Re: [PATCH v2] timer stats: add a 'status' line to timer usage statistics

[Dong Zhu <bluezhudong@gmail.com>]

Hi Ingo and John,

On Thu, Oct 10, 2013 at 06:35:19AM +0200, Ingo Molnar wrote:
> 
> * Dong Zhu <bluezhudong@gmail.com> wrote:
> 
> > From f41628c61d8a9172677ba33a55b61e37ce28f7a6 Mon Sep 17 00:00:00 2001
> > From: Dong Zhu <bluezhudong@gmail.com> 
> > Date: Thu, 10 Oct 2013 10:38:13 +0800
> > 
> > When we stop timer statistics collection (via echo 0 > 
> > /proc/timers_stats), the statistics data is still exported as if it were 
> > correct, which can cause applicaitons to misuse the statistics.
> 
> What misuse do you mean?
> 
> > This patch resets the statistics when we stop collecting them, to avoid 
> > this problem.
> 
> Well, this loses the handy 'snapshot' property of /proc/timer_stats. 
> Before this change one could do:
> 
> 	echo 1 > /proc/timers_stats
> 	sleep 60 # run system workload
> 	echo 0 > /proc/timers_stats
> 
> and examine the 1-minute collection result without it changing. Your 
> change, if I understand it correctly, zeroes it all out.

Yes, I am wrong about it. Thanks for pointing this out and pretty sorry
for confusing you John.

> 
> Instead of this change I'd suggest adding a 'status' line, with two 
> outputs:
> 
> 	Status: collection active
> 
> 	Status: collection disabled
> 

Agree, I modified this patch and resubmited it again, Could you help
reviewing it again ? Thanks !

>From 263c40abea8011c82582b2d671ae783b26f44bd5 Mon Sep 17 00:00:00 2001
From: Dong Zhu <bluezhudong@gmail.com> 
Date: Thu, 10 Oct 2013 13:46:08 +0800

We can enable|disable timer statistics collection (via echo [1|0] >
/proc/timers_stats), this patch adds a 'status' line to display the
current timer collection status.

Signed-off-by: Dong Zhu <bluezhudong@gmail.com>
---
 kernel/time/timer_stats.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/time/timer_stats.c b/kernel/time/timer_stats.c
index 0b537f2..bac5e91 100644
--- a/kernel/time/timer_stats.c
+++ b/kernel/time/timer_stats.c
@@ -303,6 +303,10 @@ static int tstats_show(struct seq_file *m, void *v)
 	if (atomic_read(&overflow_count))
 		seq_printf(m, "Overflow: %d entries\n",
 			atomic_read(&overflow_count));
+	if (timer_stats_active)
+		seq_puts(m, "Status: collection active\n");
+	else
+		seq_puts(m, "Status: collection disabled\n");
 
 	for (i = 0; i < nr_entries; i++) {
 		entry = entries + i;
-- 
1.7.11.7


-- 
Best Regards,
Dong Zhu