From: Dipankar Sarma Avoids per_cpu calculations and also prepares for call_rcu_bh(). 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 Signed-off-by: Andrew Morton --- 25-akpm/include/linux/rcupdate.h | 38 +++--- 25-akpm/kernel/rcupdate.c | 229 ++++++++++++++++++++------------------- 25-akpm/kernel/sched.c | 2 3 files changed, 143 insertions(+), 126 deletions(-) diff -puN include/linux/rcupdate.h~rcu-clean-up-code include/linux/rcupdate.h --- 25/include/linux/rcupdate.h~rcu-clean-up-code Fri Aug 6 15:13:55 2004 +++ 25-akpm/include/linux/rcupdate.h Fri Aug 6 15:13:55 2004 @@ -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-clean-up-code kernel/rcupdate.c --- 25/kernel/rcupdate.c~rcu-clean-up-code Fri Aug 6 15:13:55 2004 +++ 25-akpm/kernel/rcupdate.c Fri Aug 6 15:13:55 2004 @@ -17,9 +17,10 @@ * * Copyright (C) IBM Corporation, 2001 * - * Author: Dipankar Sarma + * Authors: Dipankar Sarma + * Manfred Spraul * - * Based on the original work by Paul McKenney + * Based on the original work by Paul McKenney * 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-clean-up-code kernel/sched.c --- 25/kernel/sched.c~rcu-clean-up-code Fri Aug 6 15:13:55 2004 +++ 25-akpm/kernel/sched.c Fri Aug 6 15:13:55 2004 @@ -2703,7 +2703,7 @@ 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) { _