On 02/18/2013 04:04 PM, Srivatsa S. Bhat wrote:

On 02/18/2013 03:54 PM, Vincent Guittot wrote:

quoted

On 15 February 2013 20:40, Srivatsa S. Bhat
[off-list ref] wrote:

quoted

Hi Vincent,

On 02/15/2013 06:58 PM, Vincent Guittot wrote:

quoted

Hi Srivatsa,

I have run some tests with you branch (thanks Paul for the git tree)
and you will find results below.

Thank you very much for testing this patchset!

quoted

The tests condition are:
- 5 CPUs system in 2 clusters
- The test plugs/unplugs CPU2 and it increases the system load each 20
plug/unplug sequence with either more cyclictests threads
- The test is done with all CPUs online and with only CPU0 and CPU2

The main conclusion is that there is no differences with and without
your patches with my stress tests. I'm not sure that it was the
expected results but the cpu_down is already quite low : 4-5ms in
average

Atleast my patchset doesn't perform _worse_ than mainline, with respect
to cpu_down duration :-)

yes exactly and it has pass  more than 400 consecutive plug/unplug on
an ARM platform

Great! However, did you turn on CPU_IDLE during your tests?

In my tests, I had turned off cpu idle in the .config, like I had mentioned in
the cover letter. I'm struggling to get it working with CPU_IDLE/INTEL_IDLE
turned on, because it gets into a lockup almost immediately. It appears that
the lock-holder of clockevents_lock never releases it, for some reason..
See below for the full log. Lockdep has not been useful in debugging this,
unfortunately :-(

Ah, nevermind, the following diff fixes it :-) I had applied this fix on v5
and tested but it still had races where I used to hit the lockups. Now after
I fixed all the memory barrier issues that Paul and Oleg pointed out in v5,
I applied this fix again and tested it just now - it works beautifully! :-)

I'll include this fix and post a v6 soon.

Regards,
Srivatsa S. Bhat

--------------------------------------------------------------------------->

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 30b6de0..ca340fd 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/notifier.h>
 #include <linux/smp.h>
+#include <linux/cpu.h>
 
 #include "tick-internal.h"
 

@@ -431,6 +432,7 @@ void clockevents_notify(unsigned long reason, void *arg)
 	unsigned long flags;
 	int cpu;
 
+	get_online_cpus_atomic();
 	raw_spin_lock_irqsave(&clockevents_lock, flags);
 	clockevents_do_notify(reason, arg);
 

@@ -459,6 +461,7 @@ void clockevents_notify(unsigned long reason, void *arg)
 		break;
 	}
 	raw_spin_unlock_irqrestore(&clockevents_lock, flags);
+	put_online_cpus_atomic();
 }
 EXPORT_SYMBOL_GPL(clockevents_notify);
 #endif