> rcu_bh: cur=-287 completed=-287 pending=0 s=0
>
> online: 0-7
>
> The first two lines are for rcu, the second two for rcu_bh. The cur=
> is the current grace-period number, and the completed= is the number
> of the last completed grace period. If these two numbers are equal,
> the corresponding flavor of RCU is idle. The pending= is the furthest
> future batch number that is required, if equal to cur=, no additional
> grace periods are required. The s=, if non-zero, indicates that a round
> of reschedule IPIs has been send to attempt to expedite the current
> grace period.
>
> The second and fourth lines are a comma/dash-separated list of
> the CPUs that have not yet reported a quiescent state for the
> current grace period (CPUs 0, 3, and 7 for "rcu" above).
>
> The last line lists the online CPUs.
>
>
> Reading from the "rcu/rcudata" file results in the following:
>
> rcu:
> 0 qb=885 b=884 pq=1 qsp=0 ql=0 bl=10
> 1 qb=885 b=882 pq=1 qsp=0 ql=2 bl=10
> 2 qb=885 b=854 pq=1 qsp=0 ql=0 bl=10
> 3 qb=885 b=885 pq=1 qsp=0 ql=0 bl=10
> rcu_bh:
> 0 qb=-291 b=-291 pq=1 qsp=0 ql=0 bl=10
> 1 qb=-291 b=0 pq=1 qsp=0 ql=0 bl=10
> 2 qb=-291 b=0 pq=1 qsp=0 ql=0 bl=10
> 3 qb=-291 b=-298 pq=1 qsp=0 ql=0 bl=10
>
> This output is again split into rcu and rcu_bh portions. Within each
> portion, there is one line per CPU, but only for those CPUs that have
> been online at least once since boot. The number at the beginning of
> each line is the CPU number, followed by an "!" if the corresponding CPU
> is currently offline. The qb= is the batch number for the RCU core,
> the b= is the batch number corresponding to the callbacks waiting for
> the current grace period for this CPU, the pq= is a flag indicating that
> this CPU has passed through a quiescent state for the current grace
> period, the qsp= is a flag indicating that the RCU core has been
> informed that this CPU has passed through a quiescent state for the
> current grace period, the ql= is the number of RCU callbacks currently
> enqueued on this CPU (regardless of their state), and the bl= is the
> current limit of the number of callbacks to be invoked at one shot.
>
> Tested on x86 and Power, rebased to -tip.
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>
> include/linux/rcuclassic.h | 4 +
> kernel/Kconfig.preempt | 1
> kernel/Makefile | 2
> kernel/rcuclassic.c | 5 -
> kernel/rcuclassic_trace.c | 179 +++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 188 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
> index 5f89b62..ce183a8 100644
> --- a/include/linux/rcuclassic.h
> +++ b/include/linux/rcuclassic.h
> @@ -63,6 +63,9 @@ struct rcu_ctrlblk {
> /* for current batch to proceed. */
> } ____cacheline_internodealigned_in_smp;
>
> +extern struct rcu_ctrlblk rcu_ctrlblk;
> +extern struct rcu_ctrlblk rcu_bh_ctrlblk;
> +
> /* Is batch a before batch b ? */
> static inline int rcu_batch_before(long a, long b)
> {
> @@ -81,6 +84,7 @@ struct rcu_data {
> long quiescbatch; /* Batch # for grace period */
> int passed_quiesc; /* User-mode/idle loop etc. */
> int qs_pending; /* core waits for quiesc state */
> + bool beenonline; /* CPU online at least once */
>
> /* 2) batch handling */
> /*
> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index 9fdba03..ba32338 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -68,7 +68,6 @@ config PREEMPT_RCU
>
> config RCU_TRACE
> bool "Enable tracing for RCU - currently stats in debugfs"
> - depends on PREEMPT_RCU
> select DEBUG_FS
> default y
> help
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 4e1d7df..e0bfce7 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -77,6 +77,8 @@ obj-$(CONFIG_CLASSIC_RCU) += rcuclassic.o
