[PATCH 0/4] /proc/schedstat and /proc/sched_debug fail at 4096

[PATCH 0/4] /proc/schedstat and /proc/sched_debug fail at 4096

[Nathan Zimmer]

When running with 4096 cores attemping to read /proc/schedstat,
/proc/sched_debug, /proc/timer_list will fail with an ENOMEM condition.
On a sufficantly large systems the total amount of data is more then 4mb, so
it won't fit into a single buffer.  The failure can also occur on smaller
systems when memory fragmentation is high.

An solution considered but not tried for sched_stat and scheddebug would to be
create an alternative mechanism to single_open but rather then calling *_show
once it calls show once per possible cpu.  If someone feels strongly that is
the way to go I can give it a spin.

Nathan Zimmer (4):
  procfs: /proc/sched_stat fails on very very large machines.
  procfs: /proc/sched_debug fails on very very large machines.
  /proc/timer_list split timer_list_show_tickdevices
  Convert timer list to be a proper seq_file.

 kernel/sched/debug.c     |   84 +++++++++++++++++++++++++++++++++-----
 kernel/sched/stats.c     |   73 ++++++++++++++++++++++++---------
 kernel/time/timer_list.c |  102 +++++++++++++++++++++++++++++++++++++---------
 3 files changed, 209 insertions(+), 50 deletions(-)

[PATCH 1/4] procfs: /proc/sched_stat fails on very very large machines.

[Nathan Zimmer]

On systems with 4096 cores doing a cat /proc/sched_stat fails.
We are trying to push all the data into a single kmalloc buffer.
The issue is on these very large machines all the data will not fit in 4mb.

A better solution is to not us the single_open mechanism but to provide
our own seq_operations.

The output should be identical to previous version and thus not need the
version number.

CC: Ingo Molnar <mingo@redhat.com> 
CC: Peter Zijlstra <peterz@infradead.org> 
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
CC: linux-kernel@vger.kernel.org
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
 kernel/sched/stats.c |   73 ++++++++++++++++++++++++++++++++++++-------------
 1 files changed, 53 insertions(+), 20 deletions(-)

diff --git a/kernel/sched/stats.c b/kernel/sched/stats.c
index 903ffa9..33a85c9 100644
--- a/kernel/sched/stats.c
+++ b/kernel/sched/stats.c
@@ -21,9 +21,13 @@ static int show_schedstat(struct seq_file *seq, void *v)
 	if (mask_str == NULL)
 		return -ENOMEM;
 
-	seq_printf(seq, "version %d\n", SCHEDSTAT_VERSION);
-	seq_printf(seq, "timestamp %lu\n", jiffies);
-	for_each_online_cpu(cpu) {
+	if (v == (void *)1) {
+		seq_printf(seq, "version %d\n", SCHEDSTAT_VERSION);
+		seq_printf(seq, "timestamp %lu\n", jiffies);
+	} else {
+
+		cpu = (unsigned long)(v - 2);
+
 		struct rq *rq = cpu_rq(cpu);
 #ifdef CONFIG_SMP
 		struct sched_domain *sd;
@@ -72,35 +76,64 @@ static int show_schedstat(struct seq_file *seq, void *v)
 		}
 		rcu_read_unlock();
 #endif
+		kfree(mask_str);
 	}
-	kfree(mask_str);
 	return 0;
 }
 
-static int schedstat_open(struct inode *inode, struct file *file)
+static void *schedstat_start(struct seq_file *file, loff_t *offset)
 {
-	unsigned int size = PAGE_SIZE * (1 + num_online_cpus() / 32);
-	char *buf = kmalloc(size, GFP_KERNEL);
-	struct seq_file *m;
-	int res;
+	unsigned long n = *offset;
 
-	if (!buf)
-		return -ENOMEM;
-	res = single_open(file, show_schedstat, NULL);
-	if (!res) {
-		m = file->private_data;
-		m->buf = buf;
-		m->size = size;
-	} else
-		kfree(buf);
-	return res;
+	if (n == 0)
+		return (void *) 1;
+
+	n--;
+
+	if (n > 0)
+		n = cpumask_next(n - 1, cpu_online_mask);
+	else
+		n = cpumask_first(cpu_online_mask);
+
+	*offset = n + 1;
+
+	if (n < nr_cpu_ids)
+		return (void *)(unsigned long)(n + 2);
+	return NULL;
+}
+
+static void *schedstat_next(struct seq_file *file, void *data, loff_t *offset)
+{
+	(*offset)++;
+	return schedstat_start(file, offset);
+}
+
+static void schedstat_stop(struct seq_file *file, void *data)
+{
+}
+
+static const struct seq_operations schedstat_sops = {
+	.start = schedstat_start,
+	.next  = schedstat_next,
+	.stop  = schedstat_stop,
+	.show  = show_schedstat,
+};
+
+static int schedstat_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &schedstat_sops);
 }
 
