Preempt-RCU: implementation
This patch implements a new version of RCU which allows its read-side
critical sections to be preempted. It uses a set of counter pairs
to keep track of the read-side critical sections and flips them
when all tasks exit read-side critical section. The details
of this implementation can be found in this paper -
http://www.rdrop.com/users/paulmck/RCU/OLSrtRCU.2006.08.11a.pdf
and the article-
http://lwn.net/Articles/253651/
This patch was developed as a part of the -rt kernel development and
meant to provide better latencies when read-side critical sections of
RCU don't disable preemption. As a consequence of keeping track of RCU
readers, the readers have a slight overhead (optimizations in the paper).
This implementation co-exists with the "classic" RCU implementations
and can be switched to at compiler.
Also includes RCU tracing summarized in debugfs.
[ akpm@linux-foundation.org: build fixes on non-preempt architectures ]
Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@us.ibm.com>
Reviewed-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/rcupreempt_trace.c b/kernel/rcupreempt_trace.c
new file mode 100644
index 0000000..49ac4947
--- /dev/null
+++ b/kernel/rcupreempt_trace.c
@@ -0,0 +1,330 @@
+/*
+ * Read-Copy Update tracing for realtime 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, 2006
+ *
+ * Papers: http://www.rdrop.com/users/paulmck/RCU
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU/ *.txt
+ *
+ */
+#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/rcupdate.h>
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+#include <linux/rcupreempt_trace.h>
+#include <linux/debugfs.h>
+
+static struct mutex rcupreempt_trace_mutex;
+static char *rcupreempt_trace_buf;
+#define RCUPREEMPT_TRACE_BUF_SIZE 4096
+
+void rcupreempt_trace_move2done(struct rcupreempt_trace *trace)
+{
+ trace->done_length += trace->wait_length;
+ trace->done_add += trace->wait_length;
+ trace->wait_length = 0;
+}
+void rcupreempt_trace_move2wait(struct rcupreempt_trace *trace)
+{
+ trace->wait_length += trace->next_length;
+ trace->wait_add += trace->next_length;
+ trace->next_length = 0;
+}
+void rcupreempt_trace_try_flip_1(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->rcu_try_flip_1);
+}
+void rcupreempt_trace_try_flip_e1(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->rcu_try_flip_e1);
+}
+void rcupreempt_trace_try_flip_i1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_i1++;
+}
+void rcupreempt_trace_try_flip_ie1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ie1++;
+}
+void rcupreempt_trace_try_flip_g1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_g1++;
+}
+void rcupreempt_trace_try_flip_a1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_a1++;
+}
+void rcupreempt_trace_try_flip_ae1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ae1++;
+}
+void rcupreempt_trace_try_flip_a2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_a2++;
+}
+void rcupreempt_trace_try_flip_z1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_z1++;
+}
+void rcupreempt_trace_try_flip_ze1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_ze1++;
