpu;
};
DECLARE_PER_CPU(struct rcu_data, rcu_data);
extern struct rcu_ctrlblk rcu_ctrlblk;
-#define RCU_quiescbatch(cpu) (per_cpu(rcu_data, (cpu)).quiescbatch)
-#define RCU_qsctr(cpu) (per_cpu(rcu_data, (cpu)).qsctr)
-#define RCU_last_qsctr(cpu) (per_cpu(rcu_data, (cpu)).last_qsctr)
-#define RCU_qs_pending(cpu) (per_cpu(rcu_data, (cpu)).qs_pending)
-#define RCU_batch(cpu) (per_cpu(rcu_data, (cpu)).batch)
-#define RCU_nxtlist(cpu) (per_cpu(rcu_data, (cpu)).nxtlist)
-#define RCU_curlist(cpu) (per_cpu(rcu_data, (cpu)).curlist)
-#define RCU_nxttail(cpu) (per_cpu(rcu_data, (cpu)).nxttail)
-#define RCU_curtail(cpu) (per_cpu(rcu_data, (cpu)).curtail)
-#define RCU_donelist(cpu) (per_cpu(rcu_data, (cpu)).donelist)
-#define RCU_donetail(cpu) (per_cpu(rcu_data, (cpu)).donetail)
+/*
+ * Increment the quiscent state counter.
+ */
+static inline void rcu_qsctr_inc(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ rdp->qsctr++;
+}
-static inline int rcu_pending(int cpu)
+static inline int __rcu_pending(struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
{
/* This cpu has pending rcu entries and the grace period
* for them has completed.
*/
- if (RCU_curlist(cpu) &&
- !rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu)))
+ if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
return 1;
/* This cpu has no pending entries, but there are new entries */
- if (!RCU_curlist(cpu) && RCU_nxtlist(cpu))
+ if (!rdp->curlist && rdp->nxtlist)
return 1;
- if (RCU_donelist(cpu))
+ /* This cpu has finished callbacks to invoke */
+ if (rdp->donelist)
return 1;
/* The rcu core waits for a quiescent state from the cpu */
- if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur || RCU_qs_pending(cpu))
+ if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
return 1;
/* nothing to do */
return 0;
}
+static inline int rcu_pending(int cpu)
+{
+ return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu));
+}
+
#define rcu_read_lock() preempt_disable()
#define rcu_read_unlock() preempt_enable()
diff -puN kernel/rcupdate.c~rcu-code-cleanup kernel/rcupdate.c
--- linux-2.6.8-rc3-mm1/kernel/rcupdate.c~rcu-code-cleanup 2004-08-07
15:28:30.000000000 +0530
+++ linux-2.6.8-rc3-mm1-dipankar/kernel/rcupdate.c 2004-08-07
15:28:30.000000000 +0530
@@ -17,9 +17,10 @@
*
* Copyright (C) IBM Corporation, 2001
*
- * Author: Dipankar Sarma <dipankar@xxxxxxxxxx>
+ * Authors: Dipankar Sarma <dipankar@xxxxxxxxxx>
+ * Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
*
- * Based on the original work by Paul McKenney <paul.mckenney@xxxxxxxxxx>
+ * Based on the original work by Paul McKenney <paulmck@xxxxxxxxxx>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
@@ -51,19 +52,20 @@ struct rcu_ctrlblk rcu_ctrlblk =
{ .cur = -300, .completed = -300 , .lock = SEQCNT_ZERO };
/* Bookkeeping of the progress of the grace period */
-struct {
- spinlock_t mutex; /* Guard this struct and writes to rcu_ctrlblk */
- cpumask_t rcu_cpu_mask; /* CPUs that need to switch in order */
+struct rcu_state {
+ spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */
+ cpumask_t cpumask; /* CPUs that need to switch in order */
/* for current batch to proceed. */
-} rcu_state ____cacheline_maxaligned_in_smp =
- {.mutex = SPIN_LOCK_UNLOCKED, .rcu_cpu_mask = CPU_MASK_NONE };
+};
+
+struct rcu_state rcu_state ____cacheline_maxaligned_in_smp =
+ {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE };
DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
/* Fake initialization required by compiler */
static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
-#define RCU_tasklet(cpu) (per_cpu(rcu_tasklet, cpu))
static int maxbatch = 10;
/**
@@ -79,15 +81,15 @@ static int maxbatch = 10;
void fastcall call_rcu(struct rcu_head *head,
void (*func)(struct rcu_head *rcu))
{
- int cpu;
unsigned long flags;
+ struct rcu_data *rdp;
head->func = func;
head->next = NULL;
local_irq_save(flags);
- cpu = smp_processor_id();
- *RCU_nxttail(cpu) = head;
- RCU_nxttail(cpu) = &head->next;
+ rdp = &__get_cpu_var(rcu_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
local_irq_restore(flags);
}
@@ -95,23 +97,23 @@ void fastcall call_rcu(struct rcu_head *
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
*/
-static void rcu_do_batch(int cpu)
+static void rcu_do_batch(struct rcu_data *rdp)
{
struct rcu_head *next, *list;
int count = 0;
- list = RCU_donelist(cpu);
+ list = rdp->donelist;
while (list) {
- next = RCU_donelist(cpu) = list->next;
+ next = rdp->donelist = list->next;
list->func(list);
list = next;
if (++count >= maxbatch)
break;
}
- if (!RCU_donelist(cpu))
- RCU_donetail(cpu) = &RCU_donelist(cpu);
+ if (!rdp->donelist)
+ rdp->donetail = &rdp->donelist;
else
- tasklet_schedule(&RCU_tasklet(cpu));
+ tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
}
/*
@@ -119,15 +121,15 @@ static void rcu_do_batch(int cpu)
* The grace period handling consists out of two steps:
* - A new grace period is started.
