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

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

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>
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