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

Nathan Zimmer
2013-01-15T21:46:19Z

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>)
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