* This is done by rcu_start_batch. The start is not broadcasted to
- * all cpus, they must pick this up by comparing rcu_ctrlblk.cur with
- * RCU_quiescbatch(cpu). All cpus are recorded in the
- * rcu_state.rcu_cpu_mask bitmap.
+ * all cpus, they must pick this up by comparing rcp->cur with
+ * rdp->quiescbatch. All cpus are recorded in the
+ * rcu_state.cpumask bitmap.
* - All cpus must go through a quiescent state.
* Since the start of the grace period is not broadcasted, at least two
* calls to rcu_check_quiescent_state are required:
* The first call just notices that a new grace period is running. The
* following calls check if there was a quiescent state since the beginning
- * of the grace period. If so, it updates rcu_state.rcu_cpu_mask. If
+ * of the grace period. If so, it updates rcu_state.cpumask. If
* the bitmap is empty, then the grace period is completed.
* rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
* period (if necessary).
@@ -135,22 +137,22 @@ static void rcu_do_batch(int cpu)
/*
* Register a new batch of callbacks, and start it up if there is currently no
* active batch and the batch to be registered has not already occurred.
- * Caller must hold rcu_state.mutex.
+ * Caller must hold rcu_state.lock.
*/
-static void rcu_start_batch(int next_pending)
+static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp,
+ int next_pending)
{
if (next_pending)
- rcu_ctrlblk.next_pending = 1;
+ rcp->next_pending = 1;
- if (rcu_ctrlblk.next_pending &&
- rcu_ctrlblk.completed == rcu_ctrlblk.cur) {
+ if (rcp->next_pending &&
+ rcp->completed == rcp->cur) {
/* Can't change, since spin lock held. */
- cpus_andnot(rcu_state.rcu_cpu_mask, cpu_online_map,
- nohz_cpu_mask);
- write_seqcount_begin(&rcu_ctrlblk.lock);
- rcu_ctrlblk.next_pending = 0;
- rcu_ctrlblk.cur++;
- write_seqcount_end(&rcu_ctrlblk.lock);
+ cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
+ write_seqcount_begin(&rcp->lock);
+ rcp->next_pending = 0;
+ rcp->cur++;
+ write_seqcount_end(&rcp->lock);
}
}
@@ -159,13 +161,13 @@ static void rcu_start_batch(int next_pen
* Clear it from the cpu mask and complete the grace period if it was the last
* cpu. Start another grace period if someone has further entries pending
*/
-static void cpu_quiet(int cpu)
+static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp)
{
- cpu_clear(cpu, rcu_state.rcu_cpu_mask);
- if (cpus_empty(rcu_state.rcu_cpu_mask)) {
+ cpu_clear(cpu, rsp->cpumask);
+ if (cpus_empty(rsp->cpumask)) {
/* batch completed ! */
- rcu_ctrlblk.completed = rcu_ctrlblk.cur;
- rcu_start_batch(0);
+ rcp->completed = rcp->cur;
+ rcu_start_batch(rcp, rsp, 0);
}
}
@@ -174,15 +176,14 @@ static void cpu_quiet(int cpu)
* switch). If so and if it already hasn't done so in this RCU
* quiescent cycle, then indicate that it has done so.
