linux-kernel - Re: [PATCH v7 6/6] cpufreq: powernv: Add sysfs attributes to show throttle stats

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Message-ID: <56A9E136.8090900@linux.vnet.ibm.com>
Date:	Thu, 28 Jan 2016 15:06:54 +0530
From:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	rjw@...ysocki.net, linux-pm@...r.kernel.org, pc@...ibm.com,
	anton@...ba.org, ego@...ux.vnet.ibm.com,
	shreyas@...ux.vnet.ibm.com, bsingharora@...il.com,
	mpe@...erman.id.au, linux-api@...r.kernel.org
Subject: Re: [PATCH v7 6/6] cpufreq: powernv: Add sysfs attributes to show
 throttle stats

Hi Viresh,

On 01/28/2016 02:10 PM, Viresh Kumar wrote:
> On 28-01-16, 12:55, Shilpasri G Bhat wrote:
>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> index b683e8e..dea4620 100644
>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>> @@ -271,3 +271,48 @@ Description:	Parameters for the CPU cache attributes
>>  			- WriteBack: data is written only to the cache line and
>>  				     the modified cache line is written to main
>>  				     memory only when it is replaced
>> +
>> +What:		/sys/devices/system/cpu/cpufreq/chip*/throttle_stats
> 
> What about the chip directory ? Shouldn't that be documented? And
> shouldn't that mention that this is just for powerpc ?
> 
> And before that, I don't think that you are doing this properly. I am
> sorry that I never came to a point where I could review it, and you
> continued with it, version after version.
> 
> But, I really have strong objections to the way this is done. And you
> are making things more complex then they are.
> 
> So, these stats are per-policy, right ?

First of all sorry about the version log.
No these stats are not per-policy. They are per-chip. The throttle event is
common for all cores in the chip.

> 
> Then why aren't they added on the policy->kobj instead, just like
> cpufreq-stats? And maybe inside cpufreq-stats folder only?
> 
> That will solve many complexities you have in place here and will look
> sane as well.
> 
> Right now, you have stats as two places, cpu/cpufreq/chip/ and
> cpu/cpuX/cpufreq/stats/, which doesn't look wise and adds to
> confusion.
> 
> What do you say?
> 

Yes agree that it will be much cleaner with policy->kobj. But using policy->kobj
will result in multiple copies of the throttle-chip stats exported for each
policy in the chip. And moving it to cpu/cpuX/cpufreq/stats/
will add a dependency on CONFIG_CPU_FREQ_STAT

We want throttle attributes to be either in cpu/cpufreq or cpu/cpuX/cpufreq. If
multiple copies is not an issue, then I will move it to cpu/cpuX/cpufreq.

Thanks and Regards,
Shilpa