+}
+void rcupreempt_trace_try_flip_z2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_z2++;
+}
+void rcupreempt_trace_try_flip_m1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_m1++;
+}
+void rcupreempt_trace_try_flip_me1(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_me1++;
+}
+void rcupreempt_trace_try_flip_m2(struct rcupreempt_trace *trace)
+{
+ trace->rcu_try_flip_m2++;
+}
+void rcupreempt_trace_check_callbacks(struct rcupreempt_trace *trace)
+{
+ trace->rcu_check_callbacks++;
+}
+void rcupreempt_trace_done_remove(struct rcupreempt_trace *trace)
+{
+ trace->done_remove += trace->done_length;
+ trace->done_length = 0;
+}
+void rcupreempt_trace_invoke(struct rcupreempt_trace *trace)
+{
+ atomic_inc(&trace->done_invoked);
+}
+void rcupreempt_trace_next_add(struct rcupreempt_trace *trace)
+{
+ trace->next_add++;
+ trace->next_length++;
+}
+
+static void rcupreempt_trace_sum(struct rcupreempt_trace *sp)
+{
+ struct rcupreempt_trace *cp;
+ int cpu;
+
+ memset(sp, 0, sizeof(*sp));
+ for_each_possible_cpu(cpu) {
+ cp = rcupreempt_trace_cpu(cpu);
+ sp->next_length += cp->next_length;
+ sp->next_add += cp->next_add;
+ sp->wait_length += cp->wait_length;
+ sp->wait_add += cp->wait_add;
+ sp->done_length += cp->done_length;
+ sp->done_add += cp->done_add;
+ sp->done_remove += cp->done_remove;
+ atomic_set(&sp->done_invoked, atomic_read(&cp->done_invoked));
+ sp->rcu_check_callbacks += cp->rcu_check_callbacks;
+ atomic_set(&sp->rcu_try_flip_1,
+ atomic_read(&cp->rcu_try_flip_1));
+ atomic_set(&sp->rcu_try_flip_e1,
+ atomic_read(&cp->rcu_try_flip_e1));
+ sp->rcu_try_flip_i1 += cp->rcu_try_flip_i1;
+ sp->rcu_try_flip_ie1 += cp->rcu_try_flip_ie1;
+ sp->rcu_try_flip_g1 += cp->rcu_try_flip_g1;
+ sp->rcu_try_flip_a1 += cp->rcu_try_flip_a1;
+ sp->rcu_try_flip_ae1 += cp->rcu_try_flip_ae1;
+ sp->rcu_try_flip_a2 += cp->rcu_try_flip_a2;
+ sp->rcu_try_flip_z1 += cp->rcu_try_flip_z1;
+ sp->rcu_try_flip_ze1 += cp->rcu_try_flip_ze1;
+ sp->rcu_try_flip_z2 += cp->rcu_try_flip_z2;
+ sp->rcu_try_flip_m1 += cp->rcu_try_flip_m1;
+ sp->rcu_try_flip_me1 += cp->rcu_try_flip_me1;
+ sp->rcu_try_flip_m2 += cp->rcu_try_flip_m2;
+ }
+}
+
+static ssize_t rcustats_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ struct rcupreempt_trace trace;
+ ssize_t bcount;
+ int cnt = 0;
+
+ rcupreempt_trace_sum(&trace);
+ mutex_lock(&rcupreempt_trace_mutex);
+ snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "ggp=%ld rcc=%ld\n",
+ rcu_batches_completed(),
+ trace.rcu_check_callbacks);
+ snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "na=%ld nl=%ld wa=%ld wl=%ld da=%ld dl=%ld dr=%ld di=%d\n"
+ "1=%d e1=%d i1=%ld ie1=%ld g1=%ld a1=%ld ae1=%ld a2=%ld\n"
+ "z1=%ld ze1=%ld z2=%ld m1=%ld me1=%ld m2=%ld\n",
+
+ trace.next_add, trace.next_length,
+ trace.wait_add, trace.wait_length,
+ trace.done_add, trace.done_length,
+ trace.done_remove, atomic_read(&trace.done_invoked),
+ atomic_read(&trace.rcu_try_flip_1),
+ atomic_read(&trace.rcu_try_flip_e1),
+ trace.rcu_try_flip_i1, trace.rcu_try_flip_ie1,
+ trace.rcu_try_flip_g1,
