linux-kernel - Re: [PATCH v2] power: new trace event to print device suspend and resume time

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Date:	Wed, 17 Jul 2013 16:30:38 +0000
From:	Shuah Khan <shuah.kh@...sung.com>
To:	Joe Perches <joe@...ches.com>, "rjw@...k.pl" <rjw@...k.pl>
Cc:	"len.brown@...el.com" <len.brown@...el.com>,
	"pavel@....cz" <pavel@....cz>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"shuahkhan@...il.com" <shuahkhan@...il.com>,
	Shuah Khan <shuah.kh@...sung.com>
Subject: Re: [PATCH v2] power: new trace event to print device suspend and
 resume time

On 07/17/2013 10:09 AM, Joe Perches wrote:
> On Wed, 2013-07-17 at 09:57 -0600, Shuah Khan wrote:
>> A new trace event is added to pm events to print time it takes to suspend and
>> resume a device. It generates trace message that includes device, driver,
>> parent information in addition to the type of pm ops invoked as well as the
>> pm event and error status from the pm ops. Example trace below:
>>
>> bash-2484  [001] ....   907.330148: device_pm_report_time: backlight acpi_video0 parent=0000:00:02.0 state=freeze ops=class  usecs=0 err=0
>>
>> bash-2484  [001] ....   909.906743: device_pm_report_time: backlight acpi_video0 parent=0000:00:02.0 state=restore ops=class  usecs=0 err=0
>

Hi Joe,

> Hi again Shuah.
>
> A few things:
>
>> diff --git a/include/trace/events/power.h b/include/trace/events/power.h
> []
>> +	TP_printk("%s %s parent=%s state=%s ops=%s usecs=%lld err=%d\n",
>
> As I wrote before, do not end a TP_printk with "\n",
>
> All TP_printks are self-contained and are not possible
> to use a thing like pr_cont so no newline is ever used.
>
> Use:
>
> 	TP_printk("%s %s parent=%s state=%s ops=%s usecs=%lld err=%d",

Sorry. Missed that one. Not intentional, just an oversight. :) I should 
fix that one.

>
> Given the data is in nsecs, why use usecs for the time?
> I think full resolution would be better.

My intent to was to match the time units to the original pm_print_times.

Rafael! Do you have any preference as to usecs vs. nsecs?

>
> Why are there two spaces after "ops=class"? One would be more normal.
>
>

This one is tough. The ops string that gets generated in conditionals in 
__device_suspend() and device_resume() routines, has an extra space at 
the end. I am not sure why that was done and the subsequent pr_* that 
print that string also depend on that extra space at the end. I don't 
have an easy way to fix it without changing lots of code where this 
string is generated. Hence, I chose to leave the extra space in. I also 
didn't want to propagate that assumption that there is an extra space 
into this new tracepoint.

I could truncate the string before I pass it to the new tracepoint 
routine, however I don't like that idea. One thing I can do is, generate 
separate patch that fixes the extra space issue. That would address the 
extra space in all cases.

-- Shuah

Shuah Khan, Linux Kernel Developer - Open Source Group Samsung Research 
America (Silicon Valley) shuah.kh@...sung.com | (970) 672-0658
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