+static int schedstat_release(struct inode *inode, struct file *file)
+{
+	return 0;
+};
+
 static const struct file_operations proc_schedstat_operations = {
 	.open    = schedstat_open,
 	.read    = seq_read,
 	.llseek  = seq_lseek,
-	.release = single_release,
+	.release = schedstat_release,
 };
 
 static int __init proc_schedstat_init(void)
-- 
1.6.0.2

[PATCH 2/4] procfs: /proc/sched_debug fails on very very large machines.

[Nathan Zimmer]

On systems with 4096 cores attemping to read /proc/sched_debug fails.
We are trying to push all the data into a single kmalloc buffer.
The issue is on these very large machines all the data will not fit in 4mb.

A better solution is to not us the single_open mechanism but to provide
our own seq_operations and treat each cpu as an individual record.

The output should be identical to previous version.

CC: Ingo Molnar <mingo@redhat.com> 
CC: Peter Zijlstra <peterz@infradead.org> 
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
CC: linux-kernel@vger.kernel.org
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
 kernel/sched/debug.c |   84 +++++++++++++++++++++++++++++++++++++++++++------
 1 files changed, 73 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 6f79596..1ffdd42 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -253,11 +253,11 @@ static void print_cpu(struct seq_file *m, int cpu)
 	{
 		unsigned int freq = cpu_khz ? : 1;
 
-		SEQ_printf(m, "\ncpu#%d, %u.%03u MHz\n",
+		SEQ_printf(m, "cpu#%d, %u.%03u MHz\n",
 			   cpu, freq / 1000, (freq % 1000));
 	}
 #else
-	SEQ_printf(m, "\ncpu#%d\n", cpu);
+	SEQ_printf(m, "cpu#%d\n", cpu);
 #endif
 
 #define P(x)								\
@@ -314,6 +314,7 @@ do {									\
 	print_rq(m, rq, cpu);
 	rcu_read_unlock();
 	spin_unlock_irqrestore(&sched_debug_lock, flags);
+	SEQ_printf(m, "\n");
 }
 
 static const char *sched_tunable_scaling_names[] = {
@@ -322,11 +323,10 @@ static const char *sched_tunable_scaling_names[] = {
 	"linear"
 };
 
-static int sched_debug_show(struct seq_file *m, void *v)
+static void sched_debug_header(struct seq_file *m)
 {
 	u64 ktime, sched_clk, cpu_clk;
 	unsigned long flags;
-	int cpu;
 
 	local_irq_save(flags);
 	ktime = ktime_to_ns(ktime_get());
@@ -368,33 +368,95 @@ static int sched_debug_show(struct seq_file *m, void *v)
 #undef PN
 #undef P
 
-	SEQ_printf(m, "  .%-40s: %d (%s)\n", "sysctl_sched_tunable_scaling",
+	SEQ_printf(m, "  .%-40s: %d (%s)\n",
+		"sysctl_sched_tunable_scaling",
 		sysctl_sched_tunable_scaling,
 		sched_tunable_scaling_names[sysctl_sched_tunable_scaling]);
+	SEQ_printf(m, "\n");
+}
 
-	for_each_online_cpu(cpu)
-		print_cpu(m, cpu);
+static int sched_debug_show(struct seq_file *m, void *v)
+{
+	int cpu = (unsigned long)(v - 2);
 
