Re: [PATCH 1/5] Add call_rcu_sched()
From: Gautham R Shenoy
Date: Mon May 05 2008 - 05:16:30 EST
On Mon, Apr 21, 2008 at 05:50:31PM -0700, Paul E. McKenney wrote:
>
Yet to review the complete series.
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> ---
>
> include/linux/rcuclassic.h | 3
> include/linux/rcupdate.h | 22 +
> include/linux/rcupreempt.h | 42 +++
> include/linux/rcupreempt_trace.h | 6
> init/main.c | 1
> kernel/rcupdate.c | 20 -
> kernel/rcupreempt.c | 433 +++++++++++++++++++++++++++++++++++----
> kernel/rcupreempt_trace.c | 58 +++++
> 8 files changed, 514 insertions(+), 71 deletions(-)
>
> diff -urpNa -X dontdiff linux-2.6.25/include/linux/rcuclassic.h linux-2.6.25-C1-call_rcu_sched/include/linux/rcuclassic.h
> --- linux-2.6.25/include/linux/rcuclassic.h 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/include/linux/rcuclassic.h 2008-04-17 08:10:33.000000000 -0700
> @@ -153,7 +153,10 @@ extern struct lockdep_map rcu_lock_map;
>
> #define __synchronize_sched() synchronize_rcu()
>
> +#define call_rcu_sched(head, func) call_rcu(head, func)
> +
> extern void __rcu_init(void);
> +#define rcu_init_sched() do { } while (0)
> extern void rcu_check_callbacks(int cpu, int user);
> extern void rcu_restart_cpu(int cpu);
>
> diff -urpNa -X dontdiff linux-2.6.25/include/linux/rcupdate.h linux-2.6.25-C1-call_rcu_sched/include/linux/rcupdate.h
> --- linux-2.6.25/include/linux/rcupdate.h 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/include/linux/rcupdate.h 2008-04-17 08:10:33.000000000 -0700
> @@ -42,6 +42,7 @@
> #include <linux/cpumask.h>
> #include <linux/seqlock.h>
> #include <linux/lockdep.h>
> +#include <linux/completion.h>
>
> /**
> * struct rcu_head - callback structure for use with RCU
> @@ -182,6 +183,27 @@ struct rcu_head {
> (p) = (v); \
> })
>
> +/* Infrastructure to implement the synchronize_() primitives. */
> +
> +struct rcu_synchronize {
> + struct rcu_head head;
> + struct completion completion;
> +};
> +
> +extern void wakeme_after_rcu(struct rcu_head *head);
> +
> +#define synchronize_rcu_xxx(name, func) \
> +void name(void) \
> +{ \
> + struct rcu_synchronize rcu; \
> + \
> + init_completion(&rcu.completion); \
> + /* Will wake me after RCU finished. */ \
> + func(&rcu.head, wakeme_after_rcu); \
> + /* Wait for it. */ \
> + wait_for_completion(&rcu.completion); \
> +}
> +
> /**
> * synchronize_sched - block until all CPUs have exited any non-preemptive
> * kernel code sequences.
> diff -urpNa -X dontdiff linux-2.6.25/include/linux/rcupreempt.h linux-2.6.25-C1-call_rcu_sched/include/linux/rcupreempt.h
> --- linux-2.6.25/include/linux/rcupreempt.h 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/include/linux/rcupreempt.h 2008-04-19 22:44:18.000000000 -0700
> @@ -42,10 +42,39 @@
> #include <linux/cpumask.h>
> #include <linux/seqlock.h>
>
> -#define rcu_qsctr_inc(cpu)
> +struct rcu_dyntick_sched {
> + int dynticks;
> + int dynticks_snap;
> + int sched_qs;
> + int sched_qs_snap;
> + int sched_dynticks_snap;
> +};
> +
> +DECLARE_PER_CPU(struct rcu_dyntick_sched, rcu_dyntick_sched);
> +
> +static inline void rcu_qsctr_inc(int cpu)
> +{
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + rdssp->sched_qs++;
> +}
> #define rcu_bh_qsctr_inc(cpu)
> #define call_rcu_bh(head, rcu) call_rcu(head, rcu)
>
> +/**
> + * call_rcu_sched - Queue RCU callback for invocation after sched grace period.
> + * @head: structure to be used for queueing the RCU updates.
> + * @func: actual update function to be invoked after the grace period
> + *
> + * The update function will be invoked some time after a full
> + * synchronize_sched()-style grace period elapses, in other words after
> + * all currently executing preempt-disabled sections of code (including
> + * hardirq handlers, NMI handlers, and local_irq_save() blocks) have
> + * completed.
> + */
> +extern void call_rcu_sched(struct rcu_head *head,
> + void (*func)(struct rcu_head *head));
> +
> extern void __rcu_read_lock(void) __acquires(RCU);
> extern void __rcu_read_unlock(void) __releases(RCU);
> extern int rcu_pending(int cpu);
> @@ -57,6 +86,7 @@ extern int rcu_needs_cpu(int cpu);
> extern void __synchronize_sched(void);
>
> extern void __rcu_init(void);
> +extern void rcu_init_sched(void);
> extern void rcu_check_callbacks(int cpu, int user);
> extern void rcu_restart_cpu(int cpu);
> extern long rcu_batches_completed(void);
> @@ -83,20 +113,20 @@ extern struct rcupreempt_trace *rcupreem
> struct softirq_action;
>
> #ifdef CONFIG_NO_HZ
> -DECLARE_PER_CPU(long, dynticks_progress_counter);
> +DECLARE_PER_CPU(struct rcu_dyntick_sched, dynticks_progress_counter);
^^^^^^^^^^^^^^^^^^^^^^^^^
Where is this defined? And why do we need it? We
already have rcu_dyntick_sched.dynticks for this purpose, no?