*/
-static void rcu_check_quiescent_state(void)
+static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
+ struct rcu_state *rsp, struct rcu_data *rdp)
{
- int cpu = smp_processor_id();
-
- if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur) {
+ if (rdp->quiescbatch != rcp->cur) {
/* new grace period: record qsctr value. */
- RCU_qs_pending(cpu) = 1;
- RCU_last_qsctr(cpu) = RCU_qsctr(cpu);
- RCU_quiescbatch(cpu) = rcu_ctrlblk.cur;
+ rdp->qs_pending = 1;
+ rdp->last_qsctr = rdp->qsctr;
+ rdp->quiescbatch = rcp->cur;
return;
}
@@ -190,7 +191,7 @@ static void rcu_check_quiescent_state(vo
* qs_pending is checked instead of the actual bitmap to avoid
* cacheline trashing.
*/
- if (!RCU_qs_pending(cpu))
+ if (!rdp->qs_pending)
return;
/*
@@ -198,19 +199,19 @@ static void rcu_check_quiescent_state(vo
* we may miss one quiescent state of that CPU. That is
* tolerable. So no need to disable interrupts.
*/
- if (RCU_qsctr(cpu) == RCU_last_qsctr(cpu))
+ if (rdp->qsctr == rdp->last_qsctr)
return;
- RCU_qs_pending(cpu) = 0;
+ rdp->qs_pending = 0;
- spin_lock(&rcu_state.mutex);
+ spin_lock(&rsp->lock);
/*
- * RCU_quiescbatch/batch.cur and the cpu bitmap can come out of sync
+ * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
* during cpu startup. Ignore the quiescent state.
*/
- if (likely(RCU_quiescbatch(cpu) == rcu_ctrlblk.cur))
- cpu_quiet(cpu);
+ if (likely(rdp->quiescbatch == rcp->cur))
+ cpu_quiet(rdp->cpu, rcp, rsp);
- spin_unlock(&rcu_state.mutex);
+ spin_unlock(&rsp->lock);
}
@@ -220,33 +221,39 @@ static void rcu_check_quiescent_state(vo
* locking requirements, the list it's pulling from has to belong to a cpu
* which is dead and hence not processing interrupts.
*/
-static void rcu_move_batch(struct rcu_head *list, struct rcu_head **tail)
+static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
+ struct rcu_head **tail)
{
- int cpu;
-
local_irq_disable();
- cpu = smp_processor_id();
- *RCU_nxttail(cpu) = list;
+ *this_rdp->nxttail = list;
if (list)
- RCU_nxttail(cpu) = tail;
+ this_rdp->nxttail = tail;
local_irq_enable();
}
-static void rcu_offline_cpu(int cpu)
+static void __rcu_offline_cpu(struct rcu_data *this_rdp,
+ struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp)
{
/* if the cpu going offline owns the grace period
* we can block indefinitely waiting for it, so flush
* it here
*/
- spin_lock_bh(&rcu_state.mutex);
- if (rcu_ctrlblk.cur != rcu_ctrlblk.completed)
- cpu_quiet(cpu);
- spin_unlock_bh(&rcu_state.mutex);
+ spin_lock_bh(&rsp->lock);
+ if (rcp->cur != rcp->completed)
+ cpu_quiet(rdp->cpu, rcp, rsp);
+ spin_unlock_bh(&rsp->lock);
+ rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
+ rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
- rcu_move_batch(RCU_curlist(cpu), RCU_curtail(cpu));
- rcu_move_batch(RCU_nxtlist(cpu), RCU_nxttail(cpu));
+}
+static void rcu_offline_cpu(int cpu)
+{
+ struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
- tasklet_kill_immediate(&RCU_tasklet(cpu), cpu);
+ __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state,
+ &per_cpu(rcu_data, cpu));
+ put_cpu_var(rcu_data);
+ tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
}
#else
@@ -257,81 +264,87 @@ static void rcu_offline_cpu(int cpu)
#endif
-void rcu_restart_cpu(int cpu)
-{
- spin_lock_bh(&rcu_state.mutex);
- RCU_quiescbatch(cpu) = rcu_ctrlblk.completed;
- RCU_qs_pending(cpu) = 0;
- spin_unlock_bh(&rcu_state.mutex);
-}
-
/*
* This does the RCU processing work from tasklet context.