-	SEQ_printf(m, "\n");
+	if (cpu != -1)
+		print_cpu(m, cpu);
+	else
+		sched_debug_header(m);
 
 	return 0;
 }
 
 void sysrq_sched_debug_show(void)
 {
-	sched_debug_show(NULL, NULL);
+	int cpu;
+
+	sched_debug_header(NULL);
+	for_each_online_cpu(cpu)
+		print_cpu(NULL, cpu);
+
+}
+
+static void *sched_debug_start(struct seq_file *file, loff_t *offset)
+{
+	unsigned long n = *offset;
+
+	if (n == 0)
+		return (void *) 1;
+
+	n--;
+
+	if (n > 0)
+		n = cpumask_next(n - 1, cpu_online_mask);
+	else
+		n = cpumask_first(cpu_online_mask);
+
+	*offset = n + 1;
+
+	if (n < nr_cpu_ids)
+		return (void *)(unsigned long)(n + 2);
+	return NULL;
+}
+
+static void *sched_debug_next(struct seq_file *file, void *data, loff_t *offset)
+{
+	(*offset)++;
+	return sched_debug_start(file, offset);
+}
+
+static void sched_debug_stop(struct seq_file *file, void *data)
+{
+}
+
+
+static const struct seq_operations sched_debug_sops = {
+	.start = sched_debug_start,
+	.next = sched_debug_next,
+	.stop = sched_debug_stop,
+	.show = sched_debug_show,
+};
+
+static int sched_debug_release(struct inode *inode, struct file *file)
+{
+	seq_release(inode, file);
+
+	return 0;
 }
 
 static int sched_debug_open(struct inode *inode, struct file *filp)
 {
-	return single_open(filp, sched_debug_show, NULL);
+	int ret = 0;
+
+	ret = seq_open(filp, &sched_debug_sops);
+
+	return ret;
 }
 
 static const struct file_operations sched_debug_fops = {
 	.open		= sched_debug_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= single_release,
+	.release	= sched_debug_release,
 };
 
 static int __init init_sched_debug_procfs(void)
-- 
1.6.0.2

[PATCH 3/4] /proc/timer_list split timer_list_show_tickdevices

[Nathan Zimmer]

Split timer_list_show_tickdevices out the header and just pull the rest up
to timer_list_show.  Also tweak the location of the whitespace.  This is all
to prep for the fix.

CC: John Stultz <johnstul@us.ibm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: linux-kernel@vger.kernel.org
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
 kernel/time/timer_list.c |   20 +++++++++-----------
 1 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index af5a7e9..b3dc3d6 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -133,7 +133,6 @@ static void print_cpu(struct seq_file *m, int cpu, u64 now)
 	struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
 	int i;
 
-	SEQ_printf(m, "\n");
 	SEQ_printf(m, "cpu: %d\n", cpu);
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
 		SEQ_printf(m, " clock %d:\n", i);
@@ -187,6 +186,7 @@ static void print_cpu(struct seq_file *m, int cpu, u64 now)
 
 #undef P
 #undef P_ns
+	SEQ_printf(m, "\n");
 }
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
@@ -195,7 +195,6 @@ print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
 {
 	struct clock_event_device *dev = td->evtdev;
 
-	SEQ_printf(m, "\n");
 	SEQ_printf(m, "Tick Device: mode:     %d\n", td->mode);
 	if (cpu < 0)
 		SEQ_printf(m, "Broadcast device\n");
@@ -230,12 +229,11 @@ print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
 	print_name_offset(m, dev->event_handler);
 	SEQ_printf(m, "\n");
 	SEQ_printf(m, " retries:        %lu\n", dev->retries);
+	SEQ_printf(m, "\n");
 }
 
-static void timer_list_show_tickdevices(struct seq_file *m)
+static void timer_list_show_tickdevices_header(struct seq_file *m)
 {
-	int cpu;
-
 #ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
 	print_tickdevice(m, tick_get_broadcast_device(), -1);
 	SEQ_printf(m, "tick_broadcast_mask: %08lx\n",
@@ -246,12 +244,8 @@ static void timer_list_show_tickdevices(struct seq_file *m)
 #endif
 	SEQ_printf(m, "\n");
 #endif
-	for_each_online_cpu(cpu)
-		print_tickdevice(m, tick_get_device(cpu), cpu);
 	SEQ_printf(m, "\n");
 }
-#else
-static void timer_list_show_tickdevices(struct seq_file *m) { }
 #endif
 
 static int timer_list_show(struct seq_file *m, void *v)
@@ -262,12 +256,16 @@ static int timer_list_show(struct seq_file *m, void *v)
 	SEQ_printf(m, "Timer List Version: v0.7\n");
 	SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n", HRTIMER_MAX_CLOCK_BASES);
 	SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);
+	SEQ_printf(m, "\n");
 
 	for_each_online_cpu(cpu)
 		print_cpu(m, cpu, now);
 
-	SEQ_printf(m, "\n");
-	timer_list_show_tickdevices(m);
+#ifdef CONFIG_GENERIC_CLOCKEVENTS
+	timer_list_show_tickdevices_header(m);
+	for_each_online_cpu(cpu)
+		print_tickdevice(m, tick_get_device(cpu), cpu);
+#endif
 
 	return 0;
 }
-- 
1.6.0.2

[PATCH 4/4] Convert timer list to be a proper seq_file.