>
> static inline void rcu_enter_nohz(void)
> {
> smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
> - __get_cpu_var(dynticks_progress_counter)++;
> - WARN_ON(__get_cpu_var(dynticks_progress_counter) & 0x1);
> + __get_cpu_var(rcu_dyntick_sched).dynticks++;
> + WARN_ON(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1);
> }
>
> static inline void rcu_exit_nohz(void)
> {
> - __get_cpu_var(dynticks_progress_counter)++;
> + __get_cpu_var(rcu_dyntick_sched).dynticks++;
> smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
> - WARN_ON(!(__get_cpu_var(dynticks_progress_counter) & 0x1));
> + WARN_ON(!(__get_cpu_var(rcu_dyntick_sched).dynticks & 0x1));
> }
>
> #else /* CONFIG_NO_HZ */
> diff -urpNa -X dontdiff linux-2.6.25/include/linux/rcupreempt_trace.h linux-2.6.25-C1-call_rcu_sched/include/linux/rcupreempt_trace.h
> --- linux-2.6.25/include/linux/rcupreempt_trace.h 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/include/linux/rcupreempt_trace.h 2008-04-20 07:44:41.000000000 -0700
> @@ -66,12 +66,15 @@ struct rcupreempt_trace {
> long rcu_try_flip_m1;
> long rcu_try_flip_me1;
> long rcu_try_flip_m2;
> + int rcu_sched_cpu;
> };
>
> #ifdef CONFIG_RCU_TRACE
> -#define RCU_TRACE(fn, arg) fn(arg);
> +#define RCU_TRACE(fn, arg) fn(arg)
> +#define RCU_TRACE_1ARG(fn, arg, arg1) fn(arg, arg1)
> #else
> #define RCU_TRACE(fn, arg)
> +#define RCU_TRACE_1ARG(fn, arg, arg1)
> #endif
>
> extern void rcupreempt_trace_move2done(struct rcupreempt_trace *trace);
> @@ -94,6 +97,7 @@ extern void rcupreempt_trace_check_callb
> extern void rcupreempt_trace_done_remove(struct rcupreempt_trace *trace);
> extern void rcupreempt_trace_invoke(struct rcupreempt_trace *trace);
> extern void rcupreempt_trace_next_add(struct rcupreempt_trace *trace);
> +extern void rcusched_trace_grace_wait(struct rcupreempt_trace *trace, int cpu);
>
> #endif /* __KERNEL__ */
> #endif /* __LINUX_RCUPREEMPT_TRACE_H */
> diff -urpNa -X dontdiff linux-2.6.25/init/main.c linux-2.6.25-C1-call_rcu_sched/init/main.c
> --- linux-2.6.25/init/main.c 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/init/main.c 2008-04-17 08:10:33.000000000 -0700
> @@ -730,6 +730,7 @@ static void __init do_initcalls(void)
> */
> static void __init do_basic_setup(void)
> {
> + rcu_init_sched(); /* needed by module_init stage. */
> /* drivers will send hotplug events */
> init_workqueues();
> usermodehelper_init();
> diff -urpNa -X dontdiff linux-2.6.25/kernel/rcupdate.c linux-2.6.25-C1-call_rcu_sched/kernel/rcupdate.c
> --- linux-2.6.25/kernel/rcupdate.c 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/kernel/rcupdate.c 2008-04-17 08:10:33.000000000 -0700
> @@ -39,18 +39,12 @@
> #include <linux/sched.h>
> #include <asm/atomic.h>
> #include <linux/bitops.h>
> -#include <linux/completion.h>
> #include <linux/percpu.h>
> #include <linux/notifier.h>
> #include <linux/cpu.h>
> #include <linux/mutex.h>
> #include <linux/module.h>
>
> -struct rcu_synchronize {
> - struct rcu_head head;
> - struct completion completion;
> -};
> -
> static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
> static atomic_t rcu_barrier_cpu_count;
> static DEFINE_MUTEX(rcu_barrier_mutex);
> @@ -60,7 +54,7 @@ static struct completion rcu_barrier_com
> * Awaken the corresponding synchronize_rcu() instance now that a
> * grace period has elapsed.
> */
> -static void wakeme_after_rcu(struct rcu_head *head)
> +void wakeme_after_rcu(struct rcu_head *head)
> {
> struct rcu_synchronize *rcu;
>
> @@ -77,17 +71,7 @@ static void wakeme_after_rcu(struct rcu_
> * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
> * and may be nested.
