Re: [PATCH v5 00/45] CPU hotplug: stop_machine()-free CPU hotplug

[Vincent Guittot <vincent.guittot@linaro.org>]

On 18 February 2013 11:51, Srivatsa S. Bhat
<srivatsa.bhat@linux.vnet.ibm.com> wrote:
> On 02/18/2013 04:04 PM, Srivatsa S. Bhat wrote:
>> On 02/18/2013 03:54 PM, Vincent Guittot wrote:
>>> On 15 February 2013 20:40, Srivatsa S. Bhat
>>> <srivatsa.bhat@linux.vnet.ibm.com> wrote:
>>>> Hi Vincent,
>>>>
>>>> On 02/15/2013 06:58 PM, Vincent Guittot wrote:
>>>>> 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!
>>>>
>>>>> 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! :-)

My tests have been done without cpuidle because i have some issues
with function tracer and cpuidle

But the cpu hotplug and cpuidle work well when I run the tests without
enabling the function tracer

Vincent

>
> 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
>