> obj-$(CONFIG_PREEMPT_RCU) += rcupreempt.o
> ifeq ($(CONFIG_PREEMPT_RCU),y)
> obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
> +else
> +obj-$(CONFIG_RCU_TRACE) += rcuclassic_trace.o
> endif
> obj-$(CONFIG_RELAY) += relay.o
> obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
> diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
> index 37f72e5..54bd23b 100644
> --- a/kernel/rcuclassic.c
> +++ b/kernel/rcuclassic.c
> @@ -58,14 +58,14 @@ EXPORT_SYMBOL_GPL(rcu_lock_map);
>
>
> /* Definition for rcupdate control block. */
> -static struct rcu_ctrlblk rcu_ctrlblk = {
> +struct rcu_ctrlblk rcu_ctrlblk = {
> .cur = -300,
> .completed = -300,
> .pending = -300,
> .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
> .cpumask = CPU_MASK_NONE,
> };
> -static struct rcu_ctrlblk rcu_bh_ctrlblk = {
> +struct rcu_ctrlblk rcu_bh_ctrlblk = {
> .cur = -300,
> .completed = -300,
> .pending = -300,
> @@ -725,6 +725,7 @@ static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
> rdp->donetail = &rdp->donelist;
> rdp->quiescbatch = rcp->completed;
> rdp->qs_pending = 0;
> + rdp->beenonline = 1;
> rdp->cpu = cpu;
> rdp->blimit = blimit;
> spin_unlock_irqrestore(&rcp->lock, flags);
> diff --git a/kernel/rcuclassic_trace.c b/kernel/rcuclassic_trace.c
> new file mode 100644
> index 0000000..d19780b
> --- /dev/null
> +++ b/kernel/rcuclassic_trace.c
> @@ -0,0 +1,179 @@
> +/*
> + * Read-Copy Update tracing for classic implementation
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software
> + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> + *
> + * Copyright IBM Corporation, 2008
> + *
> + * Papers:
http://www.rdrop.com/users/paulmck/RCU
> + *
> + * For detailed explanation of Read-Copy Update mechanism see -
> + * Documentation/RCU
> + *
> + */
> +#include <linux/types.h>
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +#include <linux/spinlock.h>
> +#include <linux/smp.h>
> +#include <linux/rcupdate.h>
> +#include <linux/interrupt.h>
> +#include <linux/sched.h>
> +#include <asm/atomic.h>
> +#include <linux/bitops.h>
> +#include <linux/module.h>
> +#include <linux/completion.h>
> +#include <linux/moduleparam.h>
> +#include <linux/percpu.h>
> +#include <linux/notifier.h>
> +#include <linux/cpu.h>
> +#include <linux/mutex.h>
> +#include <linux/debugfs.h>
> +
> +static DEFINE_MUTEX(rcuclassic_trace_mutex);
> +static char *rcuclassic_trace_buf;
> +#define RCUCLASSIC_TRACE_BUF_SIZE (128 * num_possible_cpus() + 100)
> +
> +static int print_one_rcu_data(struct rcu_data *rdp, char *buf, char *ebuf)
> +{
> + int cnt = 0;
> +
> + if (!rdp->beenonline)
> + return 0;
> + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt],
> + "%3d%cqb=%ld b=%ld pq=%d qsp=%d ql=%ld bl=%ld\n",
> + rdp->cpu, cpu_is_offline(rdp->cpu) ? '!' : ' ',
> + rdp->quiescbatch, rdp->batch, rdp->passed_quiesc,
> + rdp->qs_pending, rdp->qlen, rdp->blimit);
> + return cnt;
> +}
> +
> +#define PRINT_RCU_DATA(name, buf, ebuf) \
> + do { \
> + int _p_r_d_i; \
> + \
> + for_each_possible_cpu(_p_r_d_i) \
> + (buf) += print_one_rcu_data(&per_cpu(name, _p_r_d_i), \
> + buf, ebuf); \
> + } while (0)
> +
> +static ssize_t rcudata_read(struct file *filp, char __user *buffer,
> + size_t count, loff_t *ppos)
> +{
> + ssize_t bcount;
> + char *buf = rcuclassic_trace_buf;
> + char *ebuf = &rcuclassic_trace_buf[RCUCLASSIC_TRACE_BUF_SIZE];
> +
> + mutex_lock(&rcuclassic_trace_mutex);
> + buf += snprintf(buf, ebuf - buf, "rcu:\n");
> + PRINT_RCU_DATA(rcu_data, buf, ebuf);
> + buf += snprintf(buf, ebuf - buf, "rcu_bh:\n");
> + PRINT_RCU_DATA(rcu_bh_data, buf, ebuf);
> + bcount = simple_read_from_buffer(buffer, count, ppos,
> + rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