> */
> -void synchronize_rcu(void)
> -{
> - struct rcu_synchronize rcu;
> -
> - init_completion(&rcu.completion);
> - /* Will wake me after RCU finished */
> - call_rcu(&rcu.head, wakeme_after_rcu);
> -
> - /* Wait for it */
> - wait_for_completion(&rcu.completion);
> -}
> +synchronize_rcu_xxx(synchronize_rcu, call_rcu)
> EXPORT_SYMBOL_GPL(synchronize_rcu);
>
> static void rcu_barrier_callback(struct rcu_head *notused)
> diff -urpNa -X dontdiff linux-2.6.25/kernel/rcupreempt.c linux-2.6.25-C1-call_rcu_sched/kernel/rcupreempt.c
> --- linux-2.6.25/kernel/rcupreempt.c 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/kernel/rcupreempt.c 2008-04-20 07:58:31.000000000 -0700
> @@ -46,6 +46,7 @@
> #include <asm/atomic.h>
> #include <linux/bitops.h>
> #include <linux/module.h>
> +#include <linux/kthread.h>
> #include <linux/completion.h>
> #include <linux/moduleparam.h>
> #include <linux/percpu.h>
> @@ -87,9 +88,14 @@ struct rcu_data {
> struct rcu_head **nexttail;
> struct rcu_head *waitlist[GP_STAGES];
> struct rcu_head **waittail[GP_STAGES];
> - struct rcu_head *donelist;
> + struct rcu_head *donelist; /* from waitlist & waitschedlist */
> struct rcu_head **donetail;
> long rcu_flipctr[2];
> + struct rcu_head *nextschedlist;
> + struct rcu_head **nextschedtail;
> + struct rcu_head *waitschedlist;
> + struct rcu_head **waitschedtail;
> + int rcu_sched_sleeping;
> #ifdef CONFIG_RCU_TRACE
> struct rcupreempt_trace trace;
> #endif /* #ifdef CONFIG_RCU_TRACE */
> @@ -131,11 +137,24 @@ enum rcu_try_flip_states {
> rcu_try_flip_waitmb_state,
> };
>
> +/*
> + * States for rcu_ctrlblk.rcu_sched_sleep.
^^^^^^^^^^^^^^^^^^^^^^^^^^^ should be
rcu_ctrlblk.sched_sleep
> + */
> +
> +enum rcu_sched_sleep_states {
> + rcu_sched_not_sleeping, /* Not sleeping, callbacks need GP. */
> + rcu_sched_sleep_prep, /* Thinking of sleeping, rechecking. */
> + rcu_sched_sleeping, /* Sleeping, awaken if GP needed. */
> +};
> +
> struct rcu_ctrlblk {
> spinlock_t fliplock; /* Protect state-machine transitions. */
> long completed; /* Number of last completed batch. */
> enum rcu_try_flip_states rcu_try_flip_state; /* The current state of
> the rcu state machine */
> + spinlock_t schedlock; /* Protect rcu_sched sleep state. */
> + enum rcu_sched_sleep_states sched_sleep; /* rcu_sched state. */
> + wait_queue_head_t sched_wq; /* Place for rcu_sched to sleep. */
> };
>
> static DEFINE_PER_CPU(struct rcu_data, rcu_data);
> @@ -143,8 +162,12 @@ static struct rcu_ctrlblk rcu_ctrlblk =
> .fliplock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.fliplock),
> .completed = 0,
> .rcu_try_flip_state = rcu_try_flip_idle_state,
> + .schedlock = __SPIN_LOCK_UNLOCKED(rcu_ctrlblk.schedlock),
> + .sched_sleep = rcu_sched_not_sleeping,
> + .sched_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rcu_ctrlblk.sched_wq),
> };
>
> +static struct task_struct *rcu_sched_grace_period_task;
>
> #ifdef CONFIG_RCU_TRACE
> static char *rcu_try_flip_state_names[] =
> @@ -194,6 +217,7 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(enu
> * cached in a local variable, but where the CPU number is so cached.
> */
> #define RCU_TRACE_CPU(f, cpu) RCU_TRACE(f, &(RCU_DATA_CPU(cpu)->trace));
> +#define RCU_TRACE_1ARG_CPU(f, cpu, a) RCU_TRACE_1ARG(f, &(RCU_DATA_CPU(cpu)->trace), a);
>
> /*
> * Helper macro for tracing when the appropriate rcu_data is not
> @@ -207,6 +231,8 @@ static DEFINE_PER_CPU_SHARED_ALIGNED(enu
> */
> #define RCU_TRACE_RDP(f, rdp) RCU_TRACE(f, &((rdp)->trace));
>
> +#define RCU_SCHED_BATCH_TIME (HZ / 50)
> +
> /*
> * Return the number of RCU batches processed thus far. Useful
> * for debug and statistics.
> @@ -413,32 +439,34 @@ static void __rcu_advance_callbacks(stru
> }
> }
>
> -#ifdef CONFIG_NO_HZ
> +DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_dyntick_sched, rcu_dyntick_sched) = {
> + .dynticks = 1,
> +};
>
> -DEFINE_PER_CPU(long, dynticks_progress_counter) = 1;
> -static DEFINE_PER_CPU(long, rcu_dyntick_snapshot);
> +#ifdef CONFIG_NO_HZ
> static DEFINE_PER_CPU(int, rcu_update_flag);
>
> /**
> * rcu_irq_enter - Called from Hard irq handlers and NMI/SMI.
> *
> * If the CPU was idle with dynamic ticks active, this updates the
> - * dynticks_progress_counter to let the RCU handling know that the
> + * rcu_dyntick_sched.dynticks to let the RCU handling know that the
> * CPU is active.