+ trace.rcu_try_flip_a1, trace.rcu_try_flip_ae1,
+ trace.rcu_try_flip_a2,
+ trace.rcu_try_flip_z1, trace.rcu_try_flip_ze1,
+ trace.rcu_try_flip_z2,
+ trace.rcu_try_flip_m1, trace.rcu_try_flip_me1,
+ trace.rcu_try_flip_m2);
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static ssize_t rcugp_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ long oldgp = rcu_batches_completed();
+ ssize_t bcount;
+
+ mutex_lock(&rcupreempt_trace_mutex);
+ synchronize_rcu();
+ snprintf(rcupreempt_trace_buf, RCUPREEMPT_TRACE_BUF_SIZE,
+ "oldggp=%ld newggp=%ld\n", oldgp, rcu_batches_completed());
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static ssize_t rcuctrs_read(struct file *filp, char __user *buffer,
+ size_t count, loff_t *ppos)
+{
+ int cnt = 0;
+ int cpu;
+ int f = rcu_batches_completed() & 0x1;
+ ssize_t bcount;
+
+ mutex_lock(&rcupreempt_trace_mutex);
+
+ cnt += snprintf(&rcupreempt_trace_buf[cnt], RCUPREEMPT_TRACE_BUF_SIZE,
+ "CPU last cur F M\n");
+ for_each_online_cpu(cpu) {
+ long *flipctr = rcupreempt_flipctr(cpu);
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "%3d %4ld %3ld %d %d\n",
+ cpu,
+ flipctr[!f],
+ flipctr[f],
+ rcupreempt_flip_flag(cpu),
+ rcupreempt_mb_flag(cpu));
+ }
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "ggp = %ld, state = %s\n",
+ rcu_batches_completed(),
+ rcupreempt_try_flip_state_name());
+ cnt += snprintf(&rcupreempt_trace_buf[cnt],
+ RCUPREEMPT_TRACE_BUF_SIZE - cnt,
+ "\n");
+ bcount = simple_read_from_buffer(buffer, count, ppos,
+ rcupreempt_trace_buf, strlen(rcupreempt_trace_buf));
+ mutex_unlock(&rcupreempt_trace_mutex);
+ return bcount;
+}
+
+static struct file_operations rcustats_fops = {
+ .owner = THIS_MODULE,
+ .read = rcustats_read,
+};
+
+static struct file_operations rcugp_fops = {
+ .owner = THIS_MODULE,
+ .read = rcugp_read,
+};
+
+static struct file_operations rcuctrs_fops = {
+ .owner = THIS_MODULE,
+ .read = rcuctrs_read,
+};
+
+static struct dentry *rcudir, *statdir, *ctrsdir, *gpdir;
+static int rcupreempt_debugfs_init(void)
+{
+ rcudir = debugfs_create_dir("rcu", NULL);
+ if (!rcudir)
+ goto out;
+ statdir = debugfs_create_file("rcustats", 0444, rcudir,
+ NULL, &rcustats_fops);
+ if (!statdir)
+ goto free_out;
+
+ gpdir = debugfs_create_file("rcugp", 0444, rcudir, NULL, &rcugp_fops);
+ if (!gpdir)
+ goto free_out;
+
+ ctrsdir = debugfs_create_file("rcuctrs", 0444, rcudir,
+ NULL, &rcuctrs_fops);
+ if (!ctrsdir)
+ goto free_out;
+ return 0;
+free_out:
+ if (statdir)
+ debugfs_remove(statdir);
+ if (gpdir)
+ debugfs_remove(gpdir);
+ debugfs_remove(rcudir);
+out:
+ return 1;
+}
+
+static int __init rcupreempt_trace_init(void)
+{
+ mutex_init(&rcupreempt_trace_mutex);
+ rcupreempt_trace_buf = kmalloc(RCUPREEMPT_TRACE_BUF_SIZE, GFP_KERNEL);
+ if (!rcupreempt_trace_buf)
+ return 1;
+ return rcupreempt_debugfs_init();
+}
+
+static void __exit rcupreempt_trace_cleanup(void)
+{
+ debugfs_remove(statdir);
+ debugfs_remove(gpdir);
+ debugfs_remove(ctrsdir);
+ debugfs_remove(rcudir);
+ kfree(rcupreempt_trace_buf);
+}
+
+
+module_init(rcupreempt_trace_init);
+module_exit(rcupreempt_trace_cleanup);