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    SubjectRe: [PATCH] v3 rudimentary tracing for Classic RCU
    On Tue, Oct 14, 2008 at 11:53:22AM +0800, Lai Jiangshan wrote:
    > Paul E. McKenney wrote:
    > > Hello!
    > >
    > > This is v3 of a tracing patch for Classic RCU, which creates "rcu/rcucb"
    > > and "rcu/rcudata" files in debugfs. This patch can be handy when you
    > > need to work out why RCU is refusing to end the current grace period.
    > >
    > > Should be ready for inclusion in tip/core/rcu, Ingo, please apply.
    >
    > Hi, Paul,
    >
    > I'm sorry that I'm a little busy these days, so I have not
    > ported it to seq_file, and you lost one choice.
    >
    > I found that seq_cpumask_list() is needed when I tried to ported v2
    > to seq_file, so I introduced seq_cpumask_list() for seq_file, I'm
    > waiting procfs hackers apply that patch too.

    No problem, will be happy to see your patch whenever it is available.

    Thanx, Paul

    > Lai.
    >
    > >
    > > Changes since v2: Add flag to rcu_data to avoid printing rcu_data for
    > > CPUs that have never been online.
    > >
    > > Add documentation (below).
    > >
    > > Changes since v1: Adds (crude) tracing for rcu_data structures.
    > >
    > > Reading from the "rcu/rcucb" file results in something like the following:
    > >
    > > rcu: cur=1129 completed=1128 pending=0 s=0
    > > 0,3,7
    >
    > use "somename: 0,3,7" ? then when mask is empty, I think "somename:" is
    > better than empty line.
    >
    > > 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));
    >
    > Is strlen(rcuclassic_trace_buf) == buf - rcuclassic_trace_buf ?
    >
    > > + mutex_unlock(&rcuclassic_trace_mutex);
    > > + return bcount;
    > > +}
    > > +
    > > +static int print_one_rcu_ctrlblk(struct rcu_ctrlblk *rcp, char *buf, char *ebuf)
    > > +{
    > > + int cnt = 0;
    > > +
    > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "cur=%ld completed=%ld "
    > > + "pending=%ld s=%d\n\t",
    > > + rcp->cur, rcp->completed,
    > > + rcp->pending, rcp->signaled);
    > > + cnt += cpulist_scnprintf(&buf[cnt], ebuf - &buf[cnt], rcp->cpumask);
    > > + cnt += snprintf(&buf[cnt], ebuf - &buf[cnt], "\n");
    > > + return cnt;
    > > +}
    > > +
    > > +static ssize_t rcucb_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: ");
    > > + buf += print_one_rcu_ctrlblk(&rcu_ctrlblk, buf, ebuf);
    > > + buf += snprintf(buf, ebuf - buf, "rcu_bh: ");
    > > + buf += print_one_rcu_ctrlblk(&rcu_bh_ctrlblk, buf, ebuf);
    > > + buf += snprintf(buf, ebuf - buf, "online: ");
    > > + buf += cpulist_scnprintf(buf, ebuf - buf, cpu_online_map);
    > > + buf += snprintf(buf, ebuf - buf, "\n");
    > > + bcount = simple_read_from_buffer(buffer, count, ppos,
    > > + rcuclassic_trace_buf, strlen(rcuclassic_trace_buf));
    > > + mutex_unlock(&rcuclassic_trace_mutex);
    > > + return bcount;
    > > +}
    > > +
    > > +static struct file_operations rcudata_fops = {
    > > + .owner = THIS_MODULE,
    > > + .read = rcudata_read,
    > > +};
    > > +
    > > +static struct file_operations rcucb_fops = {
    > > + .owner = THIS_MODULE,
    > > + .read = rcucb_read,
    > > +};
    > > +
    > > +static struct dentry *rcudir, *datadir, *cbdir;
    > > +static int rcuclassic_debugfs_init(void)
    > > +{
    > > + rcudir = debugfs_create_dir("rcu", NULL);
    > > + if (!rcudir)
    > > + goto out;
    > > + datadir = debugfs_create_file("rcudata", 0444, rcudir,
    > > + NULL, &rcudata_fops);
    > > + if (!datadir)
    > > + goto free_out;
    > > + cbdir = debugfs_create_file("rcucb", 0444, rcudir, NULL, &rcucb_fops);
    > > + if (!cbdir)
    > > + goto free_out;
    > > + return 0;
    > > +free_out:
    > > + if (datadir)
    > > + debugfs_remove(datadir);
    > > + debugfs_remove(rcudir);
    > > +out:
    > > + return 1;
    > > +}
    > > +
    > > +static int __init rcuclassic_trace_init(void)
    > > +{
    > > + int ret;
    > > +
    > > + rcuclassic_trace_buf = kmalloc(RCUCLASSIC_TRACE_BUF_SIZE, GFP_KERNEL);
    > > + if (!rcuclassic_trace_buf)
    > > + return 1;
    > > + ret = rcuclassic_debugfs_init();
    > > + if (ret)
    > > + kfree(rcuclassic_trace_buf);
    > > + return ret;
    > > +}
    > > +
    > > +static void __exit rcuclassic_trace_cleanup(void)
    > > +{
    > > + debugfs_remove(datadir);
    > > + debugfs_remove(cbdir);
    > > + debugfs_remove(rcudir);
    > > + kfree(rcuclassic_trace_buf);
    > > +}
    > > +
    > > +
    > > +module_init(rcuclassic_trace_init);
    > > +module_exit(rcuclassic_trace_cleanup);
    >
    > should have:
    > MODULE_LICENSE("GPL");
    >
    > optional but recommend:
    > MODULE_AUTHOR("Paul E. McKenney");
    > MODULE_DESCRIPTION("DESCRIPTION");
    >
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > > Please read the FAQ at http://www.tux.org/lkml/
    > >
    > >
    > >
    >
    >
    >


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