> */
> void rcu_irq_enter(void)
> {
> int cpu = smp_processor_id();
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
>
> if (per_cpu(rcu_update_flag, cpu))
> per_cpu(rcu_update_flag, cpu)++;
>
> /*
> * Only update if we are coming from a stopped ticks mode
> - * (dynticks_progress_counter is even).
> + * (rcu_dyntick_sched.dynticks is even).
> */
> if (!in_interrupt() &&
> - (per_cpu(dynticks_progress_counter, cpu) & 0x1) == 0) {
> + (rdssp->dynticks & 0x1) == 0) {
> /*
> * The following might seem like we could have a race
> * with NMI/SMIs. But this really isn't a problem.
> @@ -461,12 +489,12 @@ void rcu_irq_enter(void)
> * RCU read-side critical sections on this CPU would
> * have already completed.
> */
> - per_cpu(dynticks_progress_counter, cpu)++;
> + rdssp->dynticks++;
> /*
> * The following memory barrier ensures that any
> * rcu_read_lock() primitives in the irq handler
> * are seen by other CPUs to follow the above
> - * increment to dynticks_progress_counter. This is
> + * increment to rcu_dyntick_sched.dynticks. This is
> * required in order for other CPUs to correctly
> * determine when it is safe to advance the RCU
> * grace-period state machine.
> @@ -474,7 +502,7 @@ void rcu_irq_enter(void)
> smp_mb(); /* see above block comment. */
> /*
> * Since we can't determine the dynamic tick mode from
> - * the dynticks_progress_counter after this routine,
> + * the rcu_dyntick_sched.dynticks after this routine,
> * we use a second flag to acknowledge that we came
> * from an idle state with ticks stopped.
> */
> @@ -482,7 +510,7 @@ void rcu_irq_enter(void)
> /*
> * If we take an NMI/SMI now, they will also increment
> * the rcu_update_flag, and will not update the
> - * dynticks_progress_counter on exit. That is for
> + * rcu_dyntick_sched.dynticks on exit. That is for
> * this IRQ to do.
> */
> }
> @@ -492,12 +520,13 @@ void rcu_irq_enter(void)
> * rcu_irq_exit - Called from exiting Hard irq context.
> *
> * If the CPU was idle with dynamic ticks active, update the
> - * dynticks_progress_counter to put let the RCU handling be
> + * rcu_dyntick_sched.dynticks to put let the RCU handling be
> * aware that the CPU is going back to idle with no ticks.
> */
> void rcu_irq_exit(void)
> {
> int cpu = smp_processor_id();
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
>
> /*
> * rcu_update_flag is set if we interrupted the CPU
> @@ -505,7 +534,7 @@ void rcu_irq_exit(void)
> * Once this occurs, we keep track of interrupt nesting
> * because a NMI/SMI could also come in, and we still
> * only want the IRQ that started the increment of the
> - * dynticks_progress_counter to be the one that modifies
> + * rcu_dyntick_sched.dynticks to be the one that modifies
> * it on exit.
> */
> if (per_cpu(rcu_update_flag, cpu)) {
> @@ -517,28 +546,29 @@ void rcu_irq_exit(void)
>
> /*
> * If an NMI/SMI happens now we are still
> - * protected by the dynticks_progress_counter being odd.
> + * protected by the rcu_dyntick_sched.dynticks being odd.
> */
>
> /*
> * The following memory barrier ensures that any
> * rcu_read_unlock() primitives in the irq handler
> * are seen by other CPUs to preceed the following
> - * increment to dynticks_progress_counter. This
> + * increment to rcu_dyntick_sched.dynticks. This
> * is required in order for other CPUs to determine
> * when it is safe to advance the RCU grace-period
> * state machine.
> */
> smp_mb(); /* see above block comment. */
> - per_cpu(dynticks_progress_counter, cpu)++;
> - WARN_ON(per_cpu(dynticks_progress_counter, cpu) & 0x1);
> + rdssp->dynticks++;
> + WARN_ON(rdssp->dynticks & 0x1);
> }
> }
>
> static void dyntick_save_progress_counter(int cpu)
> {
> - per_cpu(rcu_dyntick_snapshot, cpu) =
> - per_cpu(dynticks_progress_counter, cpu);
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + rdssp->dynticks_snap = rdssp->dynticks;
> }
>
> static inline int
> @@ -546,9 +576,10 @@ rcu_try_flip_waitack_needed(int cpu)
> {
> long curr;
> long snap;
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
>
> - curr = per_cpu(dynticks_progress_counter, cpu);
> - snap = per_cpu(rcu_dyntick_snapshot, cpu);
> + curr = rdssp->dynticks;
> + snap = rdssp->dynticks_snap;
> smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
>
> /*
> @@ -582,9 +613,10 @@ rcu_try_flip_waitmb_needed(int cpu)
> {
> long curr;
> long snap;
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
>
> - curr = per_cpu(dynticks_progress_counter, cpu);
> - snap = per_cpu(rcu_dyntick_snapshot, cpu);
> + curr = rdssp->dynticks;
> + snap = rdssp->dynticks_snap;
> smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
>
> /*
> @@ -611,14 +643,85 @@ rcu_try_flip_waitmb_needed(int cpu)
> return 1;
> }
>
> +static void dyntick_save_progress_counter_sched(int cpu)
> +{
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + rdssp->sched_dynticks_snap = rdssp->dynticks;
> +}
> +
> +static int rcu_qsctr_inc_needed_dyntick(int cpu)
> +{
> + long curr;
> + long snap;
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + curr = rdssp->dynticks;
> + snap = rdssp->sched_dynticks_snap;
> + smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
> +
> + /*
> + * If the CPU remained in dynticks mode for the entire time
> + * and didn't take any interrupts, NMIs, SMIs, or whatever,
> + * then it cannot be in the middle of an preempt-disabled
> + * region of code. Therefore, this CPU has been in a quiescent
> + * state the entire time, and we don't need to wait for it.
