Re: [PATCH] v3 rudimentary tracing for Classic RCU

From: Paul E. McKenney
Date: Tue Oct 14 2008 - 11:14:51 EST

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In reply to: Lai Jiangshan: "Re: [PATCH] v3 rudimentary tracing for Classic RCU"
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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@xxxxxxxxxxxxxxxxxx>
> > ---
> >
> > 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");
>
> > --
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> > Please read the FAQ at http://www.tux.org/lkml/
> >
> >
> >
>
>
>
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Next message: Christoph Hellwig: "Re: [PATCH] block: add BIG FAT WARNING toCONFIG_DEBUG_BLOCK_EXT_DEVT"
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