From mboxrd@z Thu Jan  1 00:00:00 1970
From: Arjan van de Ven <arjan@linux.intel.com>
Subject: Re: [PATCH] PERF(kernel): Cleanup power events V2
Date: Tue, 26 Oct 2010 13:52:00 -0700
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To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Pierre Tardy <tardyp@gmail.com>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>, Thomas Renninger <trenn@suse.de>, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Frank Eigler <fche@redhat.com>, Steven Rostedt <rostedt@goodmis.org>, Kevin Hilman <khilman@deeprootsystems.com>, linux-omap@vger.kernel.org, linux-pm@lists.linux-foundation.org, linux-trace-users@vger.kernel.org, Jean Pihet <jean.pihet@newoldbits.com>, Frederic Weisbecker <fweisbec@gmail.com>, Tejun Heo <tj@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

On 10/26/2010 1:38 PM, Rafael J. Wysocki wrote:
> On Tuesday, October 26, 2010, Pierre Tardy wrote:
>> On Tue, Oct 26, 2010 at 2:08 PM, Rafael J. Wysocki<rjw@sisk.pl>  wrote:
>>> On Tuesday, October 26, 2010, Pierre Tardy wrote:
>>>> On Tue, Oct 26, 2010 at 12:58 PM, Peter Zijlstra<peterz@infradead.org>  wrote:
>>>>> On Tue, 2010-10-26 at 11:56 -0500, Pierre Tardy wrote:
>>>>>> +       trace_runtime_pm_usage(dev, atomic_read(&dev->power.usage_count)+1);
>>>>>>          atomic_inc(&dev->power.usage_count);
>>>>> That's terribly racy..
>>>>>
>>>> I know. I'm not proud of this.. As I said, this is preliminary patch.
>>>> We dont really need to have this prev_usage. This is just for debug.
>>>> It mayprobably endup with something like:
>>>>
>>>>           atomic_inc(&dev->power.usage_count);
>>>> +       trace_power_device_usage(dev);
>>> Well, please tell me what you're trying to achieve.
>> Please see attached the kind of pytimechart output I'm trying to
>> achieve (yes, this chart is not coherent, seems I'm still missing some
>> traces)
>>
>> We basically want to have a trace point eachtime the usage_counter
>> changes, so that I can display nice timecharts, and Arjan can have the
>> comm of the process that eventually generated the rpm_get, in order to
>> pinpoint it in powertop.
>>
>> What you dont see in the above two lines is that
>> trace_power_device_usage(dev); actually reads the usage_count, as well
>> as the driver and device name.
> I'm afraid that for this to really work you'd need to put usage_count under a
> spinlock along with your trace point, which I'm not really sure I like.
>
> Besides, I'm not really sure the manipulations of usage_count are worth
> tracing.

what's most interesting is the 0->1  and 1->0 transitions.