> + */
> +
> + if ((curr == snap) && ((curr & 0x1) == 0))
> + return 0;
> +
> + /*
> + * If the CPU passed through or entered a dynticks idle phase with
> + * no active irq handlers, then, as above, this CPU has already
> + * passed through a quiescent state.
> + */
> +
> + if ((curr - snap) > 2 || (snap & 0x1) == 0)
> + return 0;
> +
> + /* We need this CPU to go through a quiescent state. */
> +
> + return 1;
> +}
> +
> #else /* !CONFIG_NO_HZ */
>
> -# define dyntick_save_progress_counter(cpu) do { } while (0)
> -# define rcu_try_flip_waitack_needed(cpu) (1)
> -# define rcu_try_flip_waitmb_needed(cpu) (1)
> +# define dyntick_save_progress_counter(cpu) do { } while (0)
> +# define rcu_try_flip_waitack_needed(cpu) (1)
> +# define rcu_try_flip_waitmb_needed(cpu) (1)
> +
> +# define dyntick_save_progress_counter_sched(cpu) do { } while (0)
> +# define rcu_qsctr_inc_needed_dyntick(cpu) (1)
>
> #endif /* CONFIG_NO_HZ */
>
> +static void save_qsctr_sched(int cpu)
> +{
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + rdssp->sched_qs_snap = rdssp->sched_qs;
> +}
> +
> +static inline int rcu_qsctr_inc_needed(int cpu)
> +{
> + struct rcu_dyntick_sched *rdssp = &per_cpu(rcu_dyntick_sched, cpu);
> +
> + /*
> + * If there has been a quiescent state, no more need to wait
> + * on this CPU.
> + */
> +
> + if (rdssp->sched_qs != rdssp->sched_qs_snap) {
> + smp_mb(); /* force ordering with cpu entering schedule(). */
> + return 0;
> + }
> +
> + /* We need this CPU to go through a quiescent state. */
> +
> + return 1;
> +}
> +
> /*
> * Get here when RCU is idle. Decide whether we need to
> * move out of idle state, and return non-zero if so.
> @@ -821,6 +924,26 @@ void rcu_check_callbacks(int cpu, int us
> unsigned long flags;
> struct rcu_data *rdp = RCU_DATA_CPU(cpu);
>
> + /*
> + * If this CPU took its interrupt from user mode or from the
> + * idle loop, and this is not a nested interrupt, then
> + * this CPU has to have exited all prior preept-disable
> + * sections of code. So increment the counter to note this.
> + *
> + * The memory barrier is needed to handle the case where
> + * writes from a preempt-disable section of code get reordered
> + * into schedule() by this CPU's write buffer. So the memory
> + * barrier makes sure that the rcu_qsctr_inc() is seen by other
> + * CPUs to happen after any such write.
> + */
> +
> + if (user ||
> + (idle_cpu(cpu) && !in_softirq() &&
> + hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
> + smp_mb(); /* Guard against aggressive schedule(). */
> + rcu_qsctr_inc(cpu);
> + }
> +
> rcu_check_mb(cpu);
> if (rcu_ctrlblk.completed == rdp->completed)
> rcu_try_flip();
> @@ -871,6 +994,8 @@ void rcu_offline_cpu(int cpu)
> struct rcu_head *list = NULL;
> unsigned long flags;
> struct rcu_data *rdp = RCU_DATA_CPU(cpu);
> + struct rcu_head *schedlist = NULL;
> + struct rcu_head **schedtail = &schedlist;
> struct rcu_head **tail = &list;
>
> /*
> @@ -884,6 +1009,11 @@ void rcu_offline_cpu(int cpu)
> rcu_offline_cpu_enqueue(rdp->waitlist[i], rdp->waittail[i],
> list, tail);
> rcu_offline_cpu_enqueue(rdp->nextlist, rdp->nexttail, list, tail);
> + rcu_offline_cpu_enqueue(rdp->waitschedlist, rdp->waitschedtail,
> + schedlist, schedtail);
> + rcu_offline_cpu_enqueue(rdp->nextschedlist, rdp->nextschedtail,
> + schedlist, schedtail);
> + rdp->rcu_sched_sleeping = 0;
> spin_unlock_irqrestore(&rdp->lock, flags);
> rdp->waitlistcount = 0;
>
> @@ -918,22 +1048,40 @@ void rcu_offline_cpu(int cpu)
> * fix.