[Nathan Zimmer]

Convert /proc/timer_list to a proper seq_file with its own iterator.  This is a
little more complex given that we have to make two passes with two seperate
headers.

CC: John Stultz <johnstul@us.ibm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: linux-kernel@vger.kernel.org
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
---
 kernel/time/timer_list.c |   88 +++++++++++++++++++++++++++++++++++++++------
 1 files changed, 76 insertions(+), 12 deletions(-)

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index b3dc3d6..6a2cfc2 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -253,38 +253,102 @@ static int timer_list_show(struct seq_file *m, void *v)
 	u64 now = ktime_to_ns(ktime_get());
 	int cpu;
 
-	SEQ_printf(m, "Timer List Version: v0.7\n");
-	SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n", HRTIMER_MAX_CLOCK_BASES);
-	SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);
-	SEQ_printf(m, "\n");
-
-	for_each_online_cpu(cpu)
+	if (v == (void *)1) {
+		SEQ_printf(m, "Timer List Version: v0.7\n");
+		SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n",
+			   HRTIMER_MAX_CLOCK_BASES);
+		SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);
+		SEQ_printf(m, "\n");
+	} else if (v < (void *)(nr_cpu_ids + 2)) {
+		cpu = (unsigned long)(v - 2);
 		print_cpu(m, cpu, now);
-
+	}
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
-	timer_list_show_tickdevices_header(m);
-	for_each_online_cpu(cpu)
+	else if (v == (void *)nr_cpu_ids + 2) {
+		timer_list_show_tickdevices_header(m);
+	} else {
+		cpu = (unsigned long)(v - 3 - nr_cpu_ids);
 		print_tickdevice(m, tick_get_device(cpu), cpu);
+	}
 #endif
-
 	return 0;
 }
 
+
+static void *timer_list_start(struct seq_file *file, loff_t *offset)
+{
+	unsigned long n = *offset;
+
+	if (n == 0)
+		return (void *) 1;
+
+	if (n < nr_cpu_ids + 1) {
+		n--;
+		if (n > 0)
+			n = cpumask_next(n - 1, cpu_online_mask);
+		else
+			n = cpumask_first(cpu_online_mask);
+		*offset = n + 1;
+		return (void *)(unsigned long)(n + 2);
+	}
+
+#ifdef CONFIG_GENERIC_CLOCKEVENTS
+	if (n == nr_cpu_ids + 1)
+		return (void *) (nr_cpu_ids + 2);
+
+	if (n < nr_cpu_ids * 2 + 2) {
+		n -= (nr_cpu_ids + 2);
+		if (n > 0)
+			n = cpumask_next(n - 1, cpu_online_mask);
+		else
+			n = cpumask_first(cpu_online_mask);
+		*offset = n + 2 + nr_cpu_ids;
+		return (void *)(unsigned long)(n + 3 + nr_cpu_ids);
+	}
+#endif
+
+	return NULL;
+}
+
+static void *timer_list_next(struct seq_file *file, void *data, loff_t *offset)
+{
+	(*offset)++;
+	return timer_list_start(file, offset);
+}
+
+static void timer_list_stop(struct seq_file *file, void *data)
+{
+}
+
+static const struct seq_operations timer_list_sops = {
+	.start = timer_list_start,
+	.next = timer_list_next,
+	.stop = timer_list_stop,
+	.show = timer_list_show,
+};
+
 void sysrq_timer_list_show(void)
 {
 	timer_list_show(NULL, NULL);
 }
 
+static int timer_list_release(struct inode *inode, struct file *filep)
+{
+	seq_release(inode, filep);
+
+	return 0;
+}
+
 static int timer_list_open(struct inode *inode, struct file *filp)
 {
-	return single_open(filp, timer_list_show, NULL);
+	return seq_open(filp, &timer_list_sops);
 }
 
 static const struct file_operations timer_list_fops = {
 	.open		= timer_list_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= single_release,
+	.release	= timer_list_release,
 };
 
 static int __init init_timer_list_procfs(void)
-- 
1.6.0.2