Messages in this thread | | | Date | Tue, 14 Oct 2008 07:35:20 -0700 | From | "Paul E. McKenney" <> | Subject | 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@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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