> */
>
> - local_irq_save(flags);
> + local_irq_save(flags); /* disable preempt till we know what lock. */
> rdp = RCU_DATA_ME();
> spin_lock(&rdp->lock);
> *rdp->nexttail = list;
> if (list)
> rdp->nexttail = tail;
> + *rdp->nextschedtail = schedlist;
> + if (schedlist)
> + rdp->nextschedtail = schedtail;
> spin_unlock_irqrestore(&rdp->lock, flags);
> }
>
> void __devinit rcu_online_cpu(int cpu)
> {
> unsigned long flags;
> + struct rcu_data *rdp;
>
> spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
> cpu_set(cpu, rcu_cpu_online_map);
> spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
> +
> + /*
> + * The rcu_sched grace-period processing might have bypassed
> + * this CPU, given that it was not in the rcu_cpu_online_map
> + * when the grace-period scan started. This means that the
> + * grace-period task might sleep. So make sure that if this
> + * should happen, the first callback posted to this CPU will
> + * wake up the grace-period task if need be.
> + */
> +
> + rdp = RCU_DATA_CPU(cpu);
> + spin_lock_irqsave(&rdp->lock, flags);
> + rdp->rcu_sched_sleeping = 1;
> + spin_unlock_irqrestore(&rdp->lock, flags);
> }
>
> #else /* #ifdef CONFIG_HOTPLUG_CPU */
> @@ -988,31 +1136,215 @@ void call_rcu(struct rcu_head *head, voi
> *rdp->nexttail = head;
> rdp->nexttail = &head->next;
> RCU_TRACE_RDP(rcupreempt_trace_next_add, rdp);
> - spin_unlock(&rdp->lock);
> - local_irq_restore(flags);
> + spin_unlock_irqrestore(&rdp->lock, flags);
> }
> EXPORT_SYMBOL_GPL(call_rcu);
>
> +void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
> +{
> + unsigned long flags;
> + struct rcu_data *rdp;
> + int wake_gp = 0;
> +
> + head->func = func;
> + head->next = NULL;
> + local_irq_save(flags);
> + rdp = RCU_DATA_ME();
> + spin_lock(&rdp->lock);
> + *rdp->nextschedtail = head;
> + rdp->nextschedtail = &head->next;
> + if (rdp->rcu_sched_sleeping) {
> +
> + /* Grace-period processing might be sleeping... */
> +
> + rdp->rcu_sched_sleeping = 0;
> + wake_gp = 1;
> + }
> + spin_unlock_irqrestore(&rdp->lock, flags);
> + if (wake_gp) {
> +
> + /* Wake up grace-period processing, unless someone beat us. */
> +
> + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
> + if (rcu_ctrlblk.sched_sleep != rcu_sched_sleeping)
> + wake_gp = 0;
> + rcu_ctrlblk.sched_sleep = rcu_sched_not_sleeping;
> + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
> + if (wake_gp)
> + wake_up_interruptible(&rcu_ctrlblk.sched_wq);
> + }
> +}
> +EXPORT_SYMBOL_GPL(call_rcu_sched);
> +
> /*
> * Wait until all currently running preempt_disable() code segments
> * (including hardware-irq-disable segments) complete. Note that
> * in -rt this does -not- necessarily result in all currently executing
> * interrupt -handlers- having completed.
> */
> -void __synchronize_sched(void)
> +synchronize_rcu_xxx(__synchronize_sched, call_rcu_sched)
> +EXPORT_SYMBOL_GPL(__synchronize_sched);
> +
> +/*
> + * kthread function that manages call_rcu_sched grace periods.
> + */
> +static int rcu_sched_grace_period(void *arg)
> {
> - cpumask_t oldmask;
> + int couldsleep; /* might sleep after current pass. */
> + int couldsleepnext = 0; /* might sleep after next pass. */
> int cpu;
> + unsigned long flags;
> + cpumask_t cpu_snap;
> + struct rcu_data *rdp;
> + int ret;
>
> - if (sched_getaffinity(0, &oldmask) < 0)
> - oldmask = cpu_possible_map;
> - for_each_online_cpu(cpu) {
> - sched_setaffinity(0, cpumask_of_cpu(cpu));
> - schedule();
> - }
> - sched_setaffinity(0, oldmask);
> + /*
> + * Each pass through the following loop handles one
> + * rcu_sched grace period cycle.
> + */
> + do {
> + /* Save each CPU's current state. */
> +
> + spin_lock_irqsave(&rcu_ctrlblk.fliplock, flags);
> + cpu_snap = cpu_online_map;
> + spin_unlock_irqrestore(&rcu_ctrlblk.fliplock, flags);
> + for_each_cpu_mask(cpu, cpu_snap) {
> + if (cpu_is_offline(cpu)) {
> + cpu_clear(cpu, cpu_snap);
> + continue;
> + }
> + dyntick_save_progress_counter_sched(cpu);
> + save_qsctr_sched(cpu);
> + if (cpu_is_offline(cpu))
> + cpu_clear(cpu, cpu_snap);
> + }
> +
> + /*
> + * Sleep for about an RCU grace-period's worth to
> + * allow better batching and to consume less CPU.
> + */
> + schedule_timeout_interruptible(RCU_SCHED_BATCH_TIME);
> +
> + /*
> + * If there was nothing to do last time, prepare to
> + * sleep at the end of the current grace period cycle.
> + */
> + couldsleep = couldsleepnext;
> + couldsleepnext = 1;
> + if (couldsleep) {
> + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
> + rcu_ctrlblk.sched_sleep = rcu_sched_sleep_prep;
> + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
> + }
> +
> + /*
> + * Wait on each CPU in turn to have either visited
> + * a quiescent state or been in dynticks-idle mode.
