Messages in this thread | | | Date | Thu, 09 Oct 2008 14:20:22 +0800 | From | Lai Jiangshan <> | Subject | Re: [PATCH] rudimentary tracing for Classic RCU |
| |
Paul E. McKenney wrote: > Hello! > > This is a tracing patch for Classic RCU, which creates an "rcu/rcucb" > file in debugfs. This patch can be handy when you need to work out > why RCU is refusing to end the current grace period. > > Reading from the file results in something like the following: > > rcu: cur=1129 completed=1128 np=0 s=0 > 0,3,7 > rcu_bh: cur=-287 completed=-287 np=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 np= is a flag indicating that an additional RCU grace period > beyond the current one will be 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. > > Tested on x86 and Power. > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > > include/linux/rcuclassic.h | 3 + > kernel/Kconfig.preempt | 1 > kernel/Makefile | 2 > kernel/rcuclassic.c | 4 - > kernel/rcuclassic_trace.c | 126 +++++++++++++++++++++++++++++++++++++++++++++ > 5 files changed, 133 insertions(+), 3 deletions(-) > > diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h > index 4ab8436..061a272 100644 > --- a/include/linux/rcuclassic.h > +++ b/include/linux/rcuclassic.h > @@ -54,6 +54,9 @@ 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) > { > 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
I think that we can move it to lib/Kconfig.debug.
> 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 aad93cd..517eaa9 100644 > --- a/kernel/rcuclassic.c > +++ b/kernel/rcuclassic.c > @@ -57,13 +57,13 @@ 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, > .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, > .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock), > diff --git a/kernel/rcuclassic_trace.c b/kernel/rcuclassic_trace.c > new file mode 100644 > index 0000000..f8b9313 > --- /dev/null > +++ b/kernel/rcuclassic_trace.c > @@ -0,0 +1,126 @@ > +/* > + * 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 (20*NR_CPUS + 100) > + > +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 " > + "np=%d s=%d\n\t", > + rcp->cur, rcp->completed, > + rcp->next_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 rcucb_fops = { > + .owner = THIS_MODULE, > + .read = rcucb_read, > +}; > + > +static struct dentry *rcudir, *cbdir; > +static int rcuclassic_debugfs_init(void)
add __init: static int __init rcuclassic_debugfs_init(void)
> +{ > + rcudir = debugfs_create_dir("rcu", NULL); > + if (!rcudir) > + goto out; > + cbdir = debugfs_create_file("rcucb", 0444, rcudir, NULL, &rcucb_fops); > + if (!cbdir) > + goto free_out; > + return 0; > +free_out: > + 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);
I'm wondering about this. rcuclassic_trace_buf is kmalloc-ed when init module.
In this case, why not define it as: static char buf[20*NR_CPUS + 100];
and use it like: pos += snprintf(buf + cnt, sizeof(buf) - cnt, ...);
> + 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(cbdir); > + debugfs_remove(rcudir); > + kfree(rcuclassic_trace_buf); > +} > + > + > +module_init(rcuclassic_trace_init); > +module_exit(rcuclassic_trace_cleanup);
I think this trace file shows too little vars for classic rcu.
It is better that this trace file shows more data. such as some data in struct rcu_data(quiescent state handling fields, batch, qlen).
or add new files: rcu/rcu_data<cpu#>
Thanks, Lai
| |