*/
-static void rcu_process_callbacks(unsigned long unused)
+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
+ struct rcu_state *rsp, struct rcu_data *rdp)
{
- int cpu = smp_processor_id();
-
- if (RCU_curlist(cpu) &&
- !rcu_batch_before(rcu_ctrlblk.completed, RCU_batch(cpu))) {
- *RCU_donetail(cpu) = RCU_curlist(cpu);
- RCU_donetail(cpu) = RCU_curtail(cpu);
- RCU_curlist(cpu) = NULL;
- RCU_curtail(cpu) = &RCU_curlist(cpu);
+ if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
+ *rdp->donetail = rdp->curlist;
+ rdp->donetail = rdp->curtail;
+ rdp->curlist = NULL;
+ rdp->curtail = &rdp->curlist;
}
local_irq_disable();
- if (RCU_nxtlist(cpu) && !RCU_curlist(cpu)) {
+ if (rdp->nxtlist && !rdp->curlist) {
int next_pending, seq;
- RCU_curlist(cpu) = RCU_nxtlist(cpu);
- RCU_curtail(cpu) = RCU_nxttail(cpu);
- RCU_nxtlist(cpu) = NULL;
- RCU_nxttail(cpu) = &RCU_nxtlist(cpu);
+ rdp->curlist = rdp->nxtlist;
+ rdp->curtail = rdp->nxttail;
+ rdp->nxtlist = NULL;
+ rdp->nxttail = &rdp->nxtlist;
local_irq_enable();
/*
* start the next batch of callbacks
*/
do {
- seq = read_seqcount_begin(&rcu_ctrlblk.lock);
+ seq = read_seqcount_begin(&rcp->lock);
/* determine batch number */
- RCU_batch(cpu) = rcu_ctrlblk.cur + 1;
- next_pending = rcu_ctrlblk.next_pending;
- } while (read_seqcount_retry(&rcu_ctrlblk.lock, seq));
+ rdp->batch = rcp->cur + 1;
+ next_pending = rcp->next_pending;
+ } while (read_seqcount_retry(&rcp->lock, seq));
if (!next_pending) {
/* and start it/schedule start if it's a new batch */
- spin_lock(&rcu_state.mutex);
- rcu_start_batch(1);
- spin_unlock(&rcu_state.mutex);
+ spin_lock(&rsp->lock);
+ rcu_start_batch(rcp, rsp, 1);
+ spin_unlock(&rsp->lock);
}
} else {
local_irq_enable();
}
- rcu_check_quiescent_state();
- if (RCU_donelist(cpu))
- rcu_do_batch(cpu);
+ rcu_check_quiescent_state(rcp, rsp, rdp);
+ if (rdp->donelist)
+ rcu_do_batch(rdp);
+}
+
+static void rcu_process_callbacks(unsigned long unused)
+{
+ __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state,
+ &__get_cpu_var(rcu_data));
}
void rcu_check_callbacks(int cpu, int user)
{
+ struct rcu_data *rdp = &__get_cpu_var(rcu_data);
if (user ||
(idle_cpu(cpu) && !in_softirq() &&
hardirq_count() <= (1 << HARDIRQ_SHIFT)))
- RCU_qsctr(cpu)++;
- tasklet_schedule(&RCU_tasklet(cpu));
+ rdp->qsctr++;
+ tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
+}
+
+static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ memset(rdp, 0, sizeof(*rdp));
+ rdp->curtail = &rdp->curlist;
+ rdp->nxttail = &rdp->nxtlist;
+ rdp->donetail = &rdp->donelist;
+ rdp->quiescbatch = rcp->completed;
+ rdp->qs_pending = 0;
+ rdp->cpu = cpu;
}
static void __devinit rcu_online_cpu(int cpu)
{
- memset(&per_cpu(rcu_data, cpu), 0, sizeof(struct rcu_data));
- tasklet_init(&RCU_tasklet(cpu), rcu_process_callbacks, 0UL);
- RCU_curtail(cpu) = &RCU_curlist(cpu);
- RCU_nxttail(cpu) = &RCU_nxtlist(cpu);
- RCU_donetail(cpu) = &RCU_donelist(cpu);
- RCU_quiescbatch(cpu) = rcu_ctrlblk.completed;
- RCU_qs_pending(cpu) = 0;
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+
+ rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
+ tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
}
static int __devinit rcu_cpu_notify(struct notifier_block *self,
diff -puN kernel/sched.c~rcu-code-cleanup kernel/sched.c
--- linux-2.6.8-rc3-mm1/kernel/sched.c~rcu-code-cleanup 2004-08-07
15:28:30.000000000 +0530
+++ linux-2.6.8-rc3-mm1-dipankar/kernel/sched.c 2004-08-07 15:28:30.000000000
+0530
@@ -2548,7 +2548,7 @@ need_resched:
switch_tasks:
prefetch(next);
clear_tsk_need_resched(prev);
- RCU_qsctr(task_cpu(prev))++;
+ rcu_qsctr_inc(task_cpu(prev));
prev->sleep_avg -= run_time;
if ((long)prev->sleep_avg <= 0) {
_
|