> + */
> + for_each_cpu_mask(cpu, cpu_snap) {
> + RCU_TRACE_1ARG_CPU(rcusched_trace_grace_wait, 0, cpu);
> + while (rcu_qsctr_inc_needed(cpu) &&
> + rcu_qsctr_inc_needed_dyntick(cpu)) {
> + if (cpu_is_offline(cpu)) {
> + cpu_clear(cpu, cpu_snap);
> + break;
> + }
> + /* resched_cpu(cpu); @@@ */
> + schedule_timeout_interruptible(1);
> + }
> + RCU_TRACE_1ARG_CPU(rcusched_trace_grace_wait, 0, -1);
> + }
> +
> + /* Advance callbacks for each CPU. */
> +
> + for_each_cpu_mask(cpu, cpu_snap) {
> + rdp = RCU_DATA_CPU(cpu);
> + spin_lock_irqsave(&rdp->lock, flags);
> + if (cpu_is_offline(cpu)) {
> + spin_unlock_irqrestore(&rdp->lock, flags);
> + continue;
> + }
> +
> + /*
> + * We are running on this CPU irq-disabled, so no
> + * CPU can go offline until we re-enable irqs.
> + * The current CPU might have already gone
> + * offline (between the for_each_offline_cpu and
^^^^^^^^^^^^^^^^^^^^
for_each_cpu_mask().
Infact, for_each_offline_cpu() doesn't even exist ;-)
I guess doing the multiple cpu_is_offline() checks is unavoidable,
unless we use get_online_cpus()/put_online_cpus(). But that's an
overkill in this context.
So, looks okay to me.
> + * the spin_lock_irqsave), but in that case all its
> + * callback lists will be empty, so no harm done.
> + *
> + * Advance the callbacks! We share normal RCU's
> + * donelist, since callbacks are invoked the
> + * same way in either case.
> + */
> + if (rdp->waitschedlist != NULL) {
> + *rdp->donetail = rdp->waitschedlist;
> + rdp->donetail = rdp->waitschedtail;
> +
> + /*
> + * Next rcu_check_callbacks() will
> + * do the required raise_softirq().
> + */
> + }
> + if (rdp->nextschedlist != NULL) {
> + rdp->waitschedlist = rdp->nextschedlist;
> + rdp->waitschedtail = rdp->nextschedtail;
> + couldsleep = 0;
> + couldsleepnext = 0;
> + } else {
> + rdp->waitschedlist = NULL;
> + rdp->waitschedtail = &rdp->waitschedlist;
> + }
> + rdp->nextschedlist = NULL;
> + rdp->nextschedtail = &rdp->nextschedlist;
> +
> + /* Mark sleep intention. */
> +
> + rdp->rcu_sched_sleeping = couldsleep;
> +
> + spin_unlock_irqrestore(&rdp->lock, flags);
> + }
> +
> + /* If we saw callbacks on the last scan, go deal with them. */
> +
> + if (!couldsleep)
> + continue;
> +
> + /* Attempt to block... */
> +
> + spin_lock_irqsave(&rcu_ctrlblk.schedlock, flags);
> + if (rcu_ctrlblk.sched_sleep != rcu_sched_sleep_prep) {
> +
> + /*
> + * Someone posted a callback after we scanned.
> + * Go take care of it.
> + */
> + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
> + couldsleepnext = 0;
> + continue;
> + }
> +
> + /* Block until the next person posts a callback. */
> +
> + rcu_ctrlblk.sched_sleep = rcu_sched_sleeping;
> + spin_unlock_irqrestore(&rcu_ctrlblk.schedlock, flags);
> + ret = 0;
> + __wait_event_interruptible(rcu_ctrlblk.sched_wq,
> + rcu_ctrlblk.sched_sleep != rcu_sched_sleeping,
> + ret);
> +
> + /*
> + * Signals would prevent us from sleeping, and we cannot
> + * do much with them in any case. So flush them.
> + */
> + if (ret)
> + flush_signals(current);
> + couldsleepnext = 0;
> +
> + } while (!kthread_should_stop());
> +
> + return (0);
> }
> -EXPORT_SYMBOL_GPL(__synchronize_sched);
>
> /*
> * Check to see if any future RCU-related work will need to be done
> @@ -1029,7 +1361,9 @@ int rcu_needs_cpu(int cpu)
>
> return (rdp->donelist != NULL ||
> !!rdp->waitlistcount ||
> - rdp->nextlist != NULL);
> + rdp->nextlist != NULL ||
> + rdp->nextschedlist != NULL ||
> + rdp->waitschedlist != NULL);
> }
>
> int rcu_pending(int cpu)
> @@ -1040,7 +1374,9 @@ int rcu_pending(int cpu)
>
> if (rdp->donelist != NULL ||
> !!rdp->waitlistcount ||
> - rdp->nextlist != NULL)
> + rdp->nextlist != NULL ||
> + rdp->nextschedlist != NULL ||
> + rdp->waitschedlist != NULL)
> return 1;
>
> /* The RCU core needs an acknowledgement from this CPU. */
> @@ -1107,6 +1443,11 @@ void __init __rcu_init(void)
> rdp->donetail = &rdp->donelist;
> rdp->rcu_flipctr[0] = 0;
> rdp->rcu_flipctr[1] = 0;
> + rdp->nextschedlist = NULL;
> + rdp->nextschedtail = &rdp->nextschedlist;
> + rdp->waitschedlist = NULL;
> + rdp->waitschedtail = &rdp->waitschedlist;
> + rdp->rcu_sched_sleeping = 0;
> }
> register_cpu_notifier(&rcu_nb);
>
> @@ -1129,11 +1470,15 @@ void __init __rcu_init(void)
> }
>
> /*
> - * Deprecated, use synchronize_rcu() or synchronize_sched() instead.
