linux-kernel - Re: [PATCH] power, trace: add tracing for device

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Date:	Fri, 18 May 2012 11:57:58 -0700
From:	Sameer Nanda <snanda@...omium.org>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	rob@...dley.net, len.brown@...el.com, pavel@....cz, rjw@...k.pl,
	rostedt@...dmis.org, fweisbec@...il.com, mingo@...hat.com,
	jkosina@...e.cz, standby24x7@...il.com, jj@...osbits.net,
	paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH] power, trace: add tracing for device_resume

On Fri, May 18, 2012 at 11:37 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, May 18, 2012 at 11:27:23AM -0700, Sameer Nanda wrote:
>> Added event tracing for device_resume. This helps quickly pinpoint which
>> devices take a long time to resume.
>>
>> Signed-off-by: Sameer Nanda <snanda@...omium.org>
>> ---
>>  Documentation/trace/events-power.txt |   20 +++++++++++
>>  drivers/base/power/main.c            |   10 ++++++
>>  include/trace/events/power.h         |   59 ++++++++++++++++++++++++++++++++++
>>  3 files changed, 89 insertions(+), 0 deletions(-)
>>
>> diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.txt
>> index cf794af..dbfb7f0 100644
>> --- a/Documentation/trace/events-power.txt
>> +++ b/Documentation/trace/events-power.txt
>> @@ -88,3 +88,23 @@ power_domain_target        "%s state=%lu cpu_id=%lu"
>>  The first parameter gives the power domain name (e.g. "mpu_pwrdm").
>>  The second parameter is the power domain target state.
>>
>> +4. Device resume events
>> +=======================
>> +The device resume events are used for measuring the time taken to resume
>> +devices.
>> +
>> +device_resume_in     "device=%s driver=%s"
>> +device_resume_waited "device=%s driver=%s time_delta=%lld"
>> +device_resume_out    "device=%s driver=%s time_delta=%lld"
>> +
>> +The first parameter is the device that is being resumed.
>> +
>> +The second parameter is the driver associated with the device being resumed.
>> +
>> +The third parameter in device_resume_waited is the time delta from the entry
>> +point of device_resume to the wait completion of parent device being resumed.
>> +The unit for time_delta is us.
>> +
>> +The third parameter in device_resume_out is the time delta from the wait
>> +completion of parent device being resumed to device_resume being completed.
>> +The unit for time_delta is us.
>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>> index b462c0e..3ed01cd 100644
>> --- a/drivers/base/power/main.c
>> +++ b/drivers/base/power/main.c
>> @@ -28,6 +28,7 @@
>>  #include <linux/sched.h>
>>  #include <linux/async.h>
>>  #include <linux/suspend.h>
>> +#include <trace/events/power.h>
>>
>>  #include "../base.h"
>>  #include "power.h"
>> @@ -565,11 +566,19 @@ static int device_resume(struct device *dev, pm_message_t state, bool async)
>>       char *info = NULL;
>>       int error = 0;
>>       bool put = false;
>> +     s64 in_time = ktime_to_us(ktime_get());
>> +     s64 wait_done_time;
>> +
>> +     trace_device_resume_in(dev);
>>
>>       TRACE_DEVICE(dev);
>>       TRACE_RESUME(0);
>
> Don't these TRACE_DEVICE() and TRACE_RESUME() calls already provide you
> the same information you are wanting to determine above if you look at
> the timestamps of the events?

AFAICT, they are used for something completely different -- help solve
suspend/resume issues by saving a hash in the RTC of the last device
that suspended/resumed.  They don't use the perf tracing mechanism at
all.

>  Can you not do time processing in
> userspace?

Did you mean by using the TRACE_DEVICE/TRACE_RESUME functionality or
something else?

>
> confused,
>
> greg k-h



-- 
Sameer
--
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