> + * Late-boot-time RCU initialization that must wait until after scheduler
> + * has been initialized.
> */
> -void synchronize_kernel(void)
> +void __init rcu_init_sched(void)
> {
> - synchronize_rcu();
> + rcu_sched_grace_period_task = kthread_run(rcu_sched_grace_period,
> + NULL,
> + "rcu_sched_grace_period");
> + WARN_ON(IS_ERR(rcu_sched_grace_period_task));
> }
>
> #ifdef CONFIG_RCU_TRACE
> diff -urpNa -X dontdiff linux-2.6.25/kernel/rcupreempt_trace.c linux-2.6.25-C1-call_rcu_sched/kernel/rcupreempt_trace.c
> --- linux-2.6.25/kernel/rcupreempt_trace.c 2008-04-16 19:49:44.000000000 -0700
> +++ linux-2.6.25-C1-call_rcu_sched/kernel/rcupreempt_trace.c 2008-04-21 15:45:07.000000000 -0700
> @@ -134,6 +134,10 @@ void rcupreempt_trace_next_add(struct rc
> trace->next_add++;
> trace->next_length++;
> }
> +void rcusched_trace_grace_wait(struct rcupreempt_trace *trace, int cpu)
> +{
> + trace->rcu_sched_cpu = cpu;
> +}
>
> static void rcupreempt_trace_sum(struct rcupreempt_trace *sp)
> {
> @@ -262,6 +266,38 @@ static ssize_t rcuctrs_read(struct file
> return bcount;
> }
>
> +static ssize_t rcuschedstat_read(struct file *filp, char __user *buffer,
> + size_t count, loff_t *ppos)
> +{
> + int cnt = 0;
> + int cpu = rcupreempt_trace_cpu(0)->rcu_sched_cpu;
> + ssize_t bcount;
> +
> + mutex_lock(&rcupreempt_trace_mutex);
> +
> + cnt += snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
> + "CPU: %d ", cpu);
> + if (cpu != -1) {
> + struct rcu_dyntick_sched *rdsp;
> +
> + rdsp = &per_cpu(rcu_dyntick_sched, cpu);
> + cnt += snprintf(&rcupreempt_trace_buf[cnt],
> + RCUPREEMPT_TRACE_BUF_SIZE - cnt,
> + "dynticks: %d %d qs %d %d",
> + rdsp->dynticks,
> + rdsp->sched_dynticks_snap,
> + rdsp->sched_qs,
> + rdsp->sched_qs_snap);
> + }
> + cnt += snprintf(&rcupreempt_trace_buf[cnt],
> + RCUPREEMPT_TRACE_BUF_SIZE - cnt,
> + "\n");
> + bcount = simple_read_from_buffer(buffer, count, ppos,
> + rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
> + mutex_unlock(&rcupreempt_trace_mutex);
> + return bcount;
> +}
> +
> static struct file_operations rcustats_fops = {
> .owner = THIS_MODULE,
> .read = rcustats_read,
> @@ -277,7 +313,12 @@ static struct file_operations rcuctrs_fo
> .read = rcuctrs_read,
> };
>
> -static struct dentry *rcudir, *statdir, *ctrsdir, *gpdir;
> +static struct file_operations rcuschedstat_fops = {
> + .owner = THIS_MODULE,
> + .read = rcuschedstat_read,
> +};
> +
> +static struct dentry *rcudir, *statdir, *ctrsdir, *gpdir, *schedstatdir;
> static int rcupreempt_debugfs_init(void)
> {
> rcudir = debugfs_create_dir("rcu", NULL);
> @@ -296,12 +337,19 @@ static int rcupreempt_debugfs_init(void)
> NULL, &rcuctrs_fops);
> if (!ctrsdir)
> goto free_out;
> +
> + schedstatdir = debugfs_create_file("schedstat", 0444, rcudir,
> + NULL, &rcuschedstat_fops);
> + if (!schedstatdir)
> + goto free_out;
> return 0;
> free_out:
> if (statdir)
> debugfs_remove(statdir);
> if (gpdir)
> debugfs_remove(gpdir);
> + if (ctrsdir)
> + debugfs_remove(ctrsdir);
> debugfs_remove(rcudir);
> out:
> return 1;
> @@ -309,11 +357,16 @@ out:
>
> static int __init rcupreempt_trace_init(void)
> {
> + int ret;
> +
> mutex_init(&rcupreempt_trace_mutex);
> rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL);
> if (!rcupreempt_trace_buf)
> return 1;
> - return rcupreempt_debugfs_init();
> + ret = rcupreempt_debugfs_init();
> + if (ret)
> + kfree(rcupreempt_trace_buf);
> + return ret;
> }
>
> static void __exit rcupreempt_trace_cleanup(void)
> @@ -322,6 +375,7 @@ static void __exit rcupreempt_trace_clea
> debugfs_remove(gpdir);
> debugfs_remove(ctrsdir);
> debugfs_remove(rcudir);
> + debugfs_remove(schedstatdir);
> kfree(rcupreempt_trace_buf);
> }
--
Thanks